Yoshinori Kobayashi, MD; Yasushi Miyauchi, MD; Naomi Kawaguchi, MD; Kazuko Ohmura, MD; Hirokazu Saitoh, MD; Takeshi Ino, MD; Hirotsugu Atarashi, MD; Takao Katoh, MD; Hiroshi Kishida, MD; Hirokazu Hayakawa, MD

Abstract
A case of Wolff-Parkinson-White (WPW) syndrome with several interesting electrophysiologic findings is presented. Although manifest preexcitation had not been documented in clinical routine check-ups for the 2 years before the ablation session, an intermittent preexcitation emerged after an initial unsuccessful radiofre-quency current delivery directed at the subvalvular mitral annulus 1cm distal from the subsequent successful ablation site. During intermittent manifestation of preexcitation, the following observations were made: (1) during manifest preexcitation, a possible Kent potential was recorded at the successful ablation site; (2) during non-preexcited impulse propagation, a local slow potential preceding the QRS complex (pre-QRS potential) was clearly observed at the same site; (3) the pre-QRS potential disappeared during orthodromic atrioventricular reci-procating tachycardia, spontaneous atrial premature contraction and after the subsequent successful ablation; and (4) when the pre-QRS potential was obvious, a small change in QRS morphology of the body-surface ECG was appreciable, compared with that during beats of negative pre-QRS potential. A comparable preceding compo-nent was also detected in a signal-averaged ECG. It is considered that the pre-QRS potential might be related to the anterograde concealed conduction through the accessory pathway.
(Jpn Circ J 1998; 62: 760- 764)

Key Words: Anterograde concealed conduction; Local pre-QRS potential; Radiofrequency catheter ablation; Signal-averaged ECG; Wolff-Parkinson-White syndrome

Mailing address: Yoshinori Kobayashi, MD, The First Department of Internal Medicine, Nippon Medical School, 1-1-5, Sendagi, Bunkyo-ku, Tokyo 113, Japan