Omecamtiv mecarbil evokes diastolic dysfunction and leads to periodic electromechanical alternans

Omecamtiv mecarbil (OM) is a promising novel drug for improving cardiac contractility. We tested the therapeutic range of OM and identified previously unrecognized side effects. The Ca2+ sensitivity of isometric force production (pCa(50)) and force at low Ca2+ levels increased with OM concentration in human permeabilized cardiomyocytes. OM (1 mu M) slowed the kinetics of contractions and relaxations and evoked an oscillation between normal and reduced intracellular Ca2+ transients, action potential lengths and contractions in isolated canine cardiomyocytes. Echocardiographic studies and left ventricular pressure-volume analyses demonstrated concentration-dependent improvements in cardiac systolic function at OM concentrations of 600-1200 mu g/kg in rats. Administration of OM at a concentration of 1200 mu g/kg was associated with hypotension, while doses of 600-1200 mu g/kg were associated with the following aspects of diastolic dysfunction: decreases in E/A ratio and the maximal rate of diastolic pressure decrement (dP/dt(min)) and increases in isovolumic relaxation time, left atrial diameter, the isovolumic relaxation constant Tau, left ventricular end-diastolic pressure and the slope of the end-diastolic pressure-volume relationship. Moreover, OM 1200 mu g/kg frequently evoked transient electromechanical alternans in the rat in vivo in which normal systoles were followed by smaller contractions (and T-wave amplitudes) without major differences on the QRS complexes. Besides improving systolic function, OM evoked diastolic dysfunction and pulsus alternans. The narrow therapeutic window for OM may necessitate the monitoring of additional clinical safety parameters in clinical application.

Automated summary

Omecamtiv mecarbil (OM) is a promising novel drug for improving cardiac contractility, but may have previously unrecognized side effects. Concentration-dependent improvements in cardiac function were observed with OM, although higher concentrations were associated with hypotension and diastolic dysfunction.