[Syncope in supraventricular tachycardia. Incidence, pathomechanism and consequences].

Syncope occurs in up to 20% of patients with supraventricular tachycardias and is suggestive of rapid and dangerous arrhythmias. Incidence, pathomechanism and consequences of syncope in supraventricular tachycardia are reviewed in this presentation. Frequent symptoms in supraventricular tachycardias are palpitations, dizziness or dyspnea. Syncope is more uncommon, however, if a sensation of rapid heart beat precedes a syncope, a causal relationship between arrhythmia and syncope has to be considered. When the surface ECG shows no abnormalities, Holter monitoring or exercise testing usually fail to record a suspected tachycardia, therefore, electrophysiologic study should be performed to verify the underlying arrhythmia. In patients with unexplained syncope supraventricular arrhythmias can be established in up to 15% of patients. However, interpretation of electrophysiologic results has to be performed carefully because functional abnormalities like dual AV nodal pathways can be found in up to 10% of asymptomatic patients. The prognostic value of syncope as a marker for rapid tachycardia or sudden cardiac death is still in discussion. Syncope in patients with Wolff-Parkinson-White syndrome may help to identify patients at risk for ventricular fibrillation due to rapid conduction over an atrioventricular accessory pathway during atrial fibrillation. Syncope in young patients (< 25 years) with Wolff-Parkinson-White syndrome was found to be associated with a short anterograde refractory period (< 220 ms) of the pathway. However, most of the studies were performed retrospectively in selected patients referred to the centers because of severe symptoms, therefore the predictive value of syncope in unselected patients with supraventricular tachycardia remains uncertain.(ABSTRACT TRUNCATED AT 250 WORDS)