Alterations in left ventricular twist mechanics with inotropic stimulation and volume loading in human subjects

Abstract

Background: Left ventricular (LV) twist, the longitudinal gradient of circumferential rotation about the LV long axis, may play an important role in the storage of potential energy at end systole and its subsequent release as elastic recoil during early diastole; however, the effects of load and inotropic state on LV systolic twist and diastolic untwist in human subjects have not previously been characterized. Methods and Results: Six cardiac transplant recipients with 12 implanted radiopaque midwall LV myocardial markers were studied 1 year after transplantation. Biplane cinefluoroscopic marker images and LV pressure were recorded during control conditions and after afterload augmentation (methoxamine, 5 to 10 μg · kg-1 · min-1), inotropic stimulation (dobutamine, 5 μg · kg-1 · min-1), and preload augmentation (volume loading with normal saline). Systolic twist dynamics were assessed by maximum twist (T(max)[rad/cm]), peak negative twist rate (-dT/dt(min)[rad · cm-1 · s-1]), and the slope of the twist normalized-ejection fraction relation (T-nEFR, M(sys)[rad/cm]) during systole. Diastolic untwist was assessed by the peak positive untwist rate (+dT/dt(max) [rad · cm-1 · s-1]) and the slopes (rad/cm) of the T-nEFR during early diastole (M(ear-dia)) and mid diastole (M(mid-dia)). Compared with control values, LV pressure and volume loading had no significant effect on T(max), -dT/dt(min), or M(sys); however, inotropic stimulation significantly increased all parameters describing systolic twist (T(max); - 0.10±0.03 versus -0.06±0.02 rad/cm, P