Postextrasystolic contractile decay always contains exponential and alternans components in canine heart

Abstract

In isolated, blood-perfused canine hearts, postextrasystolic potentiation (PESP) decays monotonically after a noncompensatory pause following a spontaneous extrasystole (ES). The monotonic PESP decay yields myocardial internal Ca(2+) recirculation fraction (RF). We have found that after a compensatory pause (CP), PESP decays in alternans, consisting of an exponential and a sinusoidal decay component. We have proposed that this exponential component also yields RF. In the present study, we examined the reliability of this alternative method by widely changing the ES coupling interval (ESI), CP, and heart rate in the canine excised, cross-circulated left ventricle. We found that all PESP decays consisted of the sum of an exponential and a sinusoidal decay component of variable magnitudes whether a CP existed or not. Their decay constants as well as the calculated RF were independent of the ESI and CP. This confirmed the utility of our alternative RF determination method regardless of the ESI, CP, and heart rate. Direct experimental evidence of Ca(2+) dynamics supportive of this alternative method, however, remains to be obtained.

Exponential Fitting of Postextrasystolic Potentiation May Underestimate the Cardiac Ca2+ Recirculation Fraction: A Theoretical Analysis

“…There, the monotonic decay however did not warrant the exponential decay. The alternans became obvious as the beat intervals decreased to 600, 500, and 400 ms by para-Hisian ventricular pacing whether or not a compensatory pause existed [17]. Exceptionally, PESP showed reasonable decay exponentially when an extrasystole interpolated the natural sinus rhythm [23,25].…”

“…The second term is an exponential component with an oscillatory decay. Coefficients a and b are the amplitude constants of the exponential and oscillatory decay components of the first PESP beat [1,2,17,18]. Coefficients a and b were also normalized relative to the regular-beat contractility level.…”

“…Denominator e is the beat constant of the exponential decay of the exponential component of PESP [1,2,17,18]. Denominator s is the beat constant of the exponential decay of the oscillatory decay component of PESP.…”

“…e and s were expressed as number of PESP beats, but not in seconds (s). Therefore, we have decided to call e and s beat constants instead of time constants [1,2,17,18]. However, conversion between the beat and time constants is simple.…”

“…Here, we used aϭ0.5, e ϭ2, and s ϭ0.8 as the representative values for regular beat intervals of 400-600 ms and extrasystolic beat intervals of 300-400 ms in our previous observations [11,12,17]. Furthermore, we increased b from 0 in steps of 0.1 and stopped it at 0.5 (ϭa) although our previous observations have shown that alternans PESPs obviously have bՆa [11,12,17]. In other words, PESPs with bϾa appeared so obvious that no one would dare to fit an exponential curve to it.…”