Left ventricular myocardial stiffness

Abstract

Left ventricular (LV) myocardial stiffness (kS) is an index of muscle properties independent of chamber geometry and is important in understanding normal and abnormal physiology, but is difficult to measure in vivo. Defining the LV as a thick-walled prolate sphere with minor radius R, accepted definitions of stress (σ) and natural strain were used to show the σ- R relation is a power function, and kS relates to the curvature by σ = C1 + C2 RkS. Importantly, this derivation avoids constraints on the σ- R relation and the need for LV dimensions at σ = 0. This model was then applied in humans and in dogs with intact pericardium. LV pressure and volume are lowered by nifedipine; in 32 patients kS was unchanged and thus peripheral effects implicated. Ejection fraction (EF) decreases with coronary occlusion and improves with early reperfusion. This could represent salvage of muscle or further damage with increased kS and resultant decrease of muscle bulging. In 20 dogs it was shown that kS increases with coronary occlusion and that early reperfusion causes kS to improve at the same time as EF. This implies salvage with major clinical implications.