Noninvasive Assessment of Left Ventricular Force-Frequency Relationships Using Tissue Doppler–Derived Isovolumic Acceleration

Abstract

Background— We have demonstrated that myocardial acceleration during isovolumic contraction (IVA) is a sensitive index of right ventricular contractile function. In this study, we assessed the usefulness of IVA to measure left ventricular (LV) contractile function and force-frequency relationships in an experimental preparation. Methods and Results— In study 1, we examined 6 pigs by use of tissue Doppler imaging of LV free wall and simultaneous measurements of intraventricular pressure, volume, maximal elastance (E max ), and dP/dt max by conductance catheterization. Animals were paced via the right atrium at a rate of 130 bpm. IVA was compared with elastance during contractility modulation by esmolol and dobutamine and assessed during preload reduction and afterload increase. In study 2, in 6 more pigs, force-frequency data were obtained during incremental atrial pacing from 120 to 180 bpm. Study 1: Esmolol led to a decrease in IVA and E max ( P <0.03 and <0.02, respectively), both of which increased during dobutamine infusion ( P <0.02 and <0.03, respectively). IVA was unaffected by significant ( P <0.001) acute reduction of LV volume and a significantly increased LV afterload (systolic pressure increase, P <0.001). Study 2: There was a positive correlation between IVA and dP/dt max ( r 2 =0.92, P <0.05). As heart rate was increased from 120 to 160 bpm, there were significant increases in both IVA and dP/dt max ( P <0.0004 and P =0.02, respectively). Over the same range of heart rates, there was no significant change in E max ( P =0.22). Conclusions— IVA is a measurement of LV contractile function that is unaffected by preload and afterload changes within a physiological range and can be used noninvasively to measure LV force-frequency relationships.