Calcium Responsiveness in Canine Pacing-induced Heart Failure

The specific lesion(s) and potential compensatory alterations of excitation–contraction coupling in heart failure are not clear in detail. We therefore subjected five dogs to 2–5 weeks of rapid ventricular pacing until heart failure developed. Data obtained from these five dogs with pacing-induced heart failure were compared to data from six healthy controls. Under anesthesia,in situsteady state responses of regional contractile function to intracoronary calcium infusion were established. Maximal calcium-activated regional contractile function in dogs with heart failure was 46% less than in controls; calcium sensitivity was unchanged [pCa502.55±0.31v2.82±0.17 (± )]. Our data point to a decrease in maximal calcium-activated force and an unchanged calcium sensitivity if an unchanged calcium transient is assumed, or a compensatory increase in calcium sensitivity of failing myocardium if a decreased calcium transient is assumed.