A Study of the Assessment of Left Vertricular Function in Non-Rheumatic Aortic Stenosis after Aortic Valve Replacement

ABSTRACT

BACKGROUND: The nature of depressed left ventricular ejection performance in chronic pressure-overload hypertrophy due to aortic stenosis is controversial. Patients with aortic stenosis and congestive heart failure who responded well and those who responded poorly to aortic valve replacement may represent two distinct groups, rather than opposite ends of a spectrum. Whereas excess afterload accompanied by inadequate hypertrophy of functioning cardiac muscle was been suggested as the cause of impaired left ventricular shortening, intrinsic depression of contractility of the hypertrophied myocardium was also been considered, at least in part, to be the cause of altered ejection performance. METHOD: We studied 20 patient with non-rheumatic aortic stenosis using echocardiogram and cineangiocardiography. The patients were divided into two groups according to the level of LVEF and New York Heart association [NYHA] functional class. In group 1, 7 patients had an echocardiographically determined LVEF less than 40% and clinical presentation of severe congestive heart failure(NYHA functional class III or IV). In group 2, 13 patients had LVEF more than 40% and NYHA functional class I or II. Left ventricular volumes and ejection fraction were determined from the echocardiogram obtained in short axis view. As a measure of left vertricular afterload, meridional end-systolic wall stress was calculated. This method is based on the determination of end-systolic left ventricular dimension, wall thickness and peak systolic pressure. RESULTS: 1) End-systolic meridional wall stress was significantly elevated in the patient with aortic stenosis & severe congestive heart failure(group 1) compared with the patient with aortic stenosis and mild congestive heart failure(group 2)(320.09+/-72.09 vs 177.52+/-76.43 dyne x 10(3)/cm2, p<0.005). With group 1 and group 2, there was a significant inverse linear relationship between LVEF and end systolic meridional wall stress(r=-0.907, p<0.001). 2) There was significantly more decreased ratio of end-systolic meridional wall stress to end-systolic volume index(ESWS/LVESVI) of group 1 than that of group 2(5.64+/-2.65 vs 15.30+/-7.77 dyne x 10(3)cm2/ml/m2, p<0.05). And there was a significant linear relationship between LVEF and end-systolic meridional wall stress to end-systolic volume index(ESWS/LVESVI)(r=0.86, p<0.001). 3) Twenty of 20(100%) survived after surgery : 19 of these 20 showed clinical improvement. There was significant improvement of ejection performance(LVEF, % FS) in group 1 except from 1 patient(LVEF 35.43+/-6.90 VS 47.29+/-3.45%, % FS 18.76+/-4.87 vs 28.20+/-3.40, p<0.05). CONCLUSION: Thus, both altered contractility and increased afterload are operative in depressed left vertricular ejection performance in patients wth aortic stenosis ; which one predominates may have major prognostic importance. We found encouraging results for aortic valve replacement in patient with depressed preoperative left ventricular function. The majorty of patients in this series had left ventricular failure because of excessive afterload predominantly.