LEFT-VENTRICULAR REGIONAL MYOCYTE CONTRACTILITY IN NORMAL AND HEART-FAILURE STATES

Fundamental determinants of left ventricular (LV) pump performance are preload, afterload and myocyte contractility. Regional variability in LV end systolic wall stress, an important index of LV afterload, has been well defined in both control and congestive heart failure (CHF) s tates. The goal of this study was to examine end systolic wall stress and myocyte contractile function in three circumferential regions of t he LV in both control and CHF states. Accordingly, LV end systolic wal l stress and myocyte velocity of shortening were measured from the bas al, mid and apical regions in control pigs (n = 5) and following the i nduction of pacing-induced CHF (3 weeks, 240 beats/min, n = 5). LV mid wall, circumferential, end systolic wall stress decreased from base t o apex in both control (35 +/- 7 v 16 +/- 4 g/cm), P < 0.05) and CHF ( 155 +/- 23 v 92 +/- 24 g/ cm(2), P < 0.05) states. In the CHF group, L V end systolic wall stress was elevated by 300% compared to control va lues in all regions. LV myocyte velocity of shortening was equivalent in the basal and mid regions of control myocytes (52 +/- 2 v 57 +/- 2 m/s) and was higher in the apical region (63 +/- 3 mu m/s, P < 0.05). In the CHP group, LV myocyte velocity of shortening was reduced by 45% compared to controls with no regional variation. beta-adrenergic stim ulation increased myocyte velocity in both the control and CHF groups, however, regional variation was observed only in the CHF group. These unique results demonstrated that minimal regional variations in myocy te contractile function exist in both control and congestive heart fai lure states, and does not necessarily parallel patterns of regional LV end systolic wall stress. (C) 1997 Academic Press Limited.