Syncope (Fainting)

It is important to ascertain whether syncopal spells occur only when patients are standing or sitting or whether they also occur when the individual is lying down. An orthostatic mechanism suggests benign spells if the patient has no demonstrable heart disease. Likewise, syncope precipitated by straining may suggest a benign mechanism in persons without heart disease.

A history of syncope occurring during exercise or while lying down demands attention. In some persons, exercise may provoke atrial or ventricular arrhythmias. Rarely, obstructive mechanisms such as familial heart muscle disease (hypertrophic cardiomyopathy) and narrowing of the aortic valve (aortic valve stenosis) may limit cardiac output during exercise. Sometimes, reflex cardiac slowing immediately after abrupt termination of exercise can trigger a benign syncope. Syncope while lying down is highly suggestive of a pathologic cause.

Drugs taken by patients experiencing syncope should be carefully reviewed. Among the drugs that may precipitate syncope are agents commonly prescribed to treat high blood pressure, such as ACE inhibitors, calcium channel blockers, beta blockers, and alpha blockers. Paradoxically, medications used to treat arrhythmias may as a side effect provoke arrhythmias and syncope. Some drugs prescribed by psychiatrists may both lower arterial pressure and/or induce arrhythmias. "Recreational" drugs such as amphetamines and cocaine may trigger arrhythmias and syncope. Excessive treatment with diuretics may unduly decrease blood volume and invite syncopal spells.

Depending upon the historical features of the syncopal episode, one or both of two tests may be performed. Tilt table testing is useful to assess the possible contribution of venous pooling or orthostatic mechanisms. An electrophysiology study addresses arrhythmias as mechanisms for syncope. The recognition of ventricular tachyarrhythmias as a cause of syncope is of paramount importance, because such syncopes are associated with a high risk of sudden cardiac death; syncope due to ventricular tachyarrhythmias might be called "spontaneous recovery from sudden cardiac death". Tachyarrhythmias are usually easy to detect and characterize during electrophysiology studies. Bradyarrhythmias, including sinus node dysfunction and AV block, can be very difficult to detect or reproduce during electrophysiology studies. If patients experience warning symptoms such as dizziness or palpitations, they may be given an ECG event recorder to ascertain whether syncopal spells are associated with arrhythmias.