Ventricular untwisting: a temporal link between left ventricular relaxation and suction
American Journal of Physiology. Heart and Circulatory Physiology
Left ventricular (LV) untwisting starts early during the isovolumic relaxation phase and proceeds throughout the early filling phase, releasing elastic energy stored by the preceding systolic deformation. Data relating untwisting, relaxation, and intraventricular pressure gradients (IVPG), which represent another manifestation of elastic recoil, are sparse. To understand the interaction between LV mechanics and inflow during early diastole, Doppler tissue images (DTI), catheter-derived
... (apical and basal LV, left atrial, and aortic), and LV volume data were obtained at baseline, during varying pacing modes, and during dobutamine and esmolol infusion in seven closed-chest anesthetized dogs. LV torsion and torsional rate profiles were analyzed from DTI data sets (apical and basal short-axis images) with high temporal resolution (6.5 Ϯ 0.7 ms). Repeated-measures regression models showed moderately strong correlation of peak LV twisting with peak LV untwisting rate (r ϭ 0.74), as well as correlations of peak LV untwisting rate with the time constant of LV pressure decay (tau, r ϭ Ϫ0.66) and IVPG (r ϭ 0.76, P Ͻ 0.0001 for all). In a multivariate analysis, peak LV untwisting rate was an independent predictor of tau and IVPG (P Ͻ 0.0001, for both). The start of LV untwisting coincided with the beginning of relaxation and preceded suction-aided filling resulting from elastic recoil. Untwisting rate may be a useful marker of diastolic function or even serve as a therapeutic target for improving diastolic function. diastole; relaxation; suction; torsion EARLY DIASTOLE, which we define here as a period encompassing isovolumic pressure decay and rapid left ventricular (LV) filling, is characterized by a series of consecutive events that partially overlap in time. As LV pressure starts to decline before mitral valve opening, conformational changes occur within the heart that are reflective of the release of energy stored during previous systole (19) . Mitral valve opening is immediately followed with the development of intraventricular pressure gradient (IVPG), a difference between high-and low-pressure fields in the LV base and apex (8). Finally, LV inflow is accelerated by IVPG to reach peak filling velocity (18). It is widely accepted that appearance of IVPG in early diastole reflects LV suction (20), i.e., low pressure field created by outward-directed elastic forces that aim to restore a nonstressed LV shape (19) . It is also accepted that IVPG facilitates early LV filling (16). LV systolic torsional (twisting) deformation is one mechanism by which potential energy is stored during ejection, to be later released during diastole and contribute to the creation of suction.