Atlas of pathophysiology, 2 Edition

Part II - Disorders

Cardiovascular disorders

Cardiac Tamponade

Cardiac tamponade is a rapid, unchecked rise in pressure in the pericardial sac that compresses the heart, impairs diastolic filling, and limits cardiac output. The rise in pressure usually results from blood or fluid accumulation in the pericardial sac (pericardial effusion). Even a small amount of fluid (50 to 100 ml) can cause a serious tamponade if it accumulates rapidly.

Causes

·   Idiopathic

·   Effusion (due to cancer, bacterial infections, tuberculosis or, rarely, acute rheumatic fever)

·   Traumatic or nontraumatic hemorrhage

·   Viral or postirradiation pericarditis

·   Chronic renal failure requiring dialysis

·   Drug reaction (procainamide, hydralazine, minoxidil, isoniazid, penicillin, or daunorubicin)

·   Heparin- or warfarin-induced tamponade

·   Connective tissue disorders

·   Postcardiac surgery

·   Acute myocardial infarction

Pathophysiology

In cardiac tamponade, the progressive accumulation of fluid in the pericardial sac causes compression of the heart chambers. This compression obstructs filling of the ventricles and reduces the amount of blood that can be pumped out of the heart with each contraction.

Each time the ventricles contract, more fluid accumulates in the pericardial sac. This further limits the amount of blood that can fill the ventricular chambers, especially the left ventricle, during the next cardiac cycle.

The amount of fluid necessary to cause cardiac tamponade varies greatly; it may be as little as 50 to 100 ml when the fluid accumulates rapidly or more than 2,000 ml if the fluid accumulates slowly and the pericardium stretches to adapt. Prognosis is inversely proportional to the amount of fluid accumulated.

Signs and symptoms

·   Elevated central venous pressure (CVP) with jugular vein distention

·   Muffled heart sounds

·   Pulsus paradoxus

·   Diaphoresis and cool, clammy skin

·   Anxiety, restlessness, syncope

·   Cyanosis

·   Weak, rapid pulse

·   Cough, dyspnea, orthopnea, tachypnea

Clinical Tip

Cardiac tamponade has three classic features, known as Beck's triad, that include:

·   elevated CVP with jugular vein distention

·   muffled heart sounds

·   pulsus paradoxus.

Diagnostic test results

·   Chest X-rays show a slightly widened mediastinum and possible cardiomegaly. The cardiac silhouette may have a goblet-shaped appearance.

·   Electrocardiography (ECG) detects a low-amplitude QRS complex and electrical alternans, an alternating beat-to-beat change in amplitude of the P wave, QRS complex, and T wave. Generalized ST-segment elevation is noted in all leads.

·   Pulmonary artery catheterization detects increased right atrial pressure, right ventricular diastolic pressure, and CVP.

·   Echocardiography reveals pericardial effusion with signs of right ventricular and atrial compression.

Treatment

·   Supplemental oxygen

·   Continuous ECG and hemodynamic monitoring

·   Pericardiocentesis

·   Pericardectomy

·   Resection of a portion or all of the pericardium

·   Trial volume loading with crystalloids

·   Inotropic drugs, such as isoproterenol or dopamine

·   Posttraumatic injury: blood transfusion, thoracotomy to drain reaccumulating fluid, or repair of bleeding sites may be needed

·   Heparin-induced tamponade: heparin antagonist protamine sulfate to stop bleeding

·   Warfarin-induced tamponade: vitamin K to stop bleeding

P.43

CARDIAC TAMPONADE

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