Local slow potential preceding the surface QRS complex detected at the subvalvular mitral annulus in patients with a left-sided concealed accessory pathway - Incidence, electrophysiological characteristics and the possible mechanism, with demonstration of anterograde concealed conduction through the pathway

Aim We sought to evaluate the incidence and electrophysiological features o f the local slow potential preceding the surface QRS complex (pre-QRS poten tial) which was detected more frequently at successful sites of catheter ab lation of left parietal concealed accessory pathways, than at unsuccessful sites. Methods and Results Thirty eight consecutive patients with a single left si ded concealed accessory pathway underwent radiofrequency catheter ablation exclusively from the subvalvular mitral annulus. The local bipolar electrog rams during sinus rhythm from the target sites were carefully analysed and the incidence of pre-QRS potentials was compared between successful and uns uccessful ablation sites. All ablation sessions attained a successful outco me with a total of 84 radiofrequency current applications (38 at successful sites, 46 at unsuccessful sites). The incidence of pre-QRS potentials (pre ceding by 10 ms or more) was 12/38 at successful sites (32%) and 1/46 at un successful sites (2%) (P < 0.001). The QV interval, defined as the interval between the upstroke of the QRS complex and the ventricular electrogram, i ncluding the pre-QRS potential, was -5.6 +/- 9.1 ms at successful sites, wh ile it was 1.2 +/- 6.1 ms at unsuccessful sites (P < 0.001). The pre-QRS po tential disappeared during atrioventricular reciprocating tachycardia and r ight ventricular pacing, and was eliminated by successful ablation. Conclusions Detection of the pre-QRS potential was clinically relevant and could be distinguished from artifact. This potential may be caused by anter ograde concealed conduction through the accessory pathways. (Eur Heart J 19 99; 20: 1818-1825) (C) 1999 The European Society of Cardiology.