Multiple wide QRS tachycardias in the same individual with ischemic cardiomyopathy

A 67 ?year?old diabetic man with ischemic cardiomyopathy presented with a recurrent defibrillator shock. His electrocardiograms showed both narrow (NCT) Figure 1A) and wide complex tachycardias (WCT; Figure 1B). He experienced an anterior myocardial infarction (MI) 11 years earlier that caused the left ventricular ejection fraction to decrease to 25%, and subsequently, a coronary artery bypass surgery was performed and, then implantable cardioverter?defibrillator was implanted for primary prophylaxis 2 years ago. The patient underwent to electrophysiological study for his WCT with a prediagnosis of incessant ventricular tachycardia (VT). In the first stage, the His signals were poor; however, we noticed that the premature ventricular complexes (PVC) reset the subsequent cycle lengths (Figure 2). Since the WCT was right bundle branch block (RBBB) morphology; we applied premature atrial complexes (PAC) with (Figure 3A) and without (Figure3B) septal refractory. Interestingly, we noticed the change in the QRS morphology (Figure 4) and ventriculoatrial (V?A; Figure 5) during ongoing WCT. What are the mechanism of the different QRS morphology and ventriculoatrial (V?A) responses of this tachycardia?