LEFT-VENTRICULAR FUNCTION, TWIST, AND RECOIL AFTER MITRAL-VALVE REPLACEMENT

Background Preservation of the mitral subvalvular apparatus during mit ral valve replacement (MVR) has become more popular, in part because o f the clinically and experimentally demonstrated more optimal left ven tricular (LV) performance after surgery; the mechanisms responsible fo r this beneficial influence, however, have not been clearly elucidated . Methods and Results Fourteen dogs underwent placement of 26 myocardi al markers into the LV and septum. One week later, the animals were st udied while awake, sedated, and atrially paced (120 beats per minute) both under baseline conditions and after inotropic stimulation (calciu m). The animals then underwent MVR and were randomized into either cho rd-sparing (MVR-Intact) or chord-severing (MVR-Cut) techniques. Two we eks later, the animals were studied under the same conditions. LV syst olic function was assessed by the slope of the end-systolic pressure-v olume relation (E(es)); early LV diastolic filling was analyzed by the pressure-time constant of relaxation (tau). The instantaneous longitu dinal gradient of torsional deformation for the LV (twist) was also ca lculated, as were the changes in twist with respect to time during sys tole and early diastole (LV recoil). Intergroup comparison showed a tr end toward increased contractility (E(es), P=.061, before versus after MVR), as well as faster relaxation for the MVR-Intact group. Concurre nt analysis of LV systolic function and the rate of systolic twist rev ealed a significant inverse relation, which disappeared after MVR when the chordae were severed. Conclusions These observations suggest that the mitral subvalvular apparatus acts as a modulator of LV systolic t orsional deformation into LV pump (or ejection) performance.