Figure legends
Figure 1. (A) The surface and intracardiac electrograms during sinus rhythm. (B) Those during wide QRS complex tachycardia (WCT). Note that the QRS morphology during WCT is identical to those during SR. The numbers represent HH intervals.
Figure 2. Transient AH block and the subsequent VA perturbation without AA interval perturbation. The second QRS after AH block (asterisk) is the fusion QRS with the premature ventricular contraction. Note the gradual prolongation of AH leading to the fixed AH interval after AH block, suggestive of the transition from the antegrade fast to the slow pathway.