Among patients who endorse a history of palpitations, the sensation of rapid and regular pulsations in the neck points very strongly toward an AV-nodal re-entrant tachycardia, because the carotid pulse and cannon A wave arrive simultaneously in the neck.5 Postictal confusion and focal neurologic exam findings suggest a neurologic rather than syncopal cause, although there are exceptions, and the relationship between seizure and impaired myocardial perfusion is complex.
One factor shown to be significantly associated with a cardiac cause for episodic syncope is family history of sudden cardiac death.4
Physical exam: A thorough general and neurologic exam is critical in evaluation of a first syncopal episode. Supine and standing blood pressure and heart rate should be measured, waiting at least one minute (and by some protocols up to three minutes) after the patient stands up to record standing vitals. Measurement of sitting vitals is not necessary. Neither postural hypotension nor tachycardia are sensitive for hypovolemia in normal volunteers, but a 30-point increase in heart rate is more than 99% specific; a 20-point drop in systolic blood pressure (SBP) is less so.5 A difference of more than 20 mmHg between systolic arm pressures in an individual with chest pain suggests aortic dissection.
Other findings useful in diagnosis of syncope include signs of aortic stenosis, pulmonary hypertension, and myxoma. Absent aortic component of S2, a late-peaking or prolonged murmur, sustained apical impulse, and delayed carotid upstroke (“pulsus tardus”) strongly support the presence of severe aortic stenosis. Absence of a palpable pulmonic component of S2 argues strongly against significant pulmonary hypertension.
There are few physical exam findings reliably seen in pulmonary embolism, but the presence of tachycardia is reliably seen about 80% of the time.4 Although atrial myxoma is associated with a characteristic “tumor plop” heard in early diastole, the finding is not common.5
Diagnostic studies: In a recent observational study of more than 2,000 adults older than 65 hospitalized after a syncopal episode, cardiac enzymes, electroencephalography, CT scan of the head, and carotid ultrasonography determined the etiology of syncope in less than 1% of cases. Inpatient monitoring on telemetry was helpful about 5% of the time. On the other hand, postural vital signs contributed to the diagnosis more than 20% of the time, at a fraction of the cost of these other diagnostics (see Table 2, above).6
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The role of transthoracic echocardiogram (echo) is more controversial. It does seem clear, however, that echo is more likely to be diagnostic in adults older than 60, in the presence of a heart murmur on physical exam or with an abnormal ECG.7 Although it demonstrated an arrhythmia that determined the etiology of syncope in only 3% of cases in this study, ECG is still routinely recommended; it is relatively inexpensive, risk-free, and can reveal abnormalities, including bundle-branch block, prior MI, and nonsustained ventricular tachycardia, which may be associated with cardiovascular comorbidities.4
Although the diagnostic tests above are of limited utility in uncovering the cause of syncopal episodes, they may be helpful when history or physical examination suggests a specific cause. For example, in individuals presenting with syncope who have lateralizing neurologic signs or symptoms or carotid bruits, carotid ultrasound is an appropriate diagnostic tool. In a retrospective analysis of 140 older adults who underwent carotid ultrasonography as part of a syncope evaluation, carotid lesions were identified in just 2% of subjects.8 These lesions were not thought to have been the primary etiology of syncope but did prompt additional evaluation or intervention.
Among older individuals or individuals with known heart disease, longer-term cardiac monitoring might be appropriate. The method of cardiac monitoring should be guided by the frequency of episodes. For events occurring daily, Holter monitoring is appropriate. For events occurring at least monthly, an event monitor is appropriate.