Atrial Entrainment During Posterior Fascicular Ventricular Tachycardia
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.