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.

Postextrasystolic Contractility Normally Decays in Alternans in Canine In Situ Heart

“…The present pacing rates were much lower than the pacing rates (250-300 beats/min) that caused sustained alternans in excised, cross-circulated canine hearts [22]. Besides, we have already found that the PES contractility alternans decay consistently exists within the heart rate range of 100-150 beats/min produced by para-Hisian pacing after atrioventricular block in the excised, cross-circulated normal canine hearts under physiological conditions [9].…”

“…The pacing rate was set at 163Ϯ36 beats/min (range: 90-200 beats/min) slightly above the spontaneous sinus rates in the respective hearts. These pacing rates were higher on average than the sinus rates (60-120 beats/min) in conscious dogs, but still much lower than 250-300 beats/min that could cause sustained alternans in the normal excised, cross-circulated canine hearts [22]. The anesthesia per se did not suppress canine cardiac conditions to the extent that the sustained PES alternans could occur even at the present pacing rate [7,23].…”

Triggered alternans in an ionic model of ischemic cardiac ventricular muscle

“…7. Apart from the triggered ischemic alternans men-tioned above, the only other two instances of ͕1:1↔2:2͖ bistability of which we are aware occur in the mechanical contraction of the heart [78][79][80] and in periodic driving of modified forms of the space-clamped Beeler-Reuter equations. [22][23][24] In the latter case, the behavior is different from ours, in that the 2:2 cycle is made up of two full-sized action potentials ͓compare, e.g., the inset in Fig.…”

“…5,6,8 There is also evidence for this bistability ͑indeed, perhaps multistability or neutral stability͒ during mechanical alternans of the nonischemic ventricle. [78][79][80] Thus, by our definition of triggered alternans, it is important to rule out the possibility that there is a pre-existing very-low-amplitude alternans present ͓see, e.g., Fig. 3 of Ref.…”

“…Fourth, bistability has been described between two different 2:2 rhythms in frog ventricle, 32 and a bistability or multistability or neutral stability between 2:2 rhythms has been described in the mechanical activity of the dog heart. [78][79][80] This bistability has also been treated in terms of a single-branched one-dimensional map. 27 In addition, as detailed above, concordant and discordant alternans can be viewed as coexisting 2:2 rhythms.…”