Comparison of Left Ventricular Myocardial Structure and Function in Patients with Aortic Stenosis and Those with Pure Aortic Regurgitation

Objective: We aimed to support the structural and functional distinction between aortic stenosis (AS) and aortic regurgitation (AR). Methods: Biopsy specimens taken from 70 selected patients (35 with AS and 35 with AR) undergoing aortic valve replacement (AVR) were analyzed for their cardiomyocyte dimensions and structure, interstitial fibrosis and contractile function. To determine normal values of contractile function, 10 donor hearts were analyzed. Results: Cardiomyocyte diameter was higher in AS than in AR (22.7 ± 2.2 vs. 13.2 ± 0.7 µm, p < 0.001). Length was higher in AR (121.2 ± 9.4 vs. 95.6 ± 3.7 µm, p < 0.001). Collagen volume fraction was increased in both AS and AR, but was lower in the AS specimens (7.7 ± 2.3 vs. 8.9 ± 2.3, p = 0.01). Myofibril density was reduced in AR (38 ± 4 vs. 48 ± 5%, p < 0.001). Cardiomyocyte diameter and length were closely linked to the relative left ventricular (LV) wall thickness (R 2 = 0.85, p < 0.001 and R 2 = 0.68, p = 0.003). The cardiomyocytes of AS patients had higher F passive (6.6 ± 0.3 vs. 4.6 ± 0.2 kN/m 2 , p < 0.001), but their total force was comparable. F passive was also significantly higher in AS patients with restrictive rather than pseudo-normal LV filling (7.3 ± 0.5 vs. 6.7 ± 0.6, p = 0.004). In AS patients, but not in AR patients, F passive showed a significant association with the cardiomyocyte diameter (R 2 = 0.88, p < 0.001 vs. R 2 = 0.31, p = 0.6). Conclusions: LV myocardial structure and function differ in AS and AR, allowing for compensative adjustment of the diastolic/systolic properties of the myocardium.