LEFT-VENTRICULAR END-SYSTOLIC ELASTANCE IS INCORRECTLY ESTIMATED BY THE USE OF STEPWISE AFTERLOAD VARIATIONS IN CONSCIOUS, UNSEDATED, AUTONOMICALLY INTACT DOGS

Background End-systolic elastance (E(es)), the slope parameter of the end-systolic pressure (ESP)-volume (ESV) relation (ESPVR), is usually estimated in patients by producing stepwise, steady-state pharmacologi cal afterload variations and collecting one ESP-ESV point from each st ep. The ESPVR is then constructed by fitting a linear equation to thes e points. In sedated, autonomically blocked dogs, it has been shown th at when one point from control, one point from a state of increased af terload, and one point from a state of decreased afterload are used, t he resulting E(es) incorrectly estimates true E(es), defined as the sl ope of the ESPVR obtained by transient vena caval occlusion. We invest igated if this was also the case in unsedated, autonomically intact do gs when the points used belonged to steady states of progressively dec reasing or progressively increasing afterload pressure. Methods and Re sults In 10 conscious dogs instrumented with left ventricular (LV) end ocardial sonomicrometers to measure LV volume, a LV pressure transduce r, and an inferior vena caval (IVC) occluder, two protocols were carri ed out on separate days. In each protocol, an ESPVR was generated by I VC occlusion in the control state and in two steady-state levels of af terload change produced by stepwise infusion of nitroprusside (protoco l 1, afterload decrease) and angiotensin II (protocol 2, afterload inc rease). In each protocol, steady-state ESP-ESV data points were averag ed from the control state and from each level of afterload variation. Linear equations were fitted to the three steady-state points from eac h protocol, and the estimated E(es) values obtained (E(es)EST) were co mpared with the E(es) values of the control ESPVRs obtained by IVC occ lusion (E(es)TRUE). In protocol 1, E(es)EST underestimated E(es)TRUE b y about 16% (E(es)EST, 6.49+/-1.55 mm Hg/mL; E(es)TRUE, 7.48+/-1.29 mm Hg/mL; P<.02). In protocol 2, E(es)EST overestimated E(es)TRUE by abo ut 37% (E(es)EST, 9.99+/-3.97 mm Hg/mL; E(es)TRUE, 6.43+/-3.88 mm Hg/m L; P<.007). Conclusions In conscious, autonomically intact dogs, the u se of stepwise, steady-state afterload variations to obtain ESP-ESV da ta points to construct the ESPVR incorrectly estimates E(es). In the c ase of afterload reduction, E(es)TRUE is underestimated an average of 16.3%, and in the case of afterload increase, E(es)TRUE is overestimat ed an average of 37.1%. These errors should be taken into account when interpreting clinical studies using this methodology.