LABORATORY INVESTIGATION ELECTROPHYSIOLOGY Electrophysiologic effects of papillary muscle traction in the intact heart

In this study we used transmural multipolar electrodes, sonomicrometers implanted within the left ventricular wall, and cardiac electrical stimulation techniques to examine the effect of transient mechanical posterior papillary muscle traction on local myocardial electrophysiologic characteristics. Nine open-chest dogs were atrially paced (cycle length 400 msec) followed by insertion of timed premature extrastimuli at left ventricular epicardial pacing sites either in the vicinity of (traction zone) or remote from (nontraction zone) the site of papillary muscle traction. Electrophysiologic recordings were made before and during periods of intermittent papillary muscle traction of predetermined timing, application rate (25 cm/sec), and duration (170 msec). Papillary muscle traction was applied in late diastole just before the last beat of each atrial drive train. In seven of nine dogs application of transient papillary muscle traction resulted in significantly earlier local ventricular activation (mean activation advancement 30 ± 13 msec), altered QRS morphology of the last conducted atrial drive-train beat, and relative prolongation of ventricular functional refractory period in the traction zone. Conversely, in nontraction zones in these seven dogs, early activation did not occur and refractoriness remained unchanged as tested by a locally placed extrastimulus. In two of nine dogs traction failed to induce early activation and changes in refractoriness did not occur. Alterations in regional myocardial blood flow (assessed by radioactive microsphere technique) did not appear responsible for the observed changes, since there was no demonstrable traction-induced difference in regional blood flow between the traction and nontraction zones. Thus, in normal myocardium in situ, regional abnormal wall motion may be associated with alterations of local ventricular activation and refractoriness, factors that in the diseased heart may lead to increased susceptibility to arrhythmias. Circulation 73, No. 5, 1013-1021, 1986. ALTHOUGH an association between abnormal regional myocardial mechanical function and development of potentially lethal ventricular arrhythmias has become well recognized clinically,'-9 the basis of this relationship in the intact heart is not understood. In superfused cardiac tissues, experimental studies have demonstrated that myocardial length/tension relationships influence transmembrane action potential characteristics."'--3 Additionally, in isolated perfused From the Veterans Administration Medical Center and Departments of Medicine and Surgery, University of Minnesota Medical School, Minneapolis. This study was funded by a grant-in-aid and fellowship grant from the American Heart Association, Minnesota Affiliate, and NRSA-NIH HL06772 (Dr. Gomick), and by grant 1R23-HL29460 (Dr. Benditt) from the National Institutes of Health. The study was completed during Dr. Benditt's tenure as an Established Investigator of the American Heart Association. Address for correspondence: Charles C. Gornick, M.D., Cardiology Section 11 IC, Veterans Administration Medical Center, 54th St. and 48th Ave. South, Minneapolis, MN 55417. Received July 23, 1985; revision accepted Feb. 13, 1986. Vol. 73, No. 5, May 1986 whole heart preparations,t2 13 alterations in shortening or tension development have been shown to alter transmembrane action potential repolarization. Similarly, diastolic transmembrane potential depolarization, initiating a new action potential, has been observed during periods of transient stretch in isolated cardiac tissue.12' 13 However, it is not known whether disturbances of myocardial contraction or abnormal stretch on portions of the ventricular wall alter myocardial electrophysiologic characteristics, and thereby potentially increase arrhythmia susceptibility in the diseased heart in situ. The purpose of this study was to determine, in vivo, whether transient mechanically applied traction to the posterior papillary muscle is accompanied by potentially arrhythmogenic alterations of local ventricular electrophysiologic properties. To this end, we measured local endocardial and epicardial electrophysiologic characteristics in the vicinity of the posterior 1013 by gest on Sptem er 6, 2017 http://ciajournals.org/ D ow nladed from