ALTERATIONS IN LEFT-VENTRICULAR TWIST MECHANICS WITH INOTROPIC STIMULATION AND VOLUME LOADING IN HUMAN-SUBJECTS

Background Left ventricular (LV) twist, the longitudinal gradient of c ircumferential rotation about the LV long axis, may play an important role in the storage of potential energy at end systole and its subsequ ent release as elastic recoil during early diastole; however, the effe cts of load and inotropic state on LV systolic twist and diastolic unt wist in human subjects have not previously been characterized. Methods and Results Six cardiac transplant recipients with 12 implanted radio paque midwall LV myocardial markers were studied 1 year after transpla ntation. Biplane cinefluoroscopic marker images and LV pressure were r ecorded during control conditions and after afterload augmentation (me thoxamine, 5 to 10 mu g.kg(-1).min(-1)), inotropic stimulation (dobuta mine, 5 mu g.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 re lation (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 dopes (rad/cm) of the T-nEFR during early diastole (M(e ar-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 incr eased all parameters describing systolic twist (T-max: -0.10+/-0.03 ve rsus -0.06+/-0.02 rad/cm, P<.001; -dT/dt(min): -0.72+/-0.19 versus -0. 44+/-0.22 rad.cm(-1).s(-1), P<.001; M(sys): -0.10+/-0.03 versus -0.06/-0.01 rad/cm, P<.001). Pressure loading had no effect on early diasto lic untwisting; however, dobutamine significantly increased M(ear-dia) (-0.24+/-0.06 versus -0.13+/-0.04 rad/cm, P<.0001) and +dT/dt(max) (0 .78+/-0.24 versus 0.45+/-0.16 rad.cm(-1).s(-1), P<.001). Conversely, v olume loading significantly decreased M(ear-dia) (-0.08+/-0.04 versus -0.13+/-0.04 rad/cm, P<.05). M(ear-dia) correlated directly with LV co ntractile state (as assessed as maximum dP/dt, r=.60, P<.0001) and inv ersely with end-systolic volume (r=-.87, P<.0001) but was unrelated to stroke volume (r=.08, P=.30) or LV afterload (estimated as effective arterial elastance, r=.08, P=.29). M(mid-dia) did not change during an y intervention. Conclusions In conscious human transplant patients, (1 ) pressure and volume loading do not affect systolic LV twist; (2) dob utamine augments systolic twist and early diastolic untwisting, sugges ting more end-systolic potential energy storage and early diastolic el astic recoil with enhanced inotropic state; (3) volume loading decreas es early diastolic untwisting, possibly reflecting diminished recoil f orces after preload augmentation associated with larger end-systolic v olumes (ESV); and (4) M(ear-dia) correlates strongly with ESV (in an i nverse fashion), and less strongly, but directly, with LV dP/dt(max). 1993;89:142-150.)