Atrial Entrainment During Posterior Fascicular Ventricular Tachycardia

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A 20‐year‐old gentleman underwent electrophysiology study for paroxysmal palpitation. The surface electrocardiogram during sinus rhythm did not show any preexcitation. Echocardiogram was normal. Basal intervals including atrio‐Hisian (AH) and Hisio‐ventricular (HV) intervals were 115 and 42 ms, respectively. Catheter manipulation induced regular tachycardia with right bundle branch block morphology, left superior axis, and ventriculo‐atrial (VA) dissociation. In view of no underlying structural heart disease, the possibility of posterior fascicular ventricular tachycardia (VT) was considered. Pacing from mid postero‐inferior left ventricular septum allowed entrainment with concealed fusion and similar post pacing interval as that of tachycardia cycle length.
Atrial pacing (Figs. 1 and 2) from right atrium was done during VT. The QRS morphology exhibited fusion and subsequent narrowing of QRS suggestive of entrainment of tachycardia circuit in the ventricle by atrial pacing. The subsequent VT has been reset because the interval between the last entrained QRS and VT was more than the VT cycle length. The interval between the last captured QRS and VT was prolonged with shortening of the pacing cycle length, presumably owing to decremental conduction within the reentry circuit.
Posterior fascicular VT utilizes the mechanism of reentry and it can be induced, entrained, and terminated by programmed ventricular or atrial stimulation. Entrainment by atrial pacing suggests intimate access to the circuit from the normal conduction system into the reentrant circuit whether the latter consists of reentry within the normal network or, in part, at least an accessory substrate related closely to the former.
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