Abstract 18446: Reciprocating Bigeminy: A Possible Mechanism of Bidirectional Ventricular Tachycardia
Bidirectional ventricular tachycardia (BVT), characterized by alternating electrocardiographic QRS axis on alternate beats, is a rare but intriguing arrhythmia associated with digitalis toxicity, familial catecholaminergic polymorphic ventricular tachycardia (CPVT) and Anderson-Tawil long QT syndrome. In these conditions, cardiac myocytes are predisposed to delayed afterdepolarizations (DADs) and triggered activity. Evidence from human studies and optical mapping experiments in a genetic CVPT mouse model attribute BVT to alternating ectopic foci originating from the distal His-Purkinje system in the left and/or right ventricles, respectively. Here we propose a simple ”ping pong” model of reciprocating bigeminy to explain this unusual electrocardiographic pattern, based on two or more sites in the distal His-Purkinje system with different heart rate thresholds for developing ventricular bigeminy (figure below). In the proposed scenario: i) when the heart rate exceeds the threshold of the first site, ventricular bigeminy develops, causing the heart rate to accelerate and exceed the threshold of the second site for bigeminy; ii) the triggered beat from the first site thus induces a triggered beat from the second site; iii) the triggered beat from the second site then induces a triggered beat from the first site, and so forth. We show in a computer model of the anatomic rabbit ventricles that this ‘ping pong’ mechanism of reciprocating bigeminy readily produces the characteristic electrocardiographic pattern of BVT, and its degeneration to polymorphic VT when additional sites develop bigeminy.
- © 2010 by American Heart Association, Inc.