A Note on the Influence of Asynchronous Activation on Myocardial Contraction

Publisher Website
Google Scholar
Abstract
Pairs of rabbit papillary muscles were mounted in series to make it possible to study the effects of asynchronous activation on myocardial contraction. The two muscles were connected together via platinum loops hooked to a lever (displacement transducer), the other end of each muscle being fixed to a force transducer. The force of each muscle was measured at various contraction frequencies with the lever fixed (isometric contractions) or freely movable (auxotonic contractions). With auxotonic contractions, asynchronous activation (25 or 50 ms interval between stimulation of the two muscles) increased the movements of the muscles, decreased their force, and prolonged the duration of the contraction at 37°C. These effects were greater, the higher the contraction frequency within the range 30–150 beats/min. On the basis of these results, it is suggested that the physiological asynchrony of the myocardial contraction in vivo tends to offset frequency‐induced changes at the cellular lever (enhanced intensity of active state, shortening of active state duration).