SYNCOPE RESULTING FROM SUPRAVENTRICULAR T ACHYCARDIAS

Syncope occurs in up to 20% of patients with supraventricular tachycar dias and is suggestive of rapid and dangerous arrhythmias. Incidence, pathomechanism and consequences of syncope in supraventricular tachyca rdia are reviewed in this presentation. Frequent symptoms in supravent ricular tachycardias are palpitations, dizziness or dyspnea. Syncope i s 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 mo nitoring or exercise testing usually fail to record a suspected tachyc ardia, therefore. electrophysiologic study should be performed to veri fy the underlying arrhythmia. In patients with unexplained syncope sup raventricular arrhythmias can be established in up to 15% of patients. However, interpretation of electrophysiologic results has to be perfo rmed carefully because functional abnormalities like dual AV nodal pat hways can be found in up to 10% of asymptomatic patients. The prognost ic value of syncope as a marker for rapid tachycardia or sudden cardia c death is still in discussion. Syncope in patients with Wolff-Parkins on-White syndrome may help to identify patients at risk for ventricula r fibrillation due to rapid conduction over an atrioventricular access ory pathway during atrial fibrillation. Syncope in young patients (< 2 5 years) with Wolff-Parkinson-Whit, syndrome was un 0 be associated wi th a short anterograde refractory period (< 220 ms) of the pathway. Ho wever, 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 supravent ricular tachycardia remains uncertain. Tachycardia related symptoms li ke dizziness or syncope are due to hypotension depending on tachycardi a rate and mechanism. cardiac disease, posture and autonomic reflexes. Syncope was demonstrated to be a marker of rapid tachycardia during a trial fibrillation in young patients (< 25 years) with Wolff-Parkinson -White syndrome, however, did not correlate with the rate of reentrant tachycardias. In contrast syncope during reentrant tachycardia was as sociated with abnormal vasomotor response during tilt-testing. Sympath etic stimulation during tachycardia and upright posture may result in marked hypotension and syncope when vasomotor reflex mechanisms are in adequate. In patients with syncope and supraventricular tachycardia el ectrophysiologic study should be performed to further elucidate the me chanism. In the majority of patients curative treatment with radiofreq uency ablation of the accessory pathway or a slow AV nodal pathway may be performed during the same procedure.