Aortic acceleration as noninvasive index of left ventricular contractility

Abstract

Background: Left ventricular (LV) contractility is assessed with the invasively measured LV pressure derivative (+dP/dtmax), which is a terminal procedure in mice and other similar sized animals. Noninvasive methods to assess LV contractility have been reported in patients, sheep, dogs, and rats. We undertook this study to validate the use of acceleration of aortic flow velocity in lieu of +dP/dtmax to assess LV contractility in mice. Methods: We measured aortic blood flow velocity noninvasively simultaneous with invasive measurement of LV pressure in the anesthetized mouse. Mean, Ym (=Vp/Tp) and peak, Yp (=dV/dtmax) aortic accelerations were calculated and compared to +dP/dtmax (X) calculated from LV pressure. Measurements were made at baseline and post-dobutamine administration (1μg/g BW) in 4 wild type male mice (C57BL6/J). Results: Peak and mean aortic accelerations were compared to +dP/dtmax at several heart rates (range: 387 to 701 bpm, n=18 data points). Linear regression of both, peak aortic acceleration (Yp) versus +dP/dtmax (X) and mean aortic acceleration (Ym) versus +dP/dtmax (X), showed a high correlation - (Yp = 2.8X + 1617; p<0.0001; r2 = 0.896) and (Ym = 1.4X + 1319; p<0.0001; r2 = 0.903), respectively. Conclusion: The high correlation between Yp versus +dP/dtmax is in agreement with that reported in dogs, while that between Ym versus +dP/dtmax is similar to that reported in sheep. Mean acceleration requires measurement of time (Tp) to peak velocity (Vp) which can be difficult at times due to the ambiguity in the location of the peak velocity. Peak aortic acceleration is much easier to measure using the first derivative and is also highly correlated with +dP/dtmax. Preliminary result of this study suggest that both peak and mean aortic acceleration may be used as a noninvasive index of LV contractility in mice. We expect to evaluate these relationships further under various loading conditions.