Changes in the Reentrant Pathway in Verapamil-Sensitive Fascicular Reentrant Ventricular Tachycardia During Ablation.

The sequence of changes in the QRS morphology and the accompanying cycle lengths of the tachycardia confirm that the reentrant circuit involves the left ventricular myocardium as well as the His Purkinje system as part of the reentrant circuit. The reentrant propagation likely goes from local left ventricular myocardium into a slowly conducting, verapamil-sensitive tissue, which then connects into the inferior fascicle. This case demonstrates that fascicular reentrant tachycardias can generate different QRS morphologies depending on the path of breakout into the myocardium.