A Tachycardia classified as Supraventricular by a Cardiac Resynchronization Therapy‐Defibrillator Device. What is the Mechanism?

Figure 1. Programmed tachycardia parameters in the Epic II+ HF device. tachycardia (VT), baseline left bundle branch block, and New York Heart Association class III heart failure. The programmed parameters were as follows: base rate 50/min, maximum tracking rate 125/min, sensed/paced atrioventricular (AV) delays 140/190 ms, rate-responsive AV delay— medium, and biventricular pacing with left ventricular first at 35 ms. The thresholds of all three leads were adequate and the programmed output had enough safety margin. The measured P and R waves were >3 mV and >12 mV, respectively. The special sensing parameters for atrial lead were automatic sensitivity with maximum 0.2 mV, decay delay 0 ms, and threshold start of 50% and for the ventricular lead were 0.3 mV, 60 ms, and 62.5%, respectively. The programmed tachycardia parameters were as seen in Figure 1. Stored electrogram (EGM) of an asymptomatic episode diagnosed