Omecamtiv mecarbil attenuates length-tension relationship in healthy rat myocardium and preserves it in monocrotaline-induced pulmonary heart failure

Effects of omecamtiv mecarbil and mavacamten in isolated human atrium

Heart failure is a syndrome that can result from impaired heart muscle contractions like in dilative cardiomyopathy but also from hypertrophic obstructive cardiomyopathy (HOCOM). A pharmacological therapy might lie in Ca²⁺-sensitizing or Ca²⁺-desensitizing drugs, respectively. Such drugs are thought to be omecamtiv mecarbil (OME) and mavacamten (MYK-461), respectively. Their function in contracting human muscle is not fully understood and was the focus of the present study. OME from 1 nM to 10 µM cumulatively applied failed to raise force of contraction in human right atrial preparations strips (HAP) or mouse left atrial preparations (LA). However, OME prolonged time to peak tension and time of relaxation in HAP and LA but did not alter the beating rate in right atrial preparations from mice (RA). In contrast, MYK-461 (10 nM to 10 µM) reduced concentration- and time-dependently force of contraction in HAP and LA. MYK-461 (10 µM) did not affect the beating rate in RA. In summary, the present data failed to detect an increase in force of contraction for OME, in human and mouse atrium. In contrast, a Ca²⁺ desensitizer studied for comparison was able to reduce force of contraction in HAP and LA. We conclude that putative beneficial effects of OME in dilated cardiomyopathy cannot be explained by positive inotropic effects in the HAP, whereas beneficial functional effects of MYK-461 in HOCOM can be explained by negative inotropic effects in HAP.

The right ventricle in tetralogy of Fallot: adaptation to sequential loading

Right ventricular dysfunction is a major determinant of outcome in patients with complex congenital heart disease, as in tetralogy of Fallot. In these patients, right ventricular dysfunction emerges after initial pressure overload and hypoxemia, which is followed by chronic volume overload due to pulmonary regurgitation after corrective surgery. Myocardial adaptation and the transition to right ventricular failure remain poorly understood. Combining insights from clinical and experimental physiology and myocardial (tissue) data has identified a disease phenotype with important distinctions from other types of heart failure. This phenotype of the right ventricle in tetralogy of Fallot can be described as a syndrome of dysfunctional characteristics affecting both contraction and filling. These characteristics are the end result of several adaptation pathways of the cardiomyocytes, myocardial vasculature and extracellular matrix. As long as the long-term outcome of surgical correction of tetralogy of Fallot remains suboptimal, other treatment strategies need to be explored. Novel insights in failure of adaptation and the role of cardiomyocyte proliferation might provide targets for treatment of the (dysfunctional) right ventricle under stress.