Coupling interval from slow to tachycardiac pacing decides sustained alternans pattern

Abstract

We discovered that the coupling beat interval from a slow to a tachycardiac pacing period considerably affected the pattern of the beat-to-beat alternation of the tachycardia-induced sustained contractile alternans. We analyzed the relationship between the coupling interval and the pattern and amplitude of the alternans in the isovolumic left ventricle of canine blood-perfused hearts. The alternans pattern and amplitude varied transiently over the first 30–50 beats and became gradually stable over the first minute in all 12 hearts. We discovered that stable alternans, even under the same tachycardiac pacing, had three different strong-weak beat patterns depending on the coupling interval. A relatively short coupling interval produced a representative sustained alternans of the strong and weak beats. A relatively long coupling interval produced a similar sustained alternans but in a reversed order of even- and odd-numbered beats counted from the coupling interval. However, sustained alternans disappeared after 1–3 specific coupling intervals. We conclude that ventricular pacing rate does not solely determine the pattern and amplitude of sustained contractile alternans induced by tachycardia.