SYNCOPE



Syncope refers to sudden transient loss of con­sciousness, usually due to transient cerebral hypoperfusion. Presyncope is described as a light­headed spell that, if more prolonged, would cause loss of consciousness. Both may occur in the same patient and have similar etiologies. The causes of syncope are summarized in.

Cardiac syncope is due either to lesions that ob­struct outflow of blood from the heart or to ar­rhythmias. In patients with severe aortic stenosis or other causes of obstructive syncope, when the systemic vascular resistance decreases upon exercise, the heart is unable to augment cardiac output sufficiently to maintain perfusion and syncope results. Both tachyarrhythmias and bradyarrhythmias that result in cerebral hypo­perfusion can cause cardiac syncope. The hyper­sensitive carotid sinus syndrome, described above, is a well-recognized cause of syncope.

The history and physical examination are val­uable in excluding many causes of syncope . Even though the electrocardiogram may not reveal the actual arrhythmia causing syncope, electrocardiographic clues (for example, the pres­ence of simple or complex ventricular ectopy, ev­idence of a previous myocardial infarction, or the delta wave of the Wolff-Parkinson-White syn­drome) may suggest potential arrhythmic causes. Prolonged electrocardiographic (Holter) record­ing may be the cornerstone of diagnosis in ar­rhythmic syncope. On many occasions, more than 24 hours of recording are required to detect the responsible arrhythmia. Exercise testing is also valuable in some patients whose arrhythmias are exercise-induced. Patients with obstructive syn­cope such as aortic stenosis should not undergo exercise testing. In selected patients invasive elec­trophysiological studies may be useful to delin­eate the etiology of the syncope.