An intriguing case of regular RR and QRS alternans during idiopathic left posterior fascicle ventricular tachycardia.

This study represents a case of idiopathic left posterior fascicle ventricular tachycardia (LPF-VT), which is intriguing due to regular alternation of short-long RR intervals and QRS morphology. Transthoracic echocardiogram analysis did not detect any structural heart disease. A baseline electrophysiological study was performed. Intracardiac recording during tachycardia showed V-A dissociation, confirming the final diagnosis of idiopathic LPF-VT. No regularity in the monomorphic VT was recorded. Previous relevant studies suggested that a single focus with two exits in distal branches of the left posterior fascicle or two different foci localized in the Purkinje-myocardial network of the left posterior fascicle can clarify the mechanisms. Our team proposed an additional explanation that combines the physiological refractory period with the Ashman phenomenon in individual reentrant LPF-VT circuit.