Mechano-electrical feedback
Authors: M Franz
Journal: Cardiovascular Research (2000)

perimental animals.Human studies addressing MEF also in this issue.have focussed on unphysiological conditions, such as compression / decompression of the left ventricle during cardiopulmonary bypass surgery [3], transient aortic occlu-1.Introduction sions [4] or aortic balloon angioplasty [5].To date, direct evidence for mechano-electrical feedback During the last two decades, there has been growing in the human heart under conditions that may mimic interest in the effect that mechanical heart disorders have real-life clinical or physiological scenarios, has been on the heart's electrophysiological properties.It has been scarce.In that regard, the study by Nanthakumar et al. [6] shown in numerous animal experiments that myocardial in this issue of the journal is a welcome addition.The stretch produced by volume or pressure overload or direct authors used a novel and noninvasive approach for estimatdistension of a muscle strip leads to significant electro-ing changes in ventricular repolarization during the physiophysiological changes [1,2].This interaction, which has logical maneuvers of Valsalva and tilt-table testing.A been termed mechano-electrical feedback (MEF), is a previously implanted stimulus to T wave (Stim-T) sensing concept that undoubtedly has evolved into an accepted pacemaker was used to assess repolarization intervals in mechanism today.MEF describes electrophysiological the apical region of the right ventricle.They were able to changes caused by changes in myocardial segment length.discern a minor lengthening of RV apical repolarization These changes most notably include: (1) a shortening of when RV volume was changed by Valsalva and head-up tilt the action potential duration (APD), (2) a decrease in the testing.Even after blockade of autonomic reflexes by the resting diastolic potential, (3) a decrease in the maximum combined administration of atropin and propanolol and systolic action potential amplitude, (4) development of keeping heart rate constant by external transthoracic early afterdepolarizations, (5) ectopic beats originating pacing, these changes, while miniscule, remained statistifrom afterdepolarization in myocardium sustaining the cally significant.This observation lends further credence to greatest stretch (reaching threshold for depolarization first), the existence of MEF in the human heart.Even more so as ( 6) and other contour changes of the cardiac action it was obtained by noninvasive methods (lest the fact that potential.Most prior studies on MEF have examined the it required prior pacemaker implantation) and relied on a effect of increases in mechanical load (stretch) on the sensor which differed from the MAP technique normally cardiac action potential duration and configuration while used to ascertain such repolarization effects.These obfewer studies have investigated the effect of ventricular servations do not, however, provide added insight into unloading.In most studies, the monophasic action po-potential arrhythmic mechanisms of MEF in humans.It is tential (MAP) recording method was used to evaluate noteworthy that the authors did not make such claim.alterations in local action potential characteristics subsequent to changes in myocardial loading or segment 1.1.Minimal changes in repolarization length.Also, in the majority of these studies, MEF has been measured under conditions of excessive, un-The degree of changes in repolarization observed in the physiologic loading or stretch of myocardium in ex-study by Nanthakumar et al. [6] was extremely small.It amounted to 1.160.7% of baseline, which translates into roughly 4 ms shortening from the baseline duration of 370