Alternans Decay of Postextrasystolic Potentiation in Human Left Ventricle

Abstract

One of the present authors, H. Suga, and his group have developed an integrative analysis method to assess the total amount of myocardial Ca 2ϩ handled in the excitation-contraction coupling in beating canine hearts [1][2][3][4][5][6]. This method requires that the intramyocardial Ca 2ϩ recirculation fraction (RF) and the left ventricular (LV) O 2 consumption for the excitationcontraction coupling both be measured in a beating heart [1][2][3][4][5][6]. The RF has conventionally been calculated from the exponential decay rate of the postextrasystolic (PES) potentiated E max [7,8]. However, against general expectations [7,8], Suga's group has found that the LV PES E max generally decays in alternans in canine hearts under both physiological and pathological conditions [1][2][3][4][5][6]9]. Nevertheless, they succeeded in extracting an exponential decay component from the PES E max alternans decay by peeling off the oscillatory component. They obtained the RF from the exponential decay component and then the total amount of Ca 2ϩ handled in the excitation-contraction coupling [1][2][3][4][5][6].We expected that the same approach successfully applied to the beating canine heart would also be applicable to the human heart. We first investigated in patient LVs whether the PES E max would decay in alternans or exponentially. Although the PES potentia- Japanese Journal of Physiology, 54, 87-91, 2004 Key words: arrhythmia, E max , calcium, recirculation fraction. Abstract:An organ-level assessment of the total Ca 2ϩ handled in the excitation-contraction coupling in a beating heart has been accomplished in canine left ventricles (LVs). This approach combines the intramyocardial Ca 2ϩ recirculation fraction (RF) with the cardiac O 2 consumption for the excitation-contraction coupling. The RF has conventionally been obtained from the exponential decay of the postextrasystolic (PES) potentiation of myocardial contractility. However, in canine LVs, the PES contractility in terms of E max (end-systolic pressure-volume ratio) has been shown to decay generally in alternans under both physiological and pathological conditions. Nevertheless, the RF can be obtained from the exponential decay component in the PES E max alternans decay. We expected that the same Ca 2ϩ assessment could be applied to the human heart. As the first step, we investigated whether the PES E max would decay in alternans or exponentially in patient LVs. We retrospectively analyzed 13 patient cases that had stable regular beats unexpectedly interrupted by a spontaneous extrasystole followed by a PES compensatory pause during their diagnostic examination. These patients had either mitral regurgitation, old myocardial infarction, or dilated cardiomyopathy. Their LV E max decayed consistently in alternans within the first several PES beats. These E max alternans decays resemble those reported in canine LVs. This finding suggests for the first time the applicability of the same organ-level RF assessment method developed for canine hearts to human hearts. [The J...

Relative Refractoriness of Left Ventricular Contraction Underlies Human Tachycardia‐Induced Mechanical and Electrical Alternans

“…Theoretically, MA starts with an increase or a decrease of contractile force and sustains by maintaining the change in an alternating manner . We hypothesized that (1) patients with MA have a steep mechanical restitution curve and are prone to develop an initial change of contractile force during tachycardia as shown in rodents and (2) patients with MA have a property to transform a strong contraction to a weak contraction in the subsequent beat and vice versa; consequently, the absolute value of the steepness of postextrasystolic potentiation (PESP) curve is equal to that of mechanical restitution curve, otherwise MA decays …”