Alternating cycle length during supraventricular tachycardia: what is the mechanism?

摘要

A 30-year-old female without structural heart disease was referred for electrophysiology study after 4 years of palpitations not controlled with medications. Baseline sinus cycle length was 765 ms, atrial-His (AH) interval 65 ms, and His-ventricular (HV) interval 46 ms. Atrial extrastimulus testing revealed evidence of antegrade dual AV nodal physiology with AH jump of 190 ms from 600/350 ms to 600/340 ms, but no sustained tachycardia. With infusion of isoproterenol, a regular, sustained, narrow-complex tachycardia, cycle length 340 ms, was repeatedly induced by atrial extrastimulus testing. Septal VA time was less than 50 ms, during and after spontaneous development of right-bundle-branch-block aberrancy. His-refractory premature ventricular extrastimuli did not affect the tachycardia. After cessation of overdrive ventricular pacing, the tachycardia continued with a V-A-V response, and the postpacing interval was 160 ms greater than tachycardia cycle length.