Entrainment of ventricular tachycardia by AV nodal reentrant tachycardia.

Endocardial recordings from a patient with both sustained ventricular tachycardia and AV nodal reentrant tachycardia are presented that demonstrate spontaneous transient entrainment of ventricular tachycardia by AV nodal reentrant tachycardia. During electrophysiological catheterization, there were repeated episodes of spontaneous conversion from a wide to a narrow QRS morphology following the induction of ventricular tachycardia. With conversion from the wide to the narrow QRS, the ventricular deflection in the coronary sinus electrograms demonstrated an abrupt change in morphology, indicating a change in activation sequence at this site from the wavefront of depolarization emerging from the ventricular tachycardia circuit to a wavefront conducting over the His-Purkinje system. However, the right ventricular apex electrogram demonstrated a constant morphology with a decrease in cycle length equal to that of the other intracardiac electrograms, indicating a constant direction of activation from the ventricular tachycardia circuit, and that ventricular tachycardia had been transiently entrained by AV nodal reentrant tachycardia. In addition, rapid atrial pacing during ventricular tachycardia narrowed the QRS and demonstrated transient entrainment of the right ventricular apex electrogram. Although transient entrainment of a tachycardia is evidence supporting reentry with an excitable gap as the probable mechanism, its demonstration has required the use of rapid pacing techniques. This case is a spontaneously occurring example of transient entrainment of one tachycardia circuit by another, a phenomenon that has not been previously described.