50th Anniversary - Historical Article - Demonstration of the mechanism of transient entrainment and interruption of ventricular tachycardia with rapid atrial pacing (Reprinted from Journal of the American College of Cardiology, February 1984)

An unusual case is presented in which ventricular tachycardia at a rate of 141 beats/min was transiently entrained by rapid atrial pacing at rates of 150, 155 and 160 beats/min, and was interrupted by rapid atrial pacing at a rate of 165 beats/min. During each period of transient entrainment, consta nt ventricular fusion beats were present except for the last entrained beat , and progressive ventricular fusion (different fusion QRS complexes) was d emonstrated when comparing QRS complex configurations during transient entr ainment at each pacing rate. Interruption of the ventricular tachycardia wa s associated with localized conduction block to the right ventricular recor ding site, followed by activation of that site from a different direction a nd with a shorter conduction time by the subsequent pacing impulse. These d ata clearly distinguish transient entrainment of a tachycardia from overdri ve suppression of a tachycardia, and strongly suggest that reentry was the underlying mechanism of the ventricular tachycardia.