of study to collect history of patients with preexcitation syndrome (PS)-related adverse event (AE) and evaluate their risk factors. Classicaly male sex, multiple accessory pathways (AP) and at electrophysiological study (EPS), refractory period (RP)<250ms and shortest RR interval during atrial fibrillation (AF)<250ms are signs of risk of AE.

AE occurred in 83 among a population of 970 patients consecutively recruited for a PS (8.5%) (resuscitated sudden death (n=8), or documented AF conducted with a rapid rate over AP (>300 bpm), cause of syncope and requiring cardioversion (17) or drug (58). ECG, Holter monitoring and EPS in control state (CS) and after isoproterenol were performed.

Patients with AE were older than remaining patients (40±8.5 vs 33±17) (p 0.0002). Male gender did not differ significantly (71 vs 61%)(p 0.06). ECG in sinus rhythm was normal or near normal in 20 patients with AE (24%) more frequently than in patients without AE (9%)(p 0.0001). Intermittent PS was seen only in patients without AE. At EPS atrioventricular reentrant tachycardia (AVRT) was induced as frequently in patients with AE as in patients without AE (60% vs 53.5%)(0.22). All other electrophysiological data differ significantly (p 0.0001): maximal rate conducted over AP was more rapid in patients with AE (262±50 bpm vs 183±65 in CS, 302±39 vs 228.5±69 after isoproterenol). AP effective refractory period was shorter in patients with AE (232±34 vs 292±73 in CS, 197±29 vs 232±50ms after isoproterenol); AF was induced more frequently in patients with AE (72 vs 19.5%). Signs of malignancy at EPS were noted in all but 4 patients (sensitivity 95%).

If electrophysiological data evaluated in CS and after isoproterenol have high sensitivity (95%) to predict PS-related adverse event, the detection of PS can be difficult. In 20% of patients who presented with an adverse event, the diagnosis of PS was not made because ECG in sinus rhythm was normal.