Force-frequency relationship and inotropic stimulation in the nonfailing and failing human myocardium: implications for the medical treatment of heart failure

In isolated papillary muscle strips from nonfailing donor hearts (NF) and from the hearts of patients with dilated cardiomyopathy with severe heart failure (NYHA IV), the force-frequency relationship was studied. Experiments were performed under basal conditions and in the presence of 0.01 μM or 0.1 μM isoprenaline and 0.02 μM ouabain. In NF, there was a positive inotropic effect following an increase of the stimulating frequency, whereas in NYHA IV, the force gradually declined under these conditions. Low concentrations (0.01) μM of isoprenaline prevented the negative inotropic effect in NYHA IV, whereas at 0.1 μM the mechanical function deteriorated in NF and NYHA IV. Ouabain had no effect on the force-frequency relationship compared to basal conditions. It is concluded that a reduction of high frequencies does improve the contractility in the failing myocardium. It is not unreasonable to speculate that this mechanism might be involved in the beneficial effects of drugs which reduce the heart rate, such as β-adrenoceptor antagonists and cardiac glycosides, in the condition of congestive heart failure in which the sympathetic tone is high.