Anterior and posterior left ventricular sarcomere lengths behave similarly during ejection

J. M. Guccione, W. G. O'Dell, A. D. McCulloch, W. C. Hunter
1997 American Journal of Physiology. Heart and Circulatory Physiology  
Anterior and posterior left ventricular sarcomere lengths behave similarly during ejection. Am. J. Physiol. 272 (Heart Circ. Physiol. 41): H469-H477, 1997.-Previous studies of regional differences in myocardial deformation between the anterior and posterior walls of the canine left ventricle were based on strain, which is not an absolute measure of deformation. We thus compared sarcomere lengths at anterior and posterior sites during ejection in isolated dog hearts. Cineradiographic imaging of
more » ... graphic imaging of regional deformation with radiopaque markers implanted near the midwall in five hearts and just below the epicardium in six hearts, combined with postmortem histology, allowed sarcomere length reconstruction throughout the cardiac cycle. The amount of sarcomere shortening accompanying left ventricular ejection was similar in both walls of the left ventricle for sarcomeres located at epicardial and midwall sites. The mean sarcomere length (taken at the middle of the ejecting range) was also similar between the anterior and posterior sites when averaged over all hearts. The similarity of sarcomere function held not only at end systole but throughout ejection and over wide ranges of ventricular pre-and afterloads. Hence functional measurements of relative myocardial shortening may not be indicative of regional sarcomere length heterogeneity. strain; myocardium; ventricular function REGIONAL DIFFERENCES in the patterns of myocardial deformation between the anterior, lateral, and posterior walls of the canine left ventricle have been observed (3, 17). This is not surprising because the beating heart is a complex three-dimensional (3-D) and fiber-wound structure with mechanical properties that are nonlinear, anisotropic, time varying, and probably spatially inhomogeneous. These previous studies were based on a description of deformation in a limited region of the wall by means of strain tensors. A tensor description of strain provides information on relative stretches in any direction. However, strain is not an absolute measure of deformation because it is measured relative to an arbitrary reference configuration such as end diastole. Recently, our laboratory developed a method that allows the "reconstruction" of absolute sarcomere lengths (SLs) and orientations at any transmural layer in the left ventricular wall during any phase of the cardiac cycle (11). It is not possible with current techniques to observe directly the in vivo behavior of sarcomeres in the beating heart. Until this method was developed, the only techniques used for measuring SLs transmurally involved histological procedures on hearts fixed at specific left ventricular pressures so as to simulate different nonsystolic states in the cardiac cycle. Relative strain analyses in the anterior and posterior walls of the left ventricle were correlated with histological measurements by Villarreal and Lew (17) and Fann et al. (31, who measured the fiber orientations and related these fiber directions to the direction of maximum strain. These studies did not, however, attempt to measure absolute SLs or correct precisely for any artifactual deformation arising from the histological procedures. We thus examined the canine left ventricle for potential regional differences in sarcomere function during ejection. We compared SLs reconstructed at posterior and anterior sites at different transmural depths in beating canine hearts operating under a wide range of hemodynamic loads. SL was reconstructed by combining cineradiography of local deformations with postmortem histology of the same region.
doi:10.1152/ajpheart.1997.272.1.h469 pmid:9038969 fatcat:rbcqrbhmfbacpj6knb52fc5ksq