Figure 4.

Top panel of electrocardiogram (ECG) trace shows obvious atrioventricular (AV) dissociation (P waves are indicated with triangular symbols) during the occurrence of premature ventricular contraction and bidirectional ventricular tachycardia (BD-VT). Bottom panel shows ECG trace (top) with BD-VT and 2 right atrial electrocardiograms (RA1 and RA2). Note that atrial tachyarrhythmia was induced immediately after the burst atrial pacing. However, the BD-VT was not affected by the atrial burst pacing and the induction of atrial tachyarrhythmia, further indicating AV dissociation during BD-VT.