Myocardial mechanical restitution and potentiation partly underlie alternans decay of postextrasystolic potentiation: simulation

We have reported that the postextrasystolic potentiation (PESP) decays in a lternans or monotonically, respectively, depending on whether the first pos textrasystolic beat interval has a compensatory pause or not, in the canine left ventricle. To get better mechanistic insight into the alternans PESP decay. we hypothesized that the myocardial mechanical restitution and poten tiation could partly account for both types of PESP decay, To test this hyp othesis, we simulated PESP decay on a computer using a documented equation combining myocardial mechanical restitution and potentiation. We changed th e first postextrasystolic beat interval after a fixed extrasystolic beat in terval without changing regular and other postextrasystolic beat intervals. The simulated PESP decayed in alternans or monotonically as a function onl y of the first postextrasystolic beat interval. Thus, the myocardial mechan ical restitution and potentiation could partly account for both alternans a nd monotonic decay of PESP. We conclude that myocardial mechanical restitut ion and potentiation may partly underlie the initial two alternating beats, the first beat being the most potentiated and the second beat being the mo st depressed, of alternans PESP decay in the canine heart.