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

We sought to evaluate the incidence and electrophysiological features of the local slow potential preceding the surface QRS complex (pre-QRS potential) which was detected more frequently at successful sites of catheter ablation of left parietal concealed accessory pathways, than at unsuccessful sites.