Diastolic left ventricular pressure-volume and stress-strain relations in patients with valvular aortic stenosis and left ventricular hypertrophy

Abstract

Left ventricular (LV) chamber and myocardial stiffness were determined in 17 patients, 4 subjects with normal LV function and 13 subjects with valvular aortic stenosis and concentric myocardial hypertrophy, using simultaneous catheter micromanometry and LV cineangiography. Pressure (P), volume (V), and wall thickness (h) were measured. Variability in both chamber and myocardial stiffness parameters was found with 5 of the aortic stenosis patients (Group 1, left ventricular end diastolic pressure = 15 ± 2 (SEM) mm Hg) exhibiting normal values for end diastolic dP/dV and dP/dV/V, for chamber stiffness constants (a, a') derived from P-V and normalized P-V relations, respectively, for end diastolic myocardial elastic stiffness (E(S) or E(E), where S = spherical model and E = ellipsoidal model) at the midwall of the minor axis circumference, and for the myocardial stiffness constants (K(S) or K(E)) of the circumferential stress strain relation. Eight other patients with aortic stenosis (Group II, left ventricular end diastolic pressure = 20 ± 3 (SEM) mm Hg) exhibited significant increases in end diastolic dP/dV, dP/dV/V, E(S) and E(E) and a tendency for increase in the chamber stiffness constants (a, a') and myocardial stiffness constants (K(S), K(E)). These observations suggest that concentric increase in muscle mass (increase in wall thickness/minor axis radius ratio and wall volume/chamber volume ratio) is an important determinant of elevated mid and late diastolic pressures in patients with valvular aortic stenosis, while concurrently mitigating increases in both systolic and diastolic wall stress. In some patients with aortic stenosis, however, diastolic filling pressures are elevated more severely, not only as a result of concentric hypertrophy, but also in response to augmented muscle stiffness. Reversibility of increased ventricular diastolic stiffness and elevated filling pressures was documented as concentric hypertrophy regressed post-aortic valve replacement in one patient, suggesting that fibrosis is not invariably the cause of enhanced myocardial stiffness in this secondary and compensatory form of hypertrophy.