SINUSOIDAL AND EXPONENTIAL DECAYS OF POSTEXTRASYSTOLIC TRANSIENT ALTERNANS IN EXCISED BLOOD-PERFUSED CANINE HEARTS

We have recently reported that the postextrasystolic contractile potentiation decays in alternans after a compensatory pause in canine left ventricles even under normal coronary and contractile conditions. The transient alternans appears to consist primarily of a small-magnitude exponential decay and a large-magnitude sinusoidal decay. We, therefore, hypothesized that the contractility (y) of the postextrasystolic alternans beats (beat number x) could be expressed as y = a . exp[- (x - 1)/b] + c . exp[-(x - 1)/d] . sin [pi(x -0.5)] +y(o), where a and c are the normalized magnitudes (relative to the preceding regular beat) of the two exponential terms in the first postextrasystolic beat, b and d are their time constants, and y(o) is the normalized magnitude of the post-alternans regular beat (approximate to 1). The first exponential term represents the monotonic decay. The sine term multiplied by the second exponential term represents the alternating decay. Mathematical curve-fitting indicated: 1) the above equation very closely fitted the alternans data with a squared correlation coefficient of 0.9996 on average, 2) c was 7 times on average greater than a, indicating dominance of the sine component, 3) b and d were 2.5 and 1.0 beats on average, indicating a faster decay of the sine component, and 4) this b was comparable to the time constant of the exponential decay of the postextrasystolic potentiation after no compensatory pause. This study suggests that myocardium has a mechanism to switch the postextrasystolic potentiation between the exponential and alternans decays depending on the first postextrasystolic interval.