Color Atlas and Synopsis of Electrophysiology, 1st Ed.


Venkata Krishna Puppala, MD, and David G. Benditt, MD


A 67-year-old man came to the Syncope/Electrophysiology Clinic complaining of experiencing periodic “dizzy spells” and, more recently, two frank collapse events. The dizzy spells have become more frequent over the past year, and during these episodes he feels that his vision diminishes briefly then recovers. The two abrupt transient loss of consciousness spells were more severe. The first occurred as he was getting ready for bed, and he found himself on the bedroom floor. There were no warning symptoms. His wife indicated that his color seemed flushed, and his eyelids remained open. The second occurred while pushing a shopping cart but not otherwise exerting himself. There was no warning as far as he could recall; he held on to the cart in order to avoid injury as he collapsed. He recovered promptly and was not injured.

The patient’s only cardiac history is hyperlipidemia for which he takes simvastatin. A recent echocardiogram showed modest left atrial enlargement (43 mm), mild concentric left ventricular hypertrophy (septal and free wall thickness approximately 12 mm), and a normal left ventricular ejection fraction (55%-60%). His 12-lead ECG was normal.

Given the infrequent nature of the frank syncope events in a patient without major structural heart disease (ie, presumably a low risk of a life-threatening cardiac cause for syncope) an ambulatory ECG monitoring strategy was chosen for subsequent evaluation; specifically, an implantable loop recorder (ILR) was selected since it would permit long-term monitoring to capture infrequent evens (Figure 45-1). Within a few days he reported an episode of his usual dizziness, accompanied by extreme fatigue and weakness. His ILR recording revealed sinus rhythm with ventricular bigeminy resulting in a slow effective heart rate (Figure 45-2). Given his weakness with this rhythm, the possibility was entertained that the bigeminy could be the basis for his dizziness and syncope, but it was decided to wait longer and continue monitoring.


FIGURE 45-1 Picture of a typical implantable loop recorder. Note the size relative to the finger. (Image used with permission of Medtronic Inc., Minneapolis, Minnesota.)


FIGURE 45-2 Ventricular bigeminy associated with “dizzy” spell, presumably due to a slow net heart rate.

Approximately 6 weeks later, the patient slumped to the floor while sweeping out his garage. His wife called 911, and he was brought to the emergency department. His ILR was interrogated, and a diagnosis of symptomatic bradycardia was established (Figure 45-3). Based on this finding a pacemaker was indicated. During the subsequent year he has not suffered any further syncope episodes. However, ablation of ventricular ectopy has been scheduled given his persistent ventricular bigeminy and “dizzy” spells.


FIGURE 45-3 Prolonged asystolic pause recorded by ILR in conjunction with the patient’s abrupt collapse.


Syncope (“faint”) is a brief, self-limited period (usually less than 1-2 minutes) in which loss of consciousness occurs a result of transient cerebral hypoperfusion. There are many possible causes. The percentage of patients who report having experienced a faint varies from 15% to 25% in Western countries.1,2 Syncope accounts for 1% of all visits to emergency departments or urgent care clinics in Europe and around 1% to 6% of such visits in the United States.1-3


Vasovagal and orthostatic faints are the most common forms of syncope across all age groups.1,4-6 In younger patients without any structural heart disease, neurally mediated reflex faints, particularly vasovagal syncope or situational faints (eg, postmicturition syncope, cough syncope), account for the vast majority. In older patients, carotid sinus syndrome (CSS) becomes of increasing importance and has been reported to account for up to 20% of syncope in this group.1,4 Older patients are also more likely to experience orthostatic syncope.4

Cardiac causes of syncope include structural heart disease (ie, coronary artery disease, valvular disease, cardiomyopathies, consequences of hypertension) and arrhythmias. Increased mortality risk is a concern in these patients1,5; however, the primary mortality “driver” is the severity of the underlying heart disease rather than the syncope itself.1 In the absence of overt structural disease, the possibility of a so-called channelopathy (eg, long QT syndrome, Brugada syndrome, catecholaminergic paroxysmal VT) should not be overlooked.1 In addition, occasionally premature coronary artery disease may trigger an arrhythmia in individuals who are seemingly healthy.


The urgency of establishing the basis of syncope is determined by assessment of the patient’s short-term and long-term potential morbidity and mortality risk. This “risk assessment” step has received considerable attention recently.1-6,11 Its importance relates in part to potential for sudden unexpected death in such patients, but also (and perhaps more commonly) to susceptibility for syncope to recur in affected individuals and result in falls with injury and economic and life-style disruption. Table 45-1 provides a list of clinical findings (derived from multiple reports) that trigger concern regarding high risk of early (<1 month) syncope recurrence.

TABLE 45-1 Clinical Observations Suggesting Increased Risk in Syncope/Collapse Patients


Longer-term risk of syncope recurrence (ie, <1 year) is more difficult to predict. However, a few studies have attempted to address this issue.1,6 Table 45-1 summarizes a number of clinical observations that should raise concern regarding increased risk of syncope recurrence over the next year.


Figure 45-4 summarizes a basic strategy for the initial clinical evaluation and disposition of syncope/collapse patients. The initial evaluation requires a careful medical history (including accounts from witnesses) followed by risk assessment or risk stratification. The availability of a syncope clini or syncope management unit is of value in order to enhance efficiency of patient care by avoiding unnecessary hospitalizations and diminishing the number of “diagnostic” tests being ordered, while increasing diagnostic yield.


FIGURE 45-4 Management strategy for patients presenting to emergency departments or clinics with transient loss of consciousness and presumed syncope.

A preprepared history form may facilitate the recording of a complete story. The provider should try to obtain the answers for the following key questions as part of the history taking:

• Is loss of consciousness attributable to true syncope versus other causes of real or seemingly real loss of consciousness, including accidental falls?

• Is heart disease present?

• Are there important clinical features in the history that suggest the diagnosis? (eg, premonitory symptoms in vasovagal fainters)

• What were the circumstances of the collapse? (eg, emotional upset, fear, pain, during or after exertion, after cough, while supine or recumbent, after having recently stood up from a seated or supine position)

In regard to physical findings, most “presumed syncope” patients have fully recovered by the time they are first seen by a medical practitioner. Consequently, the relation between physical finding abnormalities (if any) and the cause of syncope is inferential in most cases. However, physical findings that may assist in uncovering a basis for syncope include marked drop in blood pressure when arising (ie, orthostatic blood pressure changes), important cardiac murmurs or bruits, evidence of heart failure or left ventricular disease, and an abnormal response to carotid sinus massage.


Pooled data from population-based studies indicate that the history and physical examination can identify a potential cause of syncope in approximately 50% of the patients.1 An ECG should be obtained in all patients presenting with syncope. The ECG has been noted to be helpful in diagnosing a cardiac cause of syncope in approximately 6% of all patients with syncope and 50% of patients with a cardiac cause of syncope. On the other hand, routine blood tests rarely yield diagnostically useful information, and any such tests should be selected based on suspicion arising during the history taking. Very rarely such tests may yield other nonsyncope diagnoses such as hypoglycemia and intoxication. Similarly, head imaging (in the absence of head injury) and carotid Doppler imaging are to be avoided in most cases as they are highly unlikely to explain the faint.


Neurally Mediated Syncope

As noted earlier, “reflex” faints, and particularly vasovagal syncope (VVS), are the most common causes of syncope when one considers all age groups. VVS alone is reported to occur in 10% to 20% of the general population.

In the case of VVS and the closely related situational syncope (eg, syncope associated with swallowing, cough, and postmicturition), a good medical history is generally sufficient to establish the diagnosis.1Treatment of these forms of reflex syncope mainly consists of avoiding or ameliorating triggers when possible (ie, for situational faints), along with education and increased salt and volume intake if medically safe. Pharmacologic treatments have been proposed, but none have showed convincing benefit in placebo-controlled trials with the exception of midodrine.12-17 The role of cardiac pacing for vasovagal syncope remains controversial. ISSUE 2 and the more recent ISSUE 3 trials suggest that cardiac pacing may be beneficial in older patients with a documented prolonged spontaneous asystole.18,19

Carotid sinus syndrome (CSS) occurs most often in older males. The conventional criteria for a diagnostic finding with carotid sinus massage (CSM) is a pause ≥3 sec with symptoms.1 However, such a finding is only likely to occur if the CSM test is conducted with the patient in an upright posture, and even then the test has been criticized for not being sufficiently specific.20 A recent consensus opinion suggests that the CSS diagnostic bar should be set higher20; specifically, CSM with a pause ≥6 sec with reproduction of syncope or near-syncope is almost certainly a more specific manner in which to establish a CSS diagnosis. Cardiac pacing is generally effective, although vasoconstrictors such as midodrine may also be needed if a prominent vasodepressor response is also present.

Orthostatic Syncope

Orthostatic syncope is diagnosed when there is documentation of posturally induced hypotension associated with syncope or near-syncope. Two forms are recognized: the “immediate” form that occurs promptly after movement to the upright posture and then disappears quickly, and the more troublesome “delayed” form, which consists of a drop in systolic blood pressure by ≥20 mm Hg within 3 to 5 minutes (sometimes longer) after assuming a standing posture.

Orthostatic syncope can be the result of either nonneurogenic reversible causes (eg, volume depletion, effect of medications) or primary neurologic conditions like Parkinson’s disease or pure autonomic failure. When physical maneuvers and salt/volume repletion alone are not sufficient to suppress orthostatic symptoms, pharmacological interventions may be justified. Fludrocortisone and midodrine are probably the most commonly used drugs.15,16

Cardiac Arrhythmias

Syncope can be caused by both brady- and tachyarrhythmias. Bradyarrhythmias may be due to sinus node dysfunction (eg, severe sinoatrial bradycardia, sinus pauses, or occasionally asystolic pauses following termination of atrial tachyarrhythmias), chronic or paroxysmal atrioventricular (AV) block, or third-degree AV block. The severity of the bradycardia must be sufficient to account for abrupt cerebral hypoperfusion. In situations where the diagnosis is not certain, further testing with ambulatory event monitoring, electrophysiological assessment of AV conduction, and sometimes exercise testing to look for rate-dependent AV block. Pacemaker therapy is usually appropriate and effective in such cases. In our patient, despite absence of overt heart disease, intermittent sinus arrest was determined to be the cause of syncope, whereas his ventricular bigeminy was a less serious issue, but the apparent cause of his “dizzy” spells.

Tachyarrhythmias, of either supraventricular or ventricular origin, can cause syncope. Depending on the arrhythmia at fault, treatment options may include any combination of antiarrhythmic drugs (including β-blockers and calcium channel blockers) and radiofrequency catheter ablation (RFA). RFA is the treatment of choice for certain idiopathic monomorphic VTs (eg, right and left ventricular outflow tract VTs and the so-called fascicular VTs). Other, less common but important arrhythmic causes of syncope include torsades de pointes associated with long-QT syndromes (including drug-induced forms) or Brugada syndrome.

Structural Cardiac and Cardiopulmonary Causes of Syncope

In patients with structural cardiac or cardiopulmonary disease, syncope may be due to direct result of the structural disturbance or as a consequence of a neural-reflex disturbance triggered by the condition, or due to an arrhythmia (bradycardia or tachycardia). Important causes in this group include acute myocardial infarction, severe aortic stenosis, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy.

Cerebrovascular Causes of Syncope

In general, cerebrovascular diseases are seldom the cause of true syncope; extensive neurologic testing such as head imaging or electroencephalography are rarely of value in the initial assessment of patients presenting with syncope. Head imaging may be occasionally necessary if there is a concern that the patient may have sustained an intracranial injury as a consequence of their collapse.

Conditions That Mimic Syncope

Certain conditions may cause a real or apparent loss of consciousness that might appear to be syncope, but is not true syncope.17 Examples of such situations include seizures, pseudosyncope (pseudoseizures), concussions, or intoxication. Cataplexy and certain rare types of akinetic or minimally kinetic seizures may also be considered here.


Syncope is a syndrome that is a particularly frequent cause for emergency department and urgent care clinic visits. The physician’s key tasks are to establish a confident causal diagnosis, assess prognostic implications, and then provide appropriate advice to prevent recurrences. To achieve these goals, it is important to develop an organized approach to assessment of the syncope patient. The initial patient evaluation, particularly a detailed medical history, is the key to identifying the most likely diagnosis and ascertaining the short-term mortality/morbidity risk. The latter allows one to determine whether urgent hospitalization is needed or whether the patient can be safely (and more economically) be evaluated as an outpatient. Based on findings from this initial step, subsequent carefully selected diagnostic tests can be chosen to confirm the diagnostic clinical suspicion, and thereby initiate effective preventive therapy.


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