ASSESSMENT OF REGIONAL MYOCARDIAL PERFORMANCE WITH END-SYSTOLIC PRESSURE LENGTH AND THICKNESS RELATIONSHIPS

Although end-systolic pressure length and thickness relationships (ESP LR, ESPTR) are now widely used as substitutes for the end-systolic pre ssure volume relationships, there are some reservations about their us e as an index of left ventricular (LV) performance. This study address ed three issues, namely: (I) which loading technique (decreasing prelo ad by inferior vena cava (IVC) balloon occlusion or increasing systoli c pressure by aortic constriction) is the most likely to yield usable data; (2) reproducibility of these relationships over a 30 min period; and (3) whether by using end-ejection (zero aortic flow) as a definit ion of end-systole, ESPLR and ESPTR can be used to characterize myocar dial performance independent of load. Thirteen anesthetized beagles, w eighing 16-25 kg, were used for this study, and were instrumented with sonomicrometers. We found that when ESPLR and ESPTR were constructed from data derived during aortic constriction, the slopes of these rela tionships were steeper and more curvilinear than when they were constr ucted from data recorded during IVC occlusion. In addition, the mean d ifference between ESPLR, ESPTR obtained 30 min apart was small, althou gh there was a fair degree of variability between the first and second measurements. Using end-ejection to define end-systole, both ESPLR an d ESPTR were relatively insensitive to loading conditions (LV end-dias tolic pressure of 8-12 mmHg and 14-18 mmHg, aortic systolic pressure o f 7-10 mmHg and 20-25 mmHg above baseline (in terms of the slope and s hift (leftward or rightward) in these relationships, but were sensitiv e to inotropic interventions (dobutamine 2.5 mu g/kg per min and 5 mu g/kg per min). We conclude that, ESPLR and ESPTR, defined from measure ments at end-ejection, can be used as adequate descriptors of regional myocardial performance if they were constructed from data over a simi lar pressure range during IVC balloon occlusion.