Detection of concealed left sided accessory atrioventricular pathway by P wave signal averaged electrocardiogram

Objectives. The purpose of this study was to examine whether P wave signal-averaged electrocardiogram (P-SAECG), which detects subtle changes in P wave, detects the concealed accessory atrioventricular pathway (AP). Background. It is difficult to differentiate atrioventricular reciprocating tachycardi (AVRT) due to the AP from atrioventricular nodal reentrant tachycardi (AVNRT) when the ventricular preexcitation is absent on 12-lead electrocardiograms. By electrophysiological studies, the anterograde conduction in the concealed AP is shown to be blocked near the AP-ventricular interface during sinus rhythm. Methods. P-SAECG during sinus rhythm was performed in 20 normal volunteers (control), 21 patients with AVRT due to the concealed AP, 19 with AVNRT, 22 with paroxysmal atrial fibrillation (PAF), and 7 with automatic atrial tachycardi (AT). The filtered P wave duration (FPD) and AR20 (power spectrum are ratio of 0–20 to 20–100 Hz) were measured and repeated in AVRT, AVNRT and AT groups at one week after catheter ablation. Results. The anterograde conduction in the concealed left-sided AP was confirmed in all cases by an electrophysiological study. The FPD in AVRT group was more prolonged than that in controls or AVNRT group. Although the FPD was similar between AVRT and PAF groups, AR20 differentiated between the two groups. Ablation of the concealed AP shortened FPD in AVRT group but that of the slow pathway or the atrial focus did not shorten in the AVNRT or AT groups, respectively. The changes in FPD after ablation were correlated with those in the duration of atrial activity by an electrophysiological study (r = 0.67). Conclusions. Our findings suggest that P-SAECG detects the concealed left-sided AP, providing clinical tool in noninvasively assessing atrial activation patterns