Lack of postextrasystolic potentiation in a normal heart

Postextrasystolic potentiation. Do we really know what it means and how to use it?

Postextrasystolic potentiation (PESP), the increase in contractility that follows an extrasystole, is an interesting phenomenon that has been known for almost 100 years. The literature on this effect is reviewed. It is found that there is significant evidence that the phenomenon is independent of muscle loading and represents a distinct property of the myocardium. Examination of the literature pertaining to the cause of the effect suggests that calcium shifts within the sarcoplasmic reticulum are responsible, although there are some conflicts with this conclusion. Regarding the utility of PESP as a diagnostic test of latent viability of ischemic myocardium, the literature review reveals contradictions and conflicts with several methodological problems of the experiments. Finally, concerning the utility of continuous PESP (paired-pacing) to augment ventricular function in the failing ventricle, the studies again are inconclusive and methodologically suspect. Conditions for the proper analysis of the PESP response are reported, and suggestions for future studies are introduced.

Effects of verapamil on postextrasystolic potentiation

To assess the effects of verapamil on postextrasystolic potentiation (PESP), contrast left ventriculography was performed in ten healthy anesthetized dogs before and after the intravenous administration of verapamil, 0.1 mg/kg. During the contrast ventriculography, a single atrial premature stimulus was introduced. Ejection fractions of a control beat and postpremature beat were measured before and after verapamil. Before verapamil, the mean ejection fractions of the control beat and the postpremature beat were 60 +/- 10 percent and 67 +/- 10 percent, respectively (p less than 0.05). Following the administration of verapamil, the mean ejection fraction of the control beat decreased from 60 +/- 10 percent to 55 +/- 11 percent (p less than 0.05). However, the mean ejection fraction of the postpremature beats increased when compared with the control beats following intravenous verapamil (65 +/- 8 percent and 55 +/- 11 percent, respectively; p less than 0.05). These results suggest that PESP is not inhibited by the administration of intravenous verapamil.

Effect of diltiazem on spontaneous cyclic Ca2+ release from sarcoplasmic reticulum

We used saponin-treated skinned fibers isolated from papillary muscles of the right ventricle of guinea pigs to compare the effects of diltiazem on the spontaneous cyclic Ca2+ release from the sarcoplasmic reticulum (SR) of cardiac muscle with the effects of caffeine. Both diltiazem and caffeine increased the frequency of cyclic contractions in EGTA (ethyleneglycol-bis-(beta-aminoethylether) N,N,N',N'-tetra-acetate)-free solution and induced an incomplete, concentration-dependent relaxation of the muscle. The results suggest that the spectrum of the pharmacological effects of diltiazem on the SR is similar to that for caffeine, that is diltiazem accelerates the spontaneous Ca2+ release from the SR and suppresses Ca2+ reuptake by the SR, and that diltiazem as well as caffeine may act on the SR in vivo in a specific condition.