Mechano-electrical feedback.

Abstract

See article by Nanthakumar et al. [6] (pages 303–309) in this issue. During the last two decades, there has been growing interest in the effect that mechanical heart disorders have on the heart's electrophysiological properties. It has been shown in numerous animal experiments that myocardial stretch produced by volume or pressure overload or direct distension of a muscle strip leads to significant electrophysiological changes [1,2]. This interaction, which has been termed mechano-electrical feedback (MEF), is a concept that undoubtedly has evolved into an accepted mechanism today. MEF describes electrophysiological changes caused by changes in myocardial segment length. These changes most notably include: (1) a shortening of the action potential duration (APD), (2) a decrease in the resting diastolic potential, (3) a decrease in the maximum systolic action potential amplitude, (4) development of early afterdepolarizations, (5) ectopic beats originating from afterdepolarization in myocardium sustaining the greatest stretch (reaching threshold for depolarization first), (6) and other contour changes of the cardiac action potential. Most prior studies on MEF have examined the effect of in creases in mechanical load (stretch) on the cardiac action potential duration and configuration while fewer studies have investigated the effect of ventricular un loading. In most studies, the monophasic action potential (MAP) recording method was used to evaluate alterations in local action potential characteristics subsequent to changes in myocardial loading or segment length. Also, in the majority of these studies, MEF has been measured under conditions of excessive, unphysiologic loading or stretch of myocardium in experimental animals. Human studies addressing MEF also have focussed on unphysiological conditions, such as compression/decompression of the left ventricle during cardiopulmonary bypass surgery [3], transient aortic occlusions [4] or aortic balloon angioplasty [5]. To date, direct evidence for mechano-electrical feedback in the human heart under conditions that may mimic real-life … * Tel.: +1-202-745-8398; fax: +1-202-745-8184 mfranz{at}washington.va.gov