RN Expert Guides: Cardiovascular Care, 1st Edition (2008)

Chapter 3. Diagnostic Tests and Procedures

Advances in diagnostic testing allow for earlier and easier diagnosis and treatment of cardiovascular disorders. For example, in some patients, echocardiography, a noninvasive and risk-free test, can provide as much diagnostic information about valvular heart disease as cardiac catheterization, an invasive and high-risk test. Monitoring and testing also help guide and evaluate treatment and identify complications. Before the patient undergoes testing, explain the procedure in terms he can easily understand. Make sure an informed consent form is signed, if necessary. Because these diagnostic tests may cause anxiety, be sure to provide emotional support.

Cardiac tests range from a relatively simple test that analyzes the patient's blood for cardiac enzymes, proteins, and clotting time to very sophisticated imaging and radiographic tests that reveal a detailed image of the heart. Other cardiovascular tests include various forms of electrocardiography, ultrasound, and hemodynamic monitoring.

CARDIAC ENZYMES AND PROTEINS

Analyzing cardiac enzymes and proteins (markers) is an important step in diagnosing acute myocardial infarction (MI) and in evaluating other cardiac disorders. After an MI, damaged cardiac tissue releases significant amounts of enzymes and proteins into the blood. Specific blood tests help reveal the extent of cardiac damage and help monitor healing progress.

Creatine kinase and isoforms

Creatine kinase (CK) is present in heart muscle, skeletal muscle, and brain tissue. Its isoenzymes, CK-MB, is found specifically in the heart muscle. Elevated levels of CK-MB reliably indicate acute MI. Generally, CK-MB levels rise 4 to 8 hours after the onset of an acute MI, peak after 20 hours, and may remain elevated for up to 72 hours. (See Cardiac enzyme and protein patterns.) Normal CK levels are 55 to 170 units/L for men and 30 to 135 units/L for women. CK-MB levels are normally less than 5% for men and women.

NURSING CONSIDERATIONS

·

Explain to the patient that the test will help confirm or rule out MI.

·

Inform the patient that blood samples will be drawn at timed intervals.

·

Muscle trauma caused by I.M. injections, cardioversion, or cardiopulmonary resuscitation can raise CK levels.

·

Patients who are muscular may have significantly higher CK levels.

·

Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately after collection.

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

Myoglobin

Myoglobin, which is normally found in skeletal and cardiac muscle, functions as an oxygen-bonding muscle protein. It's released into the bloodstream when ischemia, trauma, and inflammation of the muscle occur. Normal myoglobin values are 0 to 0.09 mcg/ml.

Rising myoglobin levels are one of the first markers of cardiac injury after an acute MI. Levels may rise within 2 hours, peak within 4 hours, and return to baseline by 24 hours. However, because skeletal muscle damage may also cause myoglobin levels to rise, other tests (such as CK-MB or troponin) may be required to determine myocardial injury.

·

I.M. injections, recent angina, or cardioversion can cause elevated myoglobin levels.

·

Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately after collection.

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

Troponin I and troponin T

Troponin is a protein found in skeletal and cardiac muscles. Two isotypes of troponin, troponin I and troponin T, are found in the myocardium. When injury occurs to the myocardial tissue, these proteins are released into the bloodstream. Troponin T can also be found in skeletal muscle. Troponin I, however, is found only in the myocardium. In fact, it's more specific to myocardial damage than CK, CK-MB isoenzymes, and myoglobin. Because troponin T levels can occur in certain muscle disorders or renal failure, they're less specific for myocardial injury than troponin I levels.

CARDIAC ENZYME AND PROTEIN PATTERNS

Because they're released by damaged tissue, serum proteins and isoenzymes (catalytic proteins that vary in concentration in specific organs) can help identify the compromised organ and assess the extent of damage. After acute myocardial infarction, cardiac enzymes and proteins rise and fall in a characteristic pattern, as shown in this graph.

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Normal troponin I levels are less than 0.35 mcg/L and normal troponin T levels are less than 0.1 mcg/L. Troponin I levels greater than 2 mcg/L suggest cardiac injury.

Troponin levels rise within 3 to 6 hours after myocardial damage. Troponin I peaks in 14 to 20 hours, with a return to baseline in 5 to 7 days, and troponin T peaks in 12 to 24 hours, with a return to baseline in 10 to 15 days. Because troponin levels stay elevated for a prolonged time, they can detect an infarction that occurred several days earlier. Troponin T levels can be determined at the bedside in minutes, making them a useful tool for determining treatment in acute MI.

NURSING CONSIDERATIONS

·

Inform the patient that he need not restrict food or fluids before the test.

·

Tell the patient that multiple blood samples may be drawn.

·

Sustained vigorous exercise, cardiotoxic drugs such as doxorubicin, renal disease, and certain surgical procedures can cause elevated troponin T levels.

·

Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately after collection.

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

Ischemia modified albumin

The ischemia modified albumin (IMA) test measures the changes in human serum albumin when it comes in contact with ischemic tissue. When ischemia occurs, IMA will rise rapidly. In over 80% of patients with acute coronary syndrome, IMA has been found to be elevated. However, IMA doesn't rise in tissue necrosis.

Normally, there's no IMA found in the blood. Increases in IMA are seen within 15 minutes of the onset of ischemia. This is significantly earlier than any other cardiac marker. When the ischemic event is resolved, IMA levels return to normal within several hours. The IMA test is used in conjunction with other cardiac markers, such as troponin, and an electrocardiogram (ECG). If the IMA test is negative and the troponin and ECG are negative, cardiac involvement is ruled out.

NURSING CONSIDERATIONS

·

Inform the patient that he need not restrict food or fluids before the test.

·

Tell the patient that other tests will be performed along with the IMA test.

·

Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately after collection.

·

 

Homocysteine

Homocysteine is an amino acid that's produced by the body. High homocysteine levels can irritate blood vessels, leading to arteriosclerosis. High levels can also raise low-density lipoprotein levels and make blood clot more easily, increasing the risk of blood vessel blockages. In patients with type 2 diabetes, high homocysteine levels are seen when the patient has a decrease in renal function. Normal homocysteine levels are 4 to 17 µmol/L.

NURSING CONSIDERATIONS

·

Perform a venipuncture; collect the sample in a 5-ml tube containing EDTA.

·

Send the specimen to the laboratory immediately after collection in a plastic vial on ice.

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

C-reactive protein

C-reactive protein (CRP) is a substance produced by the liver. A high CRP level indicates that inflammation exists at some location in the body. Other diagnostic tests are needed to determine the location of the inflammation and its cause. Elevated CRP levels can indicate such conditions as:

·

MI

·

 

·

systemic lupus erythematosus

·

postoperative infection

·

trauma

·

heatstroke.

CRP appears in the blood 18 to 24 hours after the onset of tissue damage, and then declines rapidly when the inflammatory process regresses. Some studies have shown a correlation between increased CRP levels and coronary artery disease. Normally, CRP isn't present in the blood; however, levels less than 0.8 mg/dl may be reported as normal.

NURSING CONSIDERATIONS

·

Have the patient withhold fluids, except water, for 8 hours before the test.

·

Perform a venipuncture and collect the sample in a 5-ml nonanticoagulated tube.

·

Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately after collection.

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

B-type natriuretic peptide

B-type natriuretic peptide (BNP) is a hormone polypeptide secreted by ventricular tissues in the heart. The substance is secreted as a response to the increased ventricular volume and pressure that occurs when a patient is in heart failure. It's an excellent hormonal marker of ventricular systolic and diastolic dysfunction.

The normal BNP level in the blood is less than 100 pg/ml. Blood concentrations greater than 100 pg/ml are an accurate predictor of heart failure. The level of BNP in the blood is relative to the severity of heart failure. The higher the level, the worse the symptoms of heart failure. (See Linking BNP levels to heart failure symptom severity.)

NURSING CONSIDERATIONS

·

Perform a venipuncture, and collect the sample in a 5-ml tube containing EDTA.

·

Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately after collection.

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

Atrial natriuretic peptide

Atrial natriuretic peptide (ANP) is a neurohormone similar to BNP that's released by the atria in response to increased atrial pressure. ANP helps:

·

promote sodium excretion

·

inhibit the renin-angiotensin system's effects on aldosterone secretion

·

decrease venous return to the atria, thereby reducing blood pressure and volume.

LINKING BNP LEVELS TO HEART FAILURE SYMPTOM SEVERITY

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pg/ml

Normal levels of ANP are 20 to 77 pg/ml. A patient with overt heart failure will have highly elevated levels of ANP. A patient with cardiovascular disease and elevated cardiac filling pressure but no heart failure will also have increased ANP levels.

NURSING CONSIDERATIONS

·

The patient must fast for 12 hours before the test.

·

Withhold drugs that may interfere with the test, such as beta-adrenergic blockers, diuretics, vasodilators, and cardiac glycosides.

·

Perform a venipuncture and collect the blood in a prechilled potassium-EDTA tube.

·

Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately after collection.

 

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

LIPID STUDIES

Lipid studies include triglycerides, total cholesterol, and lipoprotein fractionation. They measure lipid levels in the body and help evaluate the risk of coronary artery disease.

Triglycerides

Triglycerides are the main storage form of lipids and constitute about 95% of fatty tissue. Monitoring triglyceride levels in the blood helps with early identification of hyperlipidemia and identification of patients at risk for coronary artery disease (CAD).

Triglyceride values are age- and gender-related, and some controversy exists over the most appropriate normal ranges. The most widely accepted normal values are 44 to 180 mg/dl for men and 10 to 190 mg/dl for women.

Triglyceride levels above or below these values suggest a clinical abnormality; for a definitive diagnosis, you'll need additional tests. For example, measuring cholesterol levels may also be necessary, because cholesterol and triglyceride levels vary independently. If both triglyceride and cholesterol levels are high, the patient is at risk for CAD.

NURSING CONSIDERATIONS

·

Because triglycerides are highly affected by a fat-containing meal, with levels rising and peaking 4 hours after ingesting a meal, tell the patient that he should abstain from food for 10 to 14 hours before the test and from alcohol for 24 hours before the test. The patient may drink water.

·

Perform a venipuncture, collect a sample in a 7-ml tube containing EDTA, and send the sample to the laboratory immediately after collection.

·

Avoid prolonged venous occlusion. Remove the tourniquet within 1 minute of application.

Total cholesterol

The total serum cholesterol test measures the circulating levels of the two forms in which cholesterol appears in the body—free cholesterol and cholesterol esters.

For adults, desirable cholesterol levels are less than 200 mg/dl. Levels are considered borderline high up to 240 mg/dl, and high if they're greater than 240 mg/dl. High serum cholesterol levels may be associated with an increased risk for CAD.

NURSING CONSIDERATIONS

·

Fasting isn't needed for isolated cholesterol checks or screening, but fasting is required if total cholesterol is part of a lipid profile. If fasting is required, instruct the patient to abstain from food and drink for 12 hours before the test.

·

Perform a venipuncture, and collect the sample in a 7-ml tube containing EDTA. The patient should be in a sitting position for 5 minutes before the blood is drawn. Fingersticks can also be used for initial screening when using an automated analyzer.

·

Document the drugs the patient is taking.

·

Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately after collection.

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

Lipoprotein fractionation

Lipoprotein fractionation tests are used to isolate and measure the two types of cholesterol in blood: high-density lipoproteins (HDLs) and low-density lipoproteins (LDLs).

The HDL level is inversely related to the risk of CAD—that is, the higher the HDL level, the lower the incidence of CAD. For men, HDL values range from 37 to 70 mg/dl; in women, from 40 to 85 mg/dl.

Conversely, the higher the LDL level, the higher the incidence of CAD. In individuals who don't have CAD, desirable LDL levels are less than 130 mg/dl, borderline high levels are in the range of 130 to 159 mg/dl, and high levels are more than 160 mg/dl.

The American College of Cardiology recommends:

·

HDL levels of 40 mg/dl or higher for men

·

HDL levels of at least 45 mg/dl for women. (HDL levels greater than 60 mg/dl are considered heart healthy for all.)

·

LDL levels of less than 100 mg/dl (Levels of 60 mg/dl or more are considered high.)

Increased HDL levels can occur as a result of long-term aerobic and vigorous exercise. Rarely, a sharp rise (to as high as 100 mg/dl) in a second type of HDL (alpha2-HDL) may signal CAD. (See Predicting CAD with the PLAC test, page 94.)

NURSING CONSIDERATIONS

·

Tell the patient to maintain a normal diet for 2 weeks before the test.

 

·

Tell him to abstain from alcohol for 24 hours before the test.

·

Tell the patient to stop the use of thyroid hormone, hormonal contraceptives, and antilipemics until after the test because they alter results.

·

Perform a venipuncture, and collect the sample in a 7-ml tube containing EDTA.

·

Send the sample to the laboratory immediately after collection to avoid spontaneous redistributions among the lipoproteins. If the sample can't be transported immediately, refrigerate it but don't allow it to freeze.

·

If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

PREDICTING CAD WITH THE PLAC TEST

The PLAC test, a blood test that can help determine who might be at risk for coronary artery disease (CAD), has been approved by the Food and Drug Administration (FDA). The FDA's decision was based on a study of more than 1,300 patients, which was a part of a large multicenter study sponsored by the National Heart, Lung, and Blood Institute.

The PLAC test works by measuring lipoprotein-associated phospholipase A2, an enzyme produced by macrophages, a type of white blood cell. When heart disease is present, macrophages increase production of the enzyme. According to the FDA, an elevated PLAC test result, in conjunction with a low-density-lipoprotein (LDL) cholesterol level of less than 130 mg/dl, generally indicates that a patient has two to three times the risk of coronary heart disease compared to similar patients with lower PLAC test results. The study also found that those people with the highest PLAC test results and LDL cholesterol levels lower than 130mg/dL had the greatest risk of heart disease.

COAGULATION TESTS

Partial thromboplastin time, prothrombin time, international normalized ratio, and activated clotting time are tests that measure clotting time. They're used to measure response to treatment and to screen for clotting disorders.

Partial thromboplastin time

The partial thromboplastin time (PTT) test evaluates all of the clotting factors of the intrinsic pathway except platelets. The test measures the time it takes a clot to form after adding calcium and phospholipid emulsion to a plasma sample. Normally a clot forms 21 to 35 seconds after the reagents are added.

The PTT test also helps monitor a patient's response to heparin therapy. For a patient on anticoagulant therapy, check with the practitioner to find out what PTT results to expect.

NURSING CONSIDERATIONS

·

Tell the patient receiving heparin therapy that this test may be repeated at regular intervals to assess response to treatment.

·

Perform a venipuncture, and collect the sample in a 7-ml tube containing sodium citrate.

·

Completely fill the collection tube, invert it gently several times, and send it to the laboratory on ice.

·

For a patient on anticoagulant therapy, additional pressure may be needed at the venipuncture site to control bleeding.

Prothrombin time

Prothrombin, or factor II, is a plasma protein produced by the liver. The prothrombin time (PT) test (also known as pro time) measures the time required for a clot to form in a citrated plasma sample after the addition of calcium ions and tissue thromboplastin (factor III).

Normally PT ranges from 10 to 14 seconds. In a patient receiving warfarin therapy, the goal of treatment is to attain a PT level 1 to 2.5 times the normal control value.

NURSING CONSIDERATIONS

·

Check the patient's history for use of drugs that may affect test results, such as vitamin K or antibiotics.

·

Perform a venipuncture, and collect the sample in a 7-ml siliconized tube.

·

Completely fill the collection tube, and invert it gently several times to adequately mix the sample and anticoagulant. If the tube isn't filled to the correct volume, an excess of citrate appears in the sample.

International normalized ratio

The international normalized ratio (INR) system is viewed as the best means of standardizing measurement of prothrombin time to monitor oral anticoagulant therapy. It isn't used as a screening test for coagulopathies.

A normal INR in patients receiving warfarin therapy is 2.0 to 3.0. For patients with mechanical prosthetic heart valves, an INR of 2.5 to 3.5 is suggested. Increased INR values may indicate disseminated intravascular coagulation, cirrhosis, hepatitis, vitamin K deficiency, salicylate intoxication, uncontrolled oral anticoagulation, or massive blood transfusion.

NURSING CONSIDERATIONS

·

Tell the patient that the test may be repeated at regular intervals until he reaches his target INR level.

·

Perform a venipuncture and collect the sample in a tube with sodium citrate added.

·

Completely fill the collection tube, and invert it gently several times to adequately mix the sample and anticoagulant. If the tube isn't filled to the correct volume, an excess of citrate appears in the sample.

·

Place the sample on ice and send it to the laboratory immediately after collection.

Activated clotting time, or automated coagulation time, measures the time it takes whole blood to clot.

This test is commonly performed during procedures that require extracorporeal circulation, such as:

·

cardiopulmonary bypass

·

ultrafiltration

·

hemodialysis

·

extracorporeal membrane oxygenation (ECMO).

In a nonanticoagulated patient, the normal activated clotting time is 107 seconds. During cardiopulmonary bypass, heparin is titrated to maintain an activated clotting time between 400 and 600 seconds. During ECMO, heparin is titrated to maintain the activated clotting time between 220 and 260 seconds.

NURSING CONSIDERATIONS

·

Explain to the patient that the test requires a blood sample that's usually drawn from an existing vascular access site; therefore, no venipuncture is necessary.

·

Explain that two samples will be drawn. The first one will be discarded so that heparin in the tubing doesn't interfere with the results.

 

·

 

·

Withdraw 5 to 10 ml of blood from the line and discard it.

·

Withdraw a clean sample of blood into the special tube containing the celite provided with the activated clotting time unit.

·

Turn on the activated clotting time unit, and wait for the signal to insert the tube.

·

Flush the vacular access site according to your facility's protocol.

ELECTROCARDIOGRAPHY

The heart's electrical conduction system can be recorded by using a number of different tests. The most common tests used are a 12-lead electrocardiogram, continuous cardiac monitoring, exercise electrocardiography, Holter monitoring, and signal-averaged electrocardiography.

12-lead electrocardiogram

The 12-lead electrocardiogram (ECG) measures the heart's electrical activity and records it as waveforms. It's one of the most valuable and commonly used diagnostic tools.

The standard 12-lead ECG uses a series of electrodes placed on the patient's extremities and chest wall to assess the heart from 12 different views (leads). The 12 leads include:

·

three bipolar limb leads (I, II, and III)

·

three unipolar augmented limb leads (aVR, aVL, and aVF)

·

six unipolar precordial leads (V1 to V6).

The limb leads and augmented leads show the heart from the frontal plane. The precordial leads show the heart from the horizontal plane. (See Understanding ECG leads, page 98.)

ECG can be used to identify myocardial ischemia and infarction, rhythm and conduction disturbances, chamber enlargement, electrolyte imbalances, and drug toxicity.

NURSING CONSIDERATIONS

·

Use a systematic approach to interpret the ECG recording. (See Visualizing normal ECG waveforms, pages 99 and 100.) Compare the patient's previous ECG with the current one, if available. This will help you identify changes.

·

P waves should be upright; however they may be inverted in lead aVR or biphasic or inverted in leads III, aVL, and V1.

UNDERSTANDING ECG LEADS

Each of the leads on a 12-lead ECG views the heart from a different angle. These illustrations show the direction of electrical activity (depolarization) monitored by each lead and the 12 views of the heart.

 

VIEWS REFLECTED

ON A 12-LEAD ECG

LEAD

VIEW OF THE HEART

 

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STANDARD LIMB LEADS (BIPOLAR)

 

I

lateral wall

 

II

inferior wall

 

III

inferior wall

 

AUGMENTED LIMB LEADS (UNIPOLAR)

 

aVR

no specific view

 

aVL

lateral wall

 

aV

inferior wall

 

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PRECORDIAL, OR CHEST, LEADS (UNIPOLAR)

 

V1

septal wall

 

V2

septal wall

 

V3

anterior wall

 

V4

anterior wall

 

V5

lateral wall

 

V6

lateral wall

·

PR intervals should always be constant, like QRS-complex durations.

         

·

QRS-complex deflections vary in different leads.

·

ST segments should be isoelectric or have minimal deviation.

·

ST-segment elevation greater than 1 mm above the baseline and ST-segment depression greater than 0.5 mm below the baseline are considered abnormal. Leads facing toward an injured area have

ST-segment elevations, and leads facing away show ST-segment depressions.

Each of the 12 standard leads of an electrocardiogram (ECG) takes a different view of heart activity, and each generates its own characteristic tracing. The tracings shown here represent a normal heart rhythm viewed from each of the 12 leads. Keep in mind:

·

An upward (positive) deflection indicates that the wave of depolarization flows toward the positive electrode.

·

A downward (negative) deflection indicates that the wave of depolarization flows away from the positive electrode.

·

An equally positive and negative (biphasic) deflection indicates that the wave of depolarization flows perpendicularly to the positive electrode.

Each lead represents a picture of a different anatomic area; when you find abnormal tracings, compare information from the different leads to pinpoint areas of cardiac damage.

LEAD I

LEAD II

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LEAD III

LEAD aVR

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LEAD aVL

LEAD aVF

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LEAD V1

LEAD V2

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LEAD V3

LEAD V4

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LEAD V5

LEAD V6

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·

The T wave normally deflects upward in leads I, II, and V through V6. It's inverted in lead aVR and variable in the other leads. T-wave changes have many causes and aren't always a reason for alarm. Excessively tall, flat, or inverted T waves occurring with such symptoms as chest pain may indicate ischemia.

·

A normal Q wave generally has a duration of less than 0.04 second. An abnormal Q wave has a duration of 0.04 second or more, a depth greater than 4 mm, or a height one-fourth of the R wave. Abnormal Q waves indicate myocardial necrosis, developing when depolarization can't follow its normal path because of damaged tissue in the area.

·

Remember that aVR normally has a large Q wave, so disregard this lead when searching for abnormal Q waves.

·

The R wave in lead II should be taller than in lead I. The R wave in lead III should be a smaller version of the R wave in lead I. Normally, the R waves get progressively taller from lead V1 to V5 and get slightly smaller in lead V6. (See R-wave progression.)

Continuous cardiac monitoring

Because it allows continuous observation of the heart's electrical activity, cardiac monitoring is used in patients at risk for life-threatening arrhythmias.

Like other forms of electrocardiography, cardiac monitoring uses electrodes placed on the patient's chest to transmit electrical signals that are converted into a cardiac rhythm tracing on an oscilloscope. (See Positioning monitor leads, pages 102 and 103.)

R-WAVE PROGRESSION

R waves should progress normally through the precordial leads. Note that the R wave shown here is the first positive deflection in the QRS complex. Also note that the S wave gets smaller, or regresses, from lead V1 to V6 until it finally disappears.

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Two types of monitoring may be performed: hardwire or telemetry. In hardwire monitoring, the patient is connected to a monitor at the bedside. The rhythm display appears at the bedside, or it may be transmitted to a console at a remote location. Telemetry uses a small transmitter connected to the ambulatory patient to send electrical signals to another location, where they're displayed on a monitor screen. Regardless of the type, cardiac monitors can display the patient's heart rate and rhythm, produce a printed record of cardiac rhythm, and sound an alarm if the heart rate exceeds or falls below specified limits. Monitors also recognize and count abnormal heartbeats as well as changes. (See Identifying cardiac monitor problems, page 104.)

NURSING CONSIDERATIONS

·

Make sure that all electrical equipment and outlets are grounded to avoid electrical shock and interference (artifacts). Also ensure that the patient is clean and dry to prevent electric shock.

·

If the patient's skin is very oily, scaly, or diaphoretic, rub the electrode site with a dry 4″ × 4″ gauze pad before applying the electrode, to help reduce interference in the tracing.

·

Assess skin integrity and reposition the electrodes every 24 hours or as necessary.

·

Document a rhythm strip at least every 8 hours and with any change in the patient's condition (or as stated by your facility's policy).

POSITIONING MONITOR LEADS

This chart shows the correct electrode positions for some of the leads you'll use most often—the five-leadwire, three-leadwire, and telemetry systems. The chart uses the abbreviations RA for the right arm, LA for the left arm, RL for the right leg, LL for the left leg, C for the chest, and G for the ground.

Electrode positions

In the three- and five-leadwire systems, electrode positions for one lead may be identical to those for another lead. When that happens, change the lead selector switch to the setting that corresponds to the lead you want. In some cases, you'll need to reposition the electrodes.

Telemetry

In a telemetry monitoring system, you can create the same leads as the other systems with just two electrodes and a ground wire.

FIVE-LEADWIRE

SYSTEM

THREE-LEADWIRE

SYSTEM

SYSTEM

     

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LEAD III

   

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LEAD MCL1

   

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LEAD MCL6

   

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Exercise electrocardiography

Exercise electrocardiography is a noninvasive test that helps the practitioner assess cardiovascular response to an increased workload. Commonly known as a stress test

An ECG and blood pressure readings are taken while the patient walks on a treadmill or pedals a stationary bicycle, and his response to a constant or increasing workload is observed. Unless complications develop, the test continues until the patient reaches the target heart rate (determined by an established protocol) or experiences chest pain or fatigue.

Stop the test if the patient experiences chest pain, fatigue, or other signs and symptoms that reflect exercise intolerance. These may include:

·

severe dyspnea

·

claudication

·

weakness

·

dizziness

·

hypotension

IDENTIFYING CARDIAC MONITOR PROBLEMS

PROBLEM

POSSIBLE CAUSES

SOLUTIONS

FALSE-HIGH-RATE ALARM

• Monitor interpreting large T waves as QRS complexes, which doubles the rate

• Reposition electrodes to lead where QRS complexes are taller than T waves.

 

• Skeletal muscle activity

• Place electrodes away from major muscle masses.

FALSE-LOW-RATE ALARM

• Shift in electrical axis from patient movement, making QRS complexes too small to register

• Reapply electrodes. Set gain so height of complex is greater than 1 mV.

 

• Low amplitude of QRS

• Increase gain.

 

• Poor contact between electrode and skin

• Reapply electrodes.

ARTIFACT (WAVEFORM INTERFERENCE)

• Patient having seizures, chills, or anxiety

 
 

• Patient movement

• Help the patient relax.

 

• Electrodes applied improperly

• Check electrodes and reapply, if necessary.

 

• Static electricity

• Make sure cables don't have exposed connectors. Change static-causing bedclothes.

 

• Electrical short circuit in leadwires or cable

• Replace broken equipment. Use stress loops when applying leadwires.

 

• Interference from decreased room humidity

• Regulate humidity to 40%.

 

·

pallor

·

vasoconstriction

·

disorientation

·

ataxia

·

ischemic ECG changes (with or without pain)

·

rhythm disturbances

·

heart block

·

ventricular conduction abnormalities.

Because exercise electrocardiography places considerable stress on the heart, it may be contraindicated in the patient with ventricular aneurysm, dissecting aortic aneurysm, uncontrolled arrhythmias, pericarditis, myocarditis, severe anemia, uncontrolled hypertension, unstable angina, or heart failure.

If the patient can't perform physical exercise, a stress test can be performed by I.V. injection of a coronary vasodilator, such as dipyridamole or adenosine. Other methods of stressing the heart include dobutamine administration and pacing (in the patient with a pacemaker).

In normal exercise electrocardiography, the P and T waves, the QRS complex, and the ST segment change minimally; a slight ST-segment depression occurs in some cases, especially in women. The heart rate rises in direct proportion to the workload and metabolic oxygen demand; blood pressure also rises as workload increases. The patient should attain the endurance level predicted by his age and appropriate exercise protocol.

NURSING CONSIDERATIONS

·

Tell the patient not to eat, drink caffeinated beverages, or smoke cigarettes for 4 hours before the test.

·

Explain that he should wear loose, lightweight clothing and snug-fitting, but comfortable shoes, and emphasize that he should immediately report any chest pain, leg discomfort, breathlessness, or fatigue.

·

Check with the practitioner to determine which cardiac drugs should be given or withheld before the test. A beta-adrenergic receptor/blocker, for example, can limit the patient's ability to raise his heart rate.

·

Inform the patient that he may receive an injection of thallium during the test so that the physician can evaluate coronary blood flow. Reassure him that the injection involves negligible radiation exposure.

 

·

Tell the patient that, after the test, his blood pressure and ECG will be monitored for 10 to 15 minutes.

·

Explain that he should wait at least 2 hours before showering and that he should then use warm water.

Signal-averaged electrocardiography

Although a standard 12-lead electrocardiogram (ECG) is obtained on most patients, some may benefit from obtaining a signal-averaged ECG. This simple, noninvasive test helps identify patients at risk for sudden death from sustained ventricular tachycardia.

The test uses a computer to identify late electrical potentials, which are tiny impulses that follow normal depolarization. A standard 12-lead ECG doesn't detect late electrical potentials. Patients who are prone to ventricular tachycardia, or who have had a recent myocardial infarction or unexplained syncope, are good candidates for signal-averaged electrocardiography.

A signal-averaged ECG is a noise-free, surface ECG recording taken from three specialized leads for several hundred heartbeats. (See Placing electrodes for a signal-averaged ECG.) The machine's computer detects late electrical potentials and then enlarges them so they're recognizable.

·

The test is performed by a technician who's specially trained to operate the recording and computer equipment used in analyzing the signal-averaged ECG.

·

Tell the patient to lie as still as possible to avoid distorting the signal.

·

Although the predictive accuracy of a positive signal-averaged ECG is relatively low, it's advocated as a screening test for the patient who should undergo electrophysiologic testing.

Holter monitoring

Also called ambulatory electrocardiography, Holter monitoring allows recording of heart activity as the patient follows his normal routine. Like an exercise electrocardiography, it can provide considerable more diagnostic information than a standard resting electrocardiogram. In addition, Holter monitoring can record intermittent arrhythmias.

This test usually lasts about 24 hours (about 100,000 cardiac cycles). The patient wears a small tape recorder connected to bipolar electrodes placed on his chest and keeps a diary of his activities and associated symptoms.

PLACING ELECTRODES FOR A SIGNAL-AVERAGED ECG

Positioning electrodes for a sign-alaveraged ECG is much different than for a 12-lead ECG. Here's one method:

1. Place the positive X electrode at the left fourth intercostal space, midaxillary line.

2. Place the negative X electrode at the right fourth intercostal space, midaxillary line.

3. Place the positive Y electrode at the left iliac crest.

4. Place the negative Y electrode at the superior aspect of the manubrium of the sternum.

5. Place the positive Z electrode at the fourth intercostal space, left of the sternum.

6. Place the ground (G) on the lower right at the eighth rib.

7. Reposition the patient on his side, or have him sit forward. Then place the negative Z electrode on his back (not shown), directly posterior to the positive Z electrode.

8. Attach all the leads to the electrodes, being careful not to dislodge the posterior lead. Now, you can obtain the tracing.

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NURSING CONSIDERATIONS

·

Urge the patient not to tamper with the monitor or disconnect leadwires or electrodes. Demonstrate how to check the recorder for proper function.

·

Tell the patient that he can't bathe or shower while wearing the monitor. He also needs to avoid electrical appliances, which can interfere with the monitor's recording.

·

Emphasize to the patient the importance of keeping track of his activities, regardless of symptoms.

·

Evaluation of the recordings will guide further treatment.

HEMODYNAMIC MONITORING

Hemodynamic monitoring is used to assess cardiac function and determine the effectiveness of therapy by measuring:

·

cardiac output

USING HEMODYNAMIC MONITORING

Hemodynamic monitoring provides information on intracardiac pressures, arterial pressure, and cardiac output. To understand intracardiac pressures, picture the heart and vascular system as a continuous loop with constantly changing pressure gradients that keep the blood moving. Hemodynamic monitoring records the gradients within the vessels and heart chambers. Cardiac output indicates the amount of blood ejected by the heart each minute.

 

PRESSURE AND

DESCRIPTION

NORMAL

VALUES

CAUSES OF

INCREASED PRESSURE

CAUSES OF

DECREASED PRESSURE

 

CENTRAL VENOUS PRESSURE OR RIGHT ATRIAL PRESSURE

The central venous pressure (CVP) or right atrial pressure (RAP) shows right ventricular function and end-diastolic pressure.

Normal mean pressure ranges from 1 to 6 mm Hg (1.34 to 8 cm H2O).

·

Right-sided heart failure

·

Volume overload

·

 

·

Constrictive pericarditis

·

Pulmonary hypertension

·

Cardiac tamponade

·

Right ventricular infarction

·

Reduced circulating blood volume

 

RIGHT VENTRICULAR PRESSURE

Typically, the physician measures right ventricular pressure only when initially inserting a pulmonary artery catheter. Right ventricular systolic pressure normally equals pulmonary artery systolic pressure; right ventricular end-diastolic pressure, which reflects right ventricular function, equals RAP.

Normal systolic pressure ranges from 20 to 30 mm Hg; normal diastolic pressure, from 0 to 5 mm Hg.

·

 

·

Pulmonary disease

·

Hypoxemia

·

Constrictive pericarditis

·

Chronic heart failure

·

Atrial and ventricular septal defects

·

Patent ductus arteriosus

·

Reduced circulating blood volume

 

PULMONARY ARTERY PRESSURE

Pulmonary artery systolic pressure shows right ventricular function and pulmonary circulation pressures. Pulmonary artery diastolic pressure reflects left ventricular pressures, specifically left ventricular end-diastolic pressure, in a patient without significant pulmonary disease.

Systolic pressure normally ranges from 20 to 30 mm Hg. The mean pressure usually ranges from 10 to 15 mm Hg.

·

Left-sided heart failure

·

Increased pulmonary blood flow (left or right shunting, as in atrial or ventricular septal defects)

·

Any condition causing increased pulmonary arteriolar resistance (such as pulmonary hypertension, volume overload, mitral stenosis, or hypoxia)

·

Reduced circulating blood volume

 

PULMONARY ARTERY WEDGE PRESSURE

Pulmonary artery wedge pressure (PAWP) reflects left atrial and left ventricular pressures, unless the patient has mitral stenosis. Changes in PAWP reflect changes in left ventricular filling pressure.

The mean pressure normally ranges from 6 to 12 mm Hg.

·

Left-sided heart failure

·

Mitral stenosis or insufficiency

·

Pericardial tamponade

·

Reduced circulating blood volume

·

mixed venous blood

           

·

oxygen saturation

·

intracardiac pressures

·

blood pressure. (See Using hemodynamic monitoring.)

Follow your facility's procedure for setting up, zero referencing, calibrating, maintaining, and troubleshooting equipment. Common uses of hemodynamic monitoring include arterial blood pressure monitoring, central venous pressure monitoring, and pulmonary artery pressure monitoring.

Arterial blood pressure monitoring

In arterial blood pressure monitoring, the practitioner inserts a catheter into the radial or femoral artery to measure blood pressure or obtain samples of arterial blood for diagnostic tests such as arterial blood gas (ABG) studies.

A transducer transforms the flow of blood during systole and diastole into a waveform that appears on an oscilloscope. The waveform has five distinct components. (See Types of normal arterial waveforms.)

NURSING CONSIDERATIONS

·

Explain the procedure to the patient and his family, including the purpose of arterial pressure monitoring.

·

Recognizing abnormal arterial waveforms, pages 112 and 113.)

·

Assess the insertion site for signs of infection, such as redness and swelling. Notify the practitioner immediately if these signs appear.

·

Maintain 300 mm Hg pressure in the pressure bag to permit a flush flow of 3 to 6 ml/hour.

·

Document the date and time of catheter insertion, catheter insertion type, type of flush solution used, type of dressing applied, and the patient's tolerance of the procedure.

Central venous pressure monitoring

In central venous pressure (CVP) monitoring, the physician inserts a catheter through a vein and advances it until its tip lies in or near the right atrium. Because no major valves lie at the junction of the vena cava and right atrium, pressure at end diastole reflects back to the catheter. When connected to the transducer or manometer, the catheter measures CVP, an index of right ventricular function.

·

Explain the procedure to the patient and his family, including the purpose of CVP monitoring.

·

After insertion, observe the waveform to assess CVP. (See Differentiating normal from abnormal waveforms, page 114.)

·

Monitor the patient for complications, such as infection, pneumothorax, air embolism, and thrombosis. Notify the practitioner immediately if you notice such complications.

TYPES OF NORMAL ARTERIAL WAVEFORMS

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·

Adhere to your facility's policy for dressing, tubing, catheter, and flush changes.

·

Document the date and time of catheter insertion, catheter insertion site, type of flush solution used, type of dressing applied, and the patient's tolerance of the procedure.

·

Document the CVP readings according to your facility's policy.

RECOGNIZING ABNORMAL ARTERIAL WAVEFORMS

Use this chart to help you recognize and resolve waveform abnormalities.

WAVEFORM

ABNORMALITY

POSSIBLE

CAUSES

NURSING INTERVENTIONS

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Alternating high and low waves in a regular pattern

·

 

·

Check the patient's ECG to confirm ventricular bigeminy. The tracing should reflect premature ventricular contractions every second beat.

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·

Overdamped waveform or hypotensive patient

·

Check the patient's blood pressure with a sphygmomanometer. If you obtain a higher reading, suspect overdamping. Correct the problem by trying to aspirate the arterial line. If you succeed, flush the line. If the reading is very low or absent, suspect hypotension.

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Slightly rounded waveform with consistent variations in systolic height

·

Patient on ventilator with positive end-expiratory pressure

·

Check the patient's systolic blood pressure regularly. The difference between the highest and lowest systolic pressure reading should be less than 10 mm Hg. If the difference exceeds that amount, suspect pulsus paradoxus, possibly from cardiac tamponade.

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Slow upstroke

·

Aortic stenosis

·

Check the patient's heart sounds for signs of aortic stenosis. Also notify the practitioner, who will document suspected aortic stenosis in his notes.

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Diminished amplitude on inspiration

·

Pulsus paradoxus, possibly from cardiac tamponade, constrictive pericarditis, or lung disease

·

Note systolic pressure during inspiration and expiration. If inspiratory pressure is at least 10 mm Hg less than expiratory pressure, call the practitioner.

·

If you're also monitoring pulmonary artery pressure, observe for a diastolic plateau. This abnormality occurs when the mean central venous pressure (right atrial pressure), mean pulmonary artery pressure, and mean pulmonary artery wedge pressure (pulmonary artery obstructive pressure) are within 5 mm Hg of one another.

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Alteration in beat-to-beat amplitude (in otherwise normal rhythm)

·

Pulsus alternans, which may indicate left ventricular failure

·

Observe the patient's ECG, noting any deviation in the waveform.

·

Notify the practitioner if this is a new and sudden abnormality.

Pulmonary artery pressure monitoring

Continuous pulmonary artery pressure (PAP) and intermittent pulmonary artery wedge pressure (PAWP) measurements provide important information about left ventricular function and preload. (See Understanding pulmonary artery pressures, page 115.) Use this information for monitoring and for aiding diagnosis, refining assessment, guiding interventions, and projecting patient outcomes.

P.113

PAP monitoring is indicated for patients who:

·

are hemodynamically unstable

·

need fluid management or continuous cardiopulmonary assessment

·

are receiving multiple or frequently administered cardioactive drugs.

DIFFERENTIATING NORMAL FROM ABNORMAL CVP WAVEFORMS

These illustrations show a normal central venous pressure (CVP) waveform and abnormal CVP waveforms, along with possible causes of abnormal waveforms.

Normal waveforms

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Elevated a wave

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Physiologic causes

·

Increased resistance to ventricular filling

·

Increased atrial contraction

Associated conditions

·

Heart failure

·

Tricuspid stenosis

·

Pulmonary hypertension

Elevated v wave

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Physiologic cause

·

Regurgitating flow

Associated conditions

·

Tricuspid insufficiency

·

Inadequate closure of the tricuspid valve due to heart failure

Absent a wave

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Physiologic cause

·

Decreased or absent atrial contraction

Associated conditions

·

Atrial fibrillation

·

Junctional arrhythmias

·

Ventricular pacing

Elevated a and v waves

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Physiologic causes

·

Increased resistance to ventricular filling, which causes an elevated a wave

·

Functional regurgitation, which causes an elevated v

Associated conditions

·

y descent than x descent)

·

Constrictive pericardial disease (y descent exceeds  descent)

·

Heart failure

·

Hypervolemia

·

Atrial hypertrophy

UNDERSTANDING PULMONARY ARTERY PRESSURES

PA systolic pressure

Pulmonary artery (PA) systolic pressure measures right ventricular systolic ejection or, simply put, the amount of pressure needed to open the pulmonic valve and eject blood into the pulmonary circulation. When the pulmonic valve is open, PA systolic pressure should be the same as right ventricular pressure.

PA diastolic pressure

PA diastolic pressure represents the resistance of the pulmonary vascular bed as measured when the pulmonic valve is closed and the tricuspid valve is open. To a limited degree (under absolutely normal conditions), PA diastolic pressure also reflects left ventricular end-diastolic pressure.

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PAP monitoring is also crucial for patients experiencing shock, trauma, pulmonary or cardiac disease, or multiple organ dysfunction syndrome.

A pulmonary artery (PA) catheter has up to six lumens that gather hemodynamic information. In addition to distal and proximal lumens used to measure CVP and PAP, a PA catheter has a balloon inflation lumen that inflates the balloon for PAWP measurement and a thermistor connector lumen that allows cardiac output measurement.

DIFFERENTIATING PULMONARY ARTERY CATHETER PORTS

A pulmonary artery (PA) catheter contains several lumen ports to allow various catheter functions:

·

The balloon inflation lumen inflates the balloon at the distal tip of the catheter for pulmonary artery wedge pressure (PAWP) measurement.

·

A distal lumen measures PA pressure when connected to a transducer and measures PAWP during balloon inflation. It also permits drawing of mixed venous blood samples.

·

A proximal lumen measures right atrial pressure (central venous pressure).

·

The thermistor connector lumen contains temperature-sensitive wires, which feed information into a computer for cardiac output calculation.

·

Another lumen may provide a port for pacemaker electrodes or measurement of mixed venous oxygen saturation (S[v with bar above]O2

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Some catheters also have a pacemaker wire lumen that provides a port for pacemaker electrodes and measures continuous mixed venous oxygen saturation. (See .)

The physician inserts the balloon-tipped, multilumen catheter into the patient's internal jugular or subclavian vein. When the catheter reaches the right atrium, the balloon is inflated to float the catheter through the right ventricle into the pulmonary artery. This permits PAWP measurement through an opening at the catheter's tip.

The deflated catheter rests in the pulmonary artery, allowing diastolic and systolic PAP readings. The balloon should be totally deflated except when taking a PAWP reading because prolonged wedging can cause pulmonary infarction. (See Observing pulmonary artery waveforms, page 118.)

NURSING CONSIDERATIONS

·

Inform the patient that he'll be conscious during catheterization, and that he may feel temporary local discomfort from the administration of the local anesthetic. Catheter insertion takes about 15 to 30 minutes.

·

After catheter insertion, you may inflate the balloon with a syringe to take PAWP readings. Be careful not to inflate the balloon with more than 1.5 cc of air. Overinflation could distend the pulmonary artery causing vessel rupture. Don't leave the balloon wedged for a prolonged period because this could lead to a pulmonary infarction.

·

After each PAWP reading, flush the line; if you encounter difficulty, notify the practitioner.

·

Maintain 300 mm Hg pressure in the pressure bag to permit a flush flow of 3 to 6 ml/hour.

·

If fever develops when the catheter is in place, inform the practitioner. He may remove the catheter and send its tip to the laboratory for culture.

·

Make sure stopcocks are properly positioned and connections are secure. Loose connections may introduce air into the system or cause blood backup, leakage of deoxygenated blood, or inaccurate pressure readings. Also make sure the lumen hubs are properly identified to serve the appropriate catheter ports. (See Identifying hemodynamic pressure monitoring problems, pages 119 and 120.)

·

Because the catheter can slip back into the right ventricle and irritate it, check the monitor for a right ventricular waveform to detect this problem promptly. Running a continuous infusion through the distal lumen will interfere with your ability to monitor this waveform for changes.

·

To minimize vascular trauma, make sure the balloon is deflated whenever the catheter is withdrawn from the pulmonary artery to the right ventricle or from the right ventricle to the right atrium.

OBSERVING PULMONARY ARTERY WAVEFORMS

During pulmonary artery catheter insertion, the waveforms on the monitor change as the catheter advances through the heart.

Right atrium

When the catheter tip enters the right atrium, the first heart chamber on its route, a waveform like the one shown below appears on the monitor. Note the two small upright waves. The a waves represent the right ventricular end-diastolic pressure; the v waves, right atrial filling.

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Right ventricle

As the catheter tip reaches the right ventricle, you'll see a waveform with sharp systolic upstrokes and lower diastolic dips, as shown below.

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Pulmonary artery

The catheter then floats into the pulmonary artery, causing a pulmonary artery pressure (PAP) waveform such as the one shown below. Note that the upstroke is smoother than on the right ventricle waveform. The dicrotic notch indicates pulmonic valve closure.

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PAWP

Floating into a distal branch of the pulmonary artery, the balloon wedges where the vessel becomes too narrow for it to pass. The monitor now shows a pulmonary artery wedge pressure (PAWP) waveform, with two small upright waves, as shown below. The a wave represents left ventricular end-diastolic pressure; the v wave, left atrial filling. The balloon is then deflated, and the catheter is left in the pulmonary artery.

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IDENTIFYING HEMODYNAMIC PRESSURE MONITORING PROBLEMS

PROBLEM

POSSIBLE

CAUSES

INTERVENTIONS

LINE FAILS TO FLUSH

·

Stopcocks positioned incorrectly

·

Make sure the stopcocks are positioned correctly.

 

·

Inadequate pressure from pressure bag

·

Make sure the pressure bag gauge reads 300 mm Hg.

 

·

 

·

Check the pressure tubing for kinks.

 

·

Blood clot in catheter

·

Try to aspirate the clot with a syringe. If the line still won't flush, notify the practitioner and prepare to replace the line. Important: Never use a syringe to flush a hemodynamic line.

DAMPED WAVEFORM

·

Air bubbles

·

Secure all connections.

·

Remove air from the lines and the transducer.

·

Check for and replace cracked equipment.

 

·

Blood clot in catheter

·

Refer to “Line fails to flush” (above).

 

·

Blood flashback in line

·

Make sure stopcock positions are correct; tighten loose connections and replace cracked equipment; flush the line with the fast-flush valve; replace the transducer dome if blood backs up into it.

 

·

Incorrect transducer position

·

Make sure the transducer is kept at the level of the right atrium at all times. Improper levels give false-high or false-low pressure readings.

 

·

Arterial catheter out of blood vessel or pressed against vessel wall

·

Reposition the catheter if it's against the vessel wall.

·

Try to aspirate blood to confirm proper placement in the vessel. If you can't aspirate blood, notify the practitioner and prepare to replace the line. Note: Bloody drainage at the insertion site may indicate catheter displacement. Notify the practitioner immediately.

PULMONARY ARTERY WEDGE PRESSURE TRACING UNOBTAINABLE

·

Ruptured balloon

·

If you feel no resistance when injecting air or if you see blood leaking from the balloon inflation lumen, stop injecting air and notify the practitioner. If the catheter is left in, label the inflation lumen with a warning not to inflate.

 

·

Incorrect amount of air in balloon

·

Catheter malpositioned

·

Deflate the balloon. Check the label on the catheter for correct volume. Reinflate slowly with the correct amount. To avoid rupturing the balloon, never use more than the stated volume.

·

Notify the practitioner. Obtain a chest X-ray.

 

·

Adhere to your facility's policy for dressing, tubing, catheter, and flush changes.

·

Document the date and time of catheter insertion, the physician who performed the procedure, the catheter insertion site, pressure waveforms and values for the various heart chambers, balloon inflation volume required to obtain a wedge tracing, arrhythmias that occurred during or after the procedure, type of flush solution used and its heparin concentration (if any), type of dressing applied, and the patient's tolerance of the procedure.

A CLOSER LOOK AT THE THERMODILUTION METHOD

This illustration shows the path of the injectate solution through the heart during thermodilution cardiac output monitoring.

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Cardiac output monitoring

Cardiac output, the amount of blood ejected by the heart in 1 minute, is monitored to evaluate cardiac function. The normal range for cardiac output is 4 to 8 L/minute.

The most widely used method for monitoring cardiac output is the bolus thermodilution technique. (See A closer look at the thermodilution method.) Other methods include the Fick method and the dye dilution test. (See Calculating cardiac output.) To measure cardiac output, a solution is injected into the right atrium through a port on a PA catheter. Iced or room-temperature injectant may be used depending on your facility's policy and on the patient's status.

CALCULATING CARDIAC OUTPUT

One way to calculate cardiac output is by using the Fick method. In this method, the blood's oxygen content is measured before and after it passes through the lungs. First, blood is removed from the pulmonary and brachial arteries and analyzed for oxygen content. Next, a spirometer is used to measure oxygen consumption (the amount of air entering the lungs each minute).

Use this formula to calculate cardiac output:

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This indicator solution mixes with the blood as it travels through the right ventricle into the pulmonary artery, and a thermistor on the catheter registers the change in temperature of the flowing blood. A computer then plots the temperature change over time as a curve and calculates flow based on the area under the curve. (See Analyzing thermodilution curves.)

Cardiac output is better assessed by calculating cardiac index, which takes body size into account. To calculate the patient's cardiac index, divide his cardiac output by his body surface area, a function of height and weight. The normal cardiac index for adults ranges from 2.5 to 4.2 L/minute/m2; for pregnant women, it ranges from 3.5 to 6.5 L/minute/m2, page 125.)

NURSING CONSIDERATIONS

·

Make sure the patient doesn't move during the procedure because movement can cause an error in measurement.

ANALYZING THERMODILUTION CURVES

The thermodilution curve provides valuable information about cardiac output, injection technique, and equipment problems. When studying the curve, keep in mind that the area under the curve is inversely proportionate to cardiac output: The smaller the area under the curve, the higher the cardiac output; the larger the area under the curve, the lower the cardiac output.

Besides providing a record of cardiac output, the curve may indicate problems related to technique, such as erratic or slow injectate instillations, or other problems, such as respiratory variations or electrical interference. The curves below correspond to those typically seen in clinical practice.

Normal thermodilution curve

With an accurate monitoring system and a patient who has adequate cardiac output, the thermodilution curve begins with a smooth, rapid upstroke and is followed by a smooth, gradual downslope. The curve shown below indicates that the injectate instillation time was within the recommended 4 seconds and that the temperature curve returned to baseline blood temperature.

The height of the curve may vary, depending on whether you use a room-temperature or an iced injectate. Room-temperature injection produces an upstroke of lower amplitude.

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Low cardiac output curve

A thermodilution curve representing low cardiac output shows a rapid, smooth upstroke (from proper injection technique). However, because the heart is ejecting blood less efficiently from the ventricles, the injectate warms slowly and takes longer to be ejected from the ventricle. Consequently, the curve takes longer to return to baseline. This slow return produces a larger area under the curve, corresponding to low cardiac output.

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High cardiac output curve

Again, the curve has a rapid, smooth upstroke from proper injection technique. But because the ventricles are ejecting blood too forcefully, the injectate moves through the heart quickly and the curve returns to baseline more rapidly. The smaller area under the curve suggests higher cardiac output.

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Curve reflecting poor technique

This curve results from an uneven and too slow (taking more than 4 seconds) administration of injectate. The uneven and slower than normal upstroke and the larger area under the curve erroneously indicate low cardiac output. A kinked catheter, unsteady hands during the injection, or improper placement of the injectate lumen in the introducer sheath may also cause this type of curve.

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Curve associated with respiratory variations

To obtain a reliable cardiac output measurement, you need a steady baseline pulmonary artery blood temperature. If the patient has rapid or labored respirations or if he's receiving mechanical ventilation, the thermodilution curve may reflect inaccurate cardiac output values. The curve shown below from a patient receiving mechanical ventilation reflects fluctuating pulmonary artery blood temperatures. The thermistor interprets the unsteady temperature as a return to baseline. The result is a curve erroneously showing a high cardiac output (small area under the curve). (Note: In some cases, the equipment senses no return to baseline at all and produces a sinelike curve recorded by the computer as 0.00).

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·

Perform cardiac output measurements and monitoring at least every 2 to 4 hours, especially if the patient is receiving vasoactive or inotropic agents or if fluids are being added or restricted.

     

·

Discontinue cardiac output measurements when the patient is hemodynamically stable and weaned from his vasoactive and inotropic medications.

·

Monitor the patient for signs and symptoms of inadequate perfusion, including restlessness, fatigue, changes in level of consciousness, decreased capillary refill time, diminished peripheral pulses, oliguria, and pale, cool skin.

·

Add the fluid volume injected for cardiac output determinations to the patient's total intake.

 

·

Record the patient's cardiac output, cardiac index, and other hemodynamic values and vital signs at the time of measurement. Note the patient's position during measurement.

MEASURING CARDIAC FUNCTION

Listed below are several common measures of cardiac function that are based on information obtained from a pulmonary artery catheter. Most cardiac output (CO) systems will compute these values automatically.

 

NORMAL

VALUES

FORMULA

FOR

CALCULATION

CAUSES OF

INCREASED

VALUES

CAUSES OF

DECREASED

VALUES

Stroke volume (SV)—Volume of blood pumped by the ventricle in one contraction

60 to 130 ml/beat

SV= CO × 1,000/HR

Sepsis Hypervolemia Inotrope administration

 

Stroke volume index (SVI)—Determines if the SV is adequate for patient's body size

30 to 65 ml/beat/m2

or SVI= CI/HR

Same as SV

Same as SV

Systemic vascular resistance (SVR)—degree of left ventricular resistance, or afterload

800 to 1,400 dynes/sec/cm-5

SVR= MAP-CVP/CO × 80

Hypothermia Hypovolemia Vasoconstriction

Vasodilation Vasodilators Shock (anaphylactic, neurogenic, or septic)

Pulmonary vascular resistance (PVR)

20 to 200 dynes/sec/cm-

PVR= MPAP-PAWP/CO × 80

 

Pulmonary vasodilating drugs (morphine)

Key:

HR-heart rate BSA-body surface area CI-cardiac index

MAP-mean arterial pressure CVP-central venous pressure MPAP-mean pulmonary artery pressure

PAWP-pulmonary artery wedge pressure

CATHETERIZATION STUDIES

Catheterization studies use a catheter inserted through either an artery or a vein to go into the heart and examine the coronary arteries, the heart structure, or determine the location of arrhythmias. Two types of catheter studies are cardiac catheterization and the electrophysiology study.

Cardiac catheterization

Cardiac catheterization involves passing a catheter into the right, left, or both sides of the heart. (See Differentiating right- and left-side heart catheterization.)

This procedure permits measurement of blood pressure and blood flow in the chambers of the heart. It's used to determine valve competence and cardiac wall contractility and to detect intracardiac shunts. The procedure is also used for blood sample collection and can be used to obtain diagnostic films of the ventricles (contrast ventriculography) and arteries (coronary arteriography or angiography).

Use of thermodilution catheters allows calculation of cardiac output. Such calculations are used to evaluate valvular insufficiency or stenosis, septal defects, congenital anomalies, myocardial function and blood supply, and heart wall motion.

Common abnormalities and defects that can be confirmed by cardiac catheterization include:

·

coronary artery disease

·

myocardial incompetence

·

valvular heart disease

·

septal defects.

NURSING CONSIDERATIONS

When caring for a patient undergoing a cardiac catheterization, describe the procedure and events after it and take steps to prevent post-operative complications.

Before the procedure

·

Explain that this test is used to evaluate the function of the heart and its vessels. Instruct the patient to restrict food and fluids for at least 6 hours before the test. Tell him that the procedure takes 1 to

2 hours and that he may receive a mild sedative during the procedure.

DIFFERENTIATING RIGHT- AND LEFT-SIDE HEART CATHETERIZATION

In catheterization of the left side of the heart, a catheter is inserted into an artery in the antecubital fossa or into the left femoral artery. Left-sided heart catheterization assesses the patency of the coronary arteries, mitral and aortic valve function, and left ventricular function. It aids in the diagnosis of left ventricular enlargement, aortic stenosis and insufficiency aortic root enlargement, mitral insufficiency, aneurysm, and intracardiac shunt.

In catheterization of the right side of the heart, the catheter is inserted into an antecubital vein or the femoral vein and advanced through the inferior vena cava or right atrium. Right-sided heart catheterization assesses tricuspid and pulmonic valve function and pulmonary artery pressures.

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·

Tell the patient that the catheter is inserted into an artery or vein in the arm or leg. Tell him that he'll experience a transient stinging sensation when a local anesthetic is injected to numb the incision site for catheter insertion.

·

Inform the patient that injection of the contrast medium through the catheter may produce a hot, flushing sensation or nausea that quickly passes; instruct him to follow directions to cough or breathe deeply. Explain that he'll be given medication if he experiences chest pain during the procedure. Explain that he may also be given nitroglycerin periodically to dilate coronary vessels and aid visualization. Reassure him that complications, such as myocardial infarction and thromboembolism, are rare.

·

Make sure that the patient or a responsible family member has signed a consent form.

·

Check for and tell the practitioner about hypersensitivity to shellfish, iodine, or contrast media used in other diagnostic tests.

·

Discontinue anticoagulant therapy to reduce the risk of complications from bleeding.

·

Review activity restrictions and position requirements that may be necessary for the patient after the procedure, such as lying flat with the limb extended for 4 to 6 hours and using sandbags to apply pressure to the insertion site if a femoral sheath is used.

·

Document the presence of peripheral pulses, noting their intensity. Mark the pulses so they may be easily located after the procedure.

After the procedure

·

Determine if a hemostatic device, such as a collagen plug or suture closure system, was used to close the vessel puncture site. If either method was used, inspect the site for bleeding or oozing, redness, swelling, or hematoma formation. Maintain the patient on bed rest for 1 to 2 hours.

·

Enforce bed rest for 8 hours if no hemostatic device was used. If the femoral route was used for catheter insertion, keep the patient's leg extended for 6 to 8 hours; if the antecubital fossa route was used, keep the arm extended for at least 3 hours.

·

Monitor vital signs every 15 minutes for 2 hours, then every 30 minutes for 2 hours, and then every hour for 4 hours. If no hematoma or other problems arise, check every 4 hours. If vital signs are unstable, check every 5 minutes and notify the practitioner.

 

·

Continually assess the insertion site for a hematoma or blood loss, and reinforce the pressure dressing as needed.

·

Check the patient's color, skin temperature, and peripheral pulse below the puncture site.

·

 

·

Watch for signs of chest pain, shortness of breath, abnormal heart rate, dizziness, diaphoresis, nausea or vomiting, or extreme fatigue. Notify the practitioner immediately if these complications occur.

Electrophysiology studies

Electrophysiology studies record electrical conduction during slow withdrawal of a bipolar or tripolar electrode catheter from the right ventricle through the bundle of His to the sinoatrial node. The catheter is introduced into the femoral vein, passing through the right atrium and across the septal leaflet of the tricuspid valve.

Normal conduction intervals in adults are as follows: HV interval, 35 to 55 msec; AH interval, 45 to 150 msec; and PA interval, 20 to 40 msec.

NURSING CONSIDERATIONS

When caring for a patient undergoing an electrophysiology study, describe the procedure and events after it and take steps to prevent post-operative complications.

Before the procedure

·

Explain that this test is used to evaluate the heart's conduction system. Instruct the patient to restrict food and fluids for at least 6 hours before the test. Tell him that the procedure takes 1 to 3 hours and that he may receive a mild sedative during the procedure.

·

Tell the patient that the catheter is inserted into an artery in the leg. Tell him that he'll experience a transient stinging sensation when a local anesthetic is injected to numb the incision site for catheter insertion.

·

Have the patient void before the test.

·

 

·

Review activity restrictions and position requirements that may be necessary for the patient after the procedure, such as lying flat with the limb extended for 4 to 6 hours and using sandbags to apply pressure to the insertion site.

 

·

 

After the procedure

·

Determine if a hemostatic device, such as a collagen plug or suture closure system, was used to close the vessel puncture site. If either method was used, inspect the site for bleeding or oozing, redness, swelling, or hematoma formation. Maintain the patient on bed rest for 1 to 2 hours.

·

Enforce bed rest for 8 hours if no hemostatic device was used. If the femoral route was used for catheter insertion, keep the patient's leg extended for 6 to 8 hours; if the antecubital fossa route was used, keep the arm extended for at least 3 hours.

·

Monitor vital signs every 15 minutes for 2 hours, then every 30 minutes for 2 hours, and then every hour for 4 hours. If no hematoma or other problems arise, check every 4 hours. If vital signs are unstable, check every 5 minutes and notify the practitioner.

·

Continually assess the insertion site for a hematoma or blood loss, and reinforce the pressure dressing as needed.

·

Check the patient's color, skin temperature, and peripheral pulse below the puncture site.

·

Obtain a 12-lead electrocardiogram to assess for changes.

·

Watch for signs of chest pain, shortness of breath, abnormal heart rate, dizziness, diaphoresis, nausea or vomiting, or extreme fatigue. Notify the practitioner immediately if these complications occur.

Imaging and radiographic testing allows for detailed images of the heart and its ability to function. These tests include echocardiography, cardiac magnetic resonance imaging, cardiac positron emission tomography, cardiac blood pool imaging, technetium-99m pyrophosphate scanning, cardiac scoring computed tomography, thallium scanning, Doppler ultrasonography, and venography.

Echocardiography

Echocardiography is used to examine the size, shape, and motion of cardiac structures. In this procedure, a transducer is placed at an acoustic window (an area where bone and lung tissue are absent) on the patient's chest. The transducer directs sound waves toward cardiac structures, which reflect these waves.

The transducer picks up the echoes, converts them to electrical impulses, and relays them to an echocardiography machine for display on a screen and for recording on a strip chart or videotape. The most commonly used echocardiographic techniques are M-mode (motion mode) and two-dimensional.

In M-mode echocardiography, a single, pencil-like ultrasound beam strikes the heart, producing an “ice pick,” or vertical, view of cardiac structures. This mode is especially useful for precisely viewing cardiac structures.

In two-dimensional echocardiography, the ultrasound beam rapidly sweeps through an arc, producing a cross-sectional, or fanshaped, view of cardiac structures; this technique is useful for recording lateral motion and providing the correct spatial relationship between cardiac structures. In many cases, both techniques are performed to complement each other.

Doppler echocardiography may be used to assess speed and direction of blood flow. The sound of blood flow may be heard as the continuous-wave and pulse-wave Doppler sampling of cardiac valves is performed. This technique is used primarily to assess heart sounds and murmurs as they relate to cardiac hemodynamics.

In exercise echocardiography and dobutamine stress echocardiography, a two-dimensional echocardiogram records cardiac wall motion during exercise or while dobutamine is being infused. (See Teaching about cardiac stress testing, pages 132 and .)

The echocardiogram may detect mitral stenosis, mitral valve prolapse, aortic insufficiency, wall motion abnormalities, and pericardial effusion.

NURSING CONSIDERATIONS

·

Explain the procedure to the patient, and advise him to remain still during the test because movement can distort results. Tell him that conductive gel is applied to the chest and a quarter-sized transducer is placed directly over the gel. Because pressure is exerted to keep the transducer in contact with the skin, warn the patient that he may feel minor discomfort.

·

After the procedure, remove the conductive gel from the skin.

Transesophageal echocardiography

Transesophageal echocardiography combines ultrasound with endoscopy to give a better view of the heart's structures. A small transducer is attached to the end of a gastroscope and inserted into the esophagus, allowing images to be taken from the posterior aspect of the heart. This causes less tissue penetration and interference from chest wall structures and produces high-quality images of the thoracic aorta, except for the superior ascending aorta, which is shadowed by the trachea.

TEACHING ABOUT CARDIAC STRESS TESTING

Exercise echocardiography and dobutamine stress echocardiography are types of cardiac stress testing that detect changes in heart wall motion through the use of two-dimensional echocardiography during exercise or a dobutamine infusion. Imaging is done before and after either exercise or dobutamine administration. Usually, these tests are performed to:

·

identify the cause of chest pain

·

detect heart abnormalities, obstructions, or damage

·

determine the heart's functional capacity after myocardial infarction or cardiac surgery

·

evaluate myocardial perfusion

·

measure the heart chambers

·

set limits for an exercise program.

Preparing your patient

When preparing your patient for these tests, cover the following points:

·

Explain that this test will evaluate how his heart performs under stress and how specific heart structures work under stress.

·

Instruct the patient not to eat, smoke, or drink alcohol or caffeinated beverages for at least 4 hours before the test.

·

Advise him to ask his practitioner whether he should withhold current medications before the test.

·

Tell him to wear a two-piece outfit because he'll be removing all clothing above the waist and will wear a hospital gown.

·

Explain that electrodes will be placed on his chest and arms to obtain an initial electrocardiogram (ECG). Mention that the areas where electrodes are placed will be cleaned with alcohol and that the skin will be abraded for optimal electrode contact.

·

Tell him that an initial echocardiogram will be performed while he's lying down. Conductive gel, which feels warm, will be placed on his chest. Then a special transducer will be placed at various angles on his chest to visualize different parts of his heart. Emphasize that he must remain still to prevent distorting the images.

·

Inform the patient that the entire procedure should take 60 to 90 minutes. Explain that the practitioner will compare these echocardiograms to diagnose his heart condition.

Explaining exercise echocardiography

If the patient will have an exercise stress test after the initial echocardiogram, cover these teaching points:

·

Tell him that he'll walk on the treadmill at a prescribed rate for a predetermined time to raise his heart rate. After he reaches the prescribed heart rate, he'll lie down and a second echocardiogram will be done.

·

 

·

Reassure him that his blood pressure will be monitored during the test. After the test is complete, his ECG and blood pressure will be monitored for 10 minutes.

Describing the dobutamine stress test

If the patient will undergo a dobutamine stress test after the initial echocardiogram, cover these teaching points:

·

Explain that an I.V. line will be inserted into his vein for the dobutamine infusion. Tell him that this drug will increase his heart rate without exercise. Tell him to expect initial discomfort when the I.V. line is inserted. Mention that, during the infusion, he may feel palpitations, shortness of breath, and fatigue.

·

Inform the patient that a second echocardiogram will be done during the dobutamine infusion. After the drug is infused and his heart rate reaches the desired level, a third echocardiogram will be obtained.

·

Reassure the patient that his blood pressure will be monitored during the test.

NURSING CONSIDERATIONS

·

Explain to the patient that this test will allow better visualization of heart function and structures.

·

Instruct the patient to fast for 6 hours before the test.

·

Have the patient remove any dentures or oral prostheses and note any loose teeth.

·

Make sure the patient or a responsible family member has signed an informed consent form.

 

·

During the procedure, vasovagal responses may occur with gagging, so closely observe the cardiac monitor.

·

After the procedure, don't give the patient food or water until his gag reflex has returned.

Cardiac blood pool imaging

Cardiac blood pool imaging evaluates ventricular performance after the injection of human serum albumin or red blood cells tagged with technetium 99m. A camera records the radioactivity of the isotope while it passes through the left ventricle. A computer is then used to calculate the ejection fraction based on the amount of isotope ejected during each beat; the presence and size of intracardiac shunts can also be determined.

Gated cardiac blood pool imaging uses the camera to record 500 to 1,000 cardiac cycles and determine areas of hypokinesia or akinesia.

Multiple-gated acquisition scanning uses sequential images to evaluate wall motion and determine the ejection fraction and other indices of cardiac function.

NURSING CONSIDERATIONS

·

Tell the patient that he will receive an I.V. injection of a radioactive tracer, but that the tracer poses no radiation hazard and rarely produces adverse effects.

·

Make sure the patient or a responsible family member has signed an informed consent form.

Cardiac magnetic resonance imaging

Also known as nuclear magnetic resonance, cardiac magnetic resonance imaging (MRI) yields high-resolution, tomographic, three-dimensional images of body structures. It takes advantage of certain magnetically aligned body nuclei that fall out of alignment after radio frequency transmission. The MRI scanner records the signals the nuclei emit as they realign in a process called precession and then translates the signals into detailed pictures of body structures. The resulting images show tissue characteristics without lung or bone interference.

A cardiac MRI permits visualization of valve leaflets and structures, pericardial abnormalities and processes, ventricular hypertrophy, cardiac neoplasm, infarcted tissue, anatomic malformations, and structural deformities. It can be used to monitor the progression of ischemic heart disease and the effectiveness of treatment.

NURSING CONSIDERATIONS

·

Instruct the patient that he'll need to lie still during the test.

·

Warn the patient that he'll hear a thumping noise.

·

Have the patient remove all jewelry and other metallic objects before testing. A patient with an internal surgical clip, scalp vein needle, pacemaker, gold fillings, heart valve prosthesis, or other metal objects in his body can't undergo an MRI.

·

Permit the patient to resume activities as indicated.

Cardiac positron emission tomography

Cardiac positron emission tomography (PET) scanning combines elements of computed tomography scanning and conventional radionuclide imaging.

Radioisotopes are given to the patient by injection, inhalation, or I.V. infusion. One isotope targets blood; one targets glucose. The isotopes emit particles called positrons. The PET scanner detects and reconstructs the positron to form an image.

A PET scan shows coronary blood flow and glucose metabolism. A decrease in blood flow with a corresponding increase in glucose metabolism indicates ischemia; a decrease in blood flow with a decrease in glucose metabolism indicates necrotic or scarred heart tissue.

NURSING CONSIDERATIONS

·

Tell the patient that he may be given the isotope by injection, inhalation, or I.V. infusion.

·

Stress the importance of remaining still during the test.

·

After the test, encourage the patient to increase his fluid intake to help flush the isotope from his bladder.

Cardiac scoring computed tomography

Cardiac scoring computed tomography is a series of tomograms that provide cross-sectional images of the heart. These images are used to reconstruct the horizontal, sagittal, and coronal planes of the heart.

This test helps determine the calcium content in the coronary arteries. Increased calcium content in the coronary arteries indicates an increased risk of myocardial infarction or critical narrowing of the arteries and further testing is indicated.

NURSING CONSIDERATIONS

·

Stress the importance of remaining still during the test.

·

Tell the patient that he may hear clacking sounds during the test, and reassure him that this is normal.

Technetium-99m pyrophosphate scanning

99mTc) pyrophosphate scanning, also known as hot spot imaging or pyrophosphate scanning, helps diagnose acute myocardial injury by showing the location and size of newly damaged myocardial tissue. Especially useful for diagnosing transmural infarction, this test works best when performed 12 hours to 6 days after symptom onset. It also helps diagnose right ventricular infarctions; locate true posterior infarctions; assess trauma, ventricular aneurysm, and heart tumors; and detect myocardial damage from a recent electric shock such as defibrillation.

In this test, the patient receives an injection of 99mTc pyrophosphate, a radioactive material absorbed by injured cells. A scintillation camera scans the heart and displays damaged areas as “hot spots” or bright areas. A spot's size usually corresponds to the injury size.

NURSING CONSIDERATIONS

·

Tell the patient that the practitioner will inject 99mTc pyrophosphate into an arm vein about 3 hours before the start of this

45-minute test. Reassure him that the injection causes only transient discomfort and that it involves only negligible radiation exposure.

·

Instruct the patient to remain still during the test.

·

Permit the patient to resume activities, as indicated.

UNDERSTANDING THALLIUM SCANNING

In thallium scanning, areas with poor blood flow and ischemic cells fail to take up the isotope (thallium-201 or Cardiolite) and thus appear as cold spots on a scan. Thallium imaging should show normal distribution of the isotope throughout the left ventricle with no defects (cold spots).

What resting reveals

To distinguish normal from infarcted myocardial tissue, the practitioner may order an exercise thallium scan followed by a resting perfusion scan. A resting perfusion scan helps differentiate between an ischemic area and an infarcted or scarred area of the myocardium. Ischemic myocardium appears as a reversible defect (the cold spot disappears). Infarcted myocardium shows up as a nonreversible defect (the cold spot remains).

Thallium scanning

Also known as cold spot imaging, thallium scanning evaluates myocardial blood flow and myocardial cell status. This test helps determine areas of ischemic myocardium and infarcted tissue. It can also help evaluate coronary artery and ventricular function as well as pericardial effusion. Thallium imaging can also detect a myocardial infarction in its first few hours. (See Understanding thallium scanning.)

The test uses thallium-201, a radioactive isotope that emits gamma rays and closely resembles potassium. When injected I.V., the isotope enters healthy myocardial tissue rapidly but enters areas with poor blood flow and damaged cells slowly. A camera counts the gamma rays and displays an image. Areas with heavy isotope uptake appear light, whereas areas with poor uptake, known as “cold spots,” look dark. Cold spots represent areas of reduced myocardial perfusion.

NURSING CONSIDERATIONS

·

Tell the patient to avoid heavy meals, cigarette smoking, and strenuous activity for 24 hours before the test.

 

·

If your patient is scheduled for an exercise thallium scan, advise him to wear comfortable clothes or pajamas and snug-fitting shoes or slippers.

·

After the procedure, permit the patient to resume activities, as indicated.

Doppler ultrasonography

Doppler ultrasonography evaluates blood flow in the major blood vessels of the arms and legs and in the extracranial cerebrovascular system. A handheld transducer directs high-frequency sound waves to the artery or vein being tested.

The sound waves strike moving red blood cells and are reflected back to the transducer at frequencies that correspond to blood flow velocity through the vessel. The transducer then amplifies the sound waves to permit direct listening and graphic recording of blood flow. Measurement of systolic pressure helps detects the presence, location, and extent of peripheral arterial occlusive disease.

Pulse volume recorder testing may be performed along with Doppler ultrasonography to yield a quantitative recording of changes in blood volume or flow in an extremity or organ. (See Measuring the ankle-brachial index, pages 138 and 139.)

Normally, venous blood flow fluctuates with respiration, so observing changes in sound wave frequency during respiration helps detect venous occlusive disease. Compression maneuvers can also help detect occlusion of the veins as well as occlusion or stenosis of carotid arteries. Abnormal images and Doppler signals may indicate plaque, stenosis, occlusion, dissection, aneurysm, carotid body tumor, and arteritis.

NURSING CONSIDERATIONS

·

Explain the test to the patient, and tell him that it takes about 20 minutes.

·

Check with the vascular laboratory to determine whether special equipment will be used and whether special instructions are necessary.

·

Water-soluble conductive gel is applied to the tip of the transducer to provide coupling between the skin and the transducer.

Venography of the leg

Also known as ascending contrast phlebography, a venography is a radiographic examination of veins in the lower extremity that's commonly used to assess the condition of the deep leg veins after injection of a contrast medium.

MEASURING THE ANKLE-BRACHIAL INDEX

A Doppler ultrasound device can also be used to measure ankle-brachial index (ABI) to help identify peripheral vascular disease. To perform this test, follow these steps.

·

Explain the procedure to the patient.

·

Gather your materials.

·

Wash your hands.

·

Apply warm conductivity gel to the patient's arm where the brachial pulse has been palpated and then obtain the systolic reading.

c3-tt25

·

Locate the posterior tibial pulse and repeat the procedure, recording your reading.

     

c3-tt26

·

Locate the dorsalis pedis pulse and repeat the procedure.

     

·

Use the chart below to calculate the ABI. Document your findings.

c3-tt27

     

Calculating ABI

To calculate ABI, divide the higher systolic pressure obtained for each leg (dorsalis pedis or posterior tibial) by the higher brachial systolic pressure.

SAMPLE SYSTOLIC

READINGS (MM HG)

LEFT

RIGHT

Posterior tibial

128

96

Dorsalis pedis

130

90

Brachial

132

130

Calculations

130 ÷ 132 = 0.98

96 ÷ 132 = 0.73

 

·

Greater than 1.3: Unreliable and inconclusive; possibly false-high readings produced by calcified vessels (such as occurs in diabetes)

·

1.01 to 1.3: Correlates with patient history (especially in diabetes)

·

0.97 to 1: Normal

·

 

·

0.4 to 0.79: Moderate to severe ischemia

·

0.39 or less: Severe ischemia; danger of limb loss

This procedure isn't used for routine screening because it exposes the patient to relatively high doses of radiation and can cause such complications as phlebitis, local tissue damage and, occasionally, deep vein thrombosis (DVT). It's used in patients whose duplex ultrasound findings are unclear.

NURSING CONSIDERATIONS

·

Make sure the patient has signed an appropriate consent form.

·

Note and report allergies.

·

Check the patient's history for and report hypersensitivity to iodine, iodine-containing foods, or contrast media.

·

Reassure the patient that contrast media complications are rare, but tell him to report nausea, severe burning or itching, constriction in the throat, or dyspnea at once.

·

Discontinue anticoagulation therapy, as indicated.

·

Administer sedation indicated.

·

Instruct the patient to restrict food and to drink only clear liquids for 4 hours before the test.

·

Warn the patient that he might experience a burning sensation in the leg when the contrast medium is injected as well as some discomfort during the procedure.

·

If DVT is documented, initiate therapy (heparin infusion, bed rest, leg elevation or support) as indicated.