Abstract:

OBJECTIVES:The present study aimed at investigating the respective contribution of afterload and myocardial fibrosis to pre- and post-operative left ventricular (LV) function by using stress-strain relationships. BACKGROUND:Separating the effect of myocardial dysfunction and afterload on pump performance has important implications for the prognosis and management of patients with severe aortic stenosis (AS). METHODS:A total of 101 patients with isolated severe AS (57% men; mean age 71 years) and 75 healthy control subjects underwent resting 2-dimensional and speckle-tracking echocardiography to measure global circumferential strain (GCS) and global longitudinal strain (GLS), as well as end-systolic wall stress (ESWS). Normal stress-strain relationships were constructed using control subjects' data and fitted to linear regression. End-systolic stress-strain indexes (the number of SDs from the mean regression line) were used as an afterload-independent index of myocardial function and compared with myocardial fibrosis, measured on transmural myocardial biopsies harvested at the time of surgery. RESULTS:GCS and GLS were afterload-dependent in both control subjects and patients. The GLS-ESWS relationship of patients was shifted downward compared with control subjects. Patients with reduced pre-operative end-systolic stress-strain indexes exhibited larger degrees of interstitial myocardial fibrosis than patients without (3.8 ± 2.9% vs. 8.3 ± 6.3%, p < 0.001; and 4.9 ± 4.4% vs. 9.5 ± 6.4%; p < 0.001, for GLS and GCS, respectively). By multivariate analysis, pre-operative end-systolic stress-strain indexes were the only predictors of post-operative longitudinal and circumferential end-systolic stress-strain indexes (ß = 0.49 and ß = 0.60, respectively; p < 0.001). CONCLUSIONS:Myocardial strains are afterload-dependent. In patients with severe AS, pre-operative stress-strain indexes allow identification of patients with increased myocardial fibrosis and predict the extent of functional recovery after aortic valve replacement.