Interesting case of narrow QRS tachycardia. What is the mechanism?

A 67‐year‐old female presented with history of recurrent palpitations. During one of the episodes of palpitation, a narrow QRS tachycardia was recorded and it was reported to be terminated with intravenous adenosine. The 12‐lead electrocardiogram (ECG) showed no manifest ventricular preexcitation. ECG was within normal limits. The patient underwent an electrophysiology study after informed consent. She was taking calcium channel blockers and that was stopped five half‐lives prior to the procedure. As catheters were being placed, a narrow QRS tachycardia got induced. During the study, there was development of right bundle branch block during the tachycardia. What is the mechanism of the tachycardia?     

Unchanged QRS morphology with atrial pacing in a case of WPW syndrome: What is the mechanism?

We present the case of a 55‐year‐old female who presented for a short episode of palpitation and an electrocardiogram consistent with Wolff‐Parkinson‐White syndrome. She underwent an electrophysiological study showing that during incremental atrial pacing and extrastimulation the stimulus to QRS and QRS morphology stayed constant while the His to ventricular (HV) interval shortened. What can be the explanation for the constant QRS morphology, despite shortening HV during atrial pacing?     

Clinical worsening due to inappropriate automatic mode switch during biventricular pacing: What is the mechanism?

We describe a case of a 65-year-old gentleman with nonischemic cardiomyopathy and left bundle branch block who underwent cardiac resynchronization therapy device. After becoming a responder initially, he experienced significant clinical worsening on follow-up. Device interrogation revealed several long episodes of inappropriate automatic mode switch (AMS) entry due to far-field R wave oversensing resulting in loss of atrioventricular synchrony. Moreover, pacing in VVI mode with consistent VA conduction taking place during the AMS episodes was also found to be detrimental, which helped in sustaining the episodes and produced pacemaker syndrome like phenomenon. Attempts made to resolve the issue by prolonging the post-ventricular atrial blanking period was unsuccessful, hence we adjusted the atrial channel sensitivity to troubleshoot the problem.