Bidirectional ventricular tachycardia: ping pong in the His-Purkinje system.
BACKGROUND
Bidirectional ventricular tachycardia (BVT), which is characterized by an alternating beat-to-beat ECG QRS axis, is a rare but intriguing arrhythmia associated with digitalis toxicity, familial catecholaminergic polymorphic ventricular tachycardia (CPVT), and several other conditions that predispose cardiac myocytes to delayed afterdepolarizations (DADs) and triggered activity. Evidence from human and animal studies attributes BVT to alternating ectopic foci originating from the distal His-Purkinje system in the left and/or right ventricle, respectively.


OBJECTIVE
The purpose of this study was to evaluate a simple "ping pong" model of reciprocating bigeminy to explain BVT.


METHODS
We constructed a two-dimensional anatomic model of the rabbit ventricles with a simplified His-Purkinje system, in which different sites in the His-Purkinje system had different heart rate thresholds for DAD-induced bigeminy.


RESULTS
When the heart rate exceeded the threshold for bigeminy at the first site in the His-Purkinje system, ventricular bigeminy developed, causing the heart rate to accelerate and exceed the threshold for bigeminy at the second site. Thus, the triggered beat from the first site induced a triggered beat from the second site. The triggered beat from the second site next reciprocated by inducing a triggered beat from the first site, and so forth. Bigeminy from two sites produced BVT, and that from three or more sites produced polymorphic VT.


CONCLUSIONS
This "ping pong" mechanism of reciprocating bigeminy readily produces the characteristic ECG pattern of BVT and its degeneration to polymorphic VT if additional sites develop bigeminy.
Cardiovascular Research Laboratory, Department of Medicine (Cardiology), David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
Alex A
AA
Baher
Matthew
M
Uy
Fagen
F
Xie
Alan
A
Garfinkel
Zhilin
Z
Qu
James N
JN
Weiss
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002036:Bundle of His / Q000473:pathology / Q000503:physiopathology*; D003198:Computer Simulation; D004195:Disease Models, Animal; D004562:Electrocardiography; D006339:Heart Rate; D008953:Models, Anatomic; D011690:Purkinje Fibers / Q000473:pathology / Q000503:physiopathology*; D011817:Rabbits; D013610:Tachycardia / Q000473:pathology / Q000503:physiopathology; D017180:Tachycardia, Ventricular / Q000473:pathology / Q000503:physiopathology; D000098850:Polymorphic Catecholaminergic Ventricular Tachycardia