Contraction-excitation feedback in myocardium. Physiological basis and clinicl relevance

Abstract

Excitation-contraction coupling in ventricular myocardium has received exhaustive investigation. Feedback processes in the reverse direction between contraction and excitation are less conspicuous and, not surprisingly, have attracted little notice despite their potential physiological and clinical importance. For the present, contraction-excitation feedback is inferred when changes in mechanical stress or strain cause or precede changes in membrane potential. For example, reduced force development or increased shortening can induce greater depolarization. Contraction-excitation feedback, according to the type and timing of the mechanical change producing it, can appear either as a prolongation of an action potential, or as a transient depolarization. This review will describe the circumstances under which contraction-excitation feedback occurs, discuss possible explanations for the phenomenon, and speculate on its potential importance in selected clinical situations.