[Inotropic effect of rhythm dispersion]

The influence of rhythm dispersion on the mean amplitude of rat and rabbit papillary muscle contractions and isovolumic contractions of canine heart has been investigated. In rabbit ventricular myocardium which shows a steep force-frequency relationship in the 0.3--1.0 s-1 range of frequencies, the increased rhythm dispersion of stimulation produces a rise in the mean amplitude of contractions. The inotropic effect of rhythm dispersion is more pronounced at higher frequencies of stimulation. The inotropic effect of activation may reach 30-40%. The increased rhythm dispersion reduces the mean value of systolic pressure in isovolumic canine heart. It is suggested that the inotropic effect of rhythm dispersion may be due to non-linearity of the force-frequency relationships.