ANTERIOR AND POSTERIOR LEFT-VENTRICULAR SARCOMERE LENGTHS BEHAVE SIMILARLY DURING EJECTION

Previous studies of regional differences in myocardial deformation bet ween the anterior and posterior walls of the canine left ventricle wer e based on; strain, which is not an absolute measure of deformation. W e thus compared sarcomere lengths at anterior and posterior sites duri ng ejection in isolated dog hearts. Cineradiographic imaging of region al deformation with radiopaque markers implanted near the midwall in f ive hearts and just below the epicardium in six hearts, combined with postmortem histology, allowed sarcomere length reconstruction througho ut the cardiac cycle. The amount of sarcomere shortening accompanying left ventricular ejection was similar in both walls of the left ventri cle for sarcomeres located at epicardial and midwall sites. The mean s arcomere length (taken at the middle of the ejecting range) was also s imilar between the anterior and posterior sites when averaged over all hearts. The similarity of sarcomere function held not only at end sys tole but throughout ejection and over wide ranges of ventricular pre- and afterloads. Hence functional measurements of relative myocardial s hortening may not be indicative of regional sarcomere length heterogen eity.