Noninvasive Assessment of the Ventricular Relaxation Time Constant (τ) in Humans by Doppler Echocardiography

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Abstract
Background The time constant of ventricular relaxation (τ) is a quantitative measure of diastolic performance requiring intraventricular pressure recording. This study validates in humans an equation relating τ to left ventricular pressure at peak −dP/dt (P 0 ), pressure at mitral valve opening (P MV ), and isovolumic relaxation time (IVRT inv ). The clinically obtainable parameters peak systolic blood pressure (P s ), mean left atrial pressure (P LA ), and Doppler-derived IVRT (IVRT Dopp ) are then substituted into this equation to obtain τ Dopp noninvasively. Methods and Results High-fidelity left atrial and left ventricular pressure recordings with simultaneous Doppler by transesophageal echocardiography were obtained from 11 patients during cardiac surgery. Direct curve fitting to the left ventricular pressure trace by Levenberg-Marquardt regression assuming a zero asymptote generated τ LM , the “gold standard” against which τ calc {IVRT inv /[ln(P 0 )−ln(P MV )]} and τ Dopp {IVRT Dopp /[ln(P s )−ln(P LA )]} were compared. For 123 cycles analyzed in 18 hemodynamic states, mean τ LM was 53.8±12.9 ms. τ calc (51.5±11 ms) correlated closely with this standard ( r =.87, SEE=5.5 ms). Noninvasive τ Dopp (43.8±11 ms) underestimated τ LM but exhibited close linear correlation (n=88, r =.75, SEE=7.5 ms). Substituting P LA =10 mm Hg into the equation yielded τ 10 (48.7±15 ms), which also closely correlated with the standard ( r =.62, SEE=11.6 ms). Conclusions The previously obtained analytical expression relating IVRT, invasive pressures, and τ is valid in humans. Furthermore, a more clinically obtainable, noninvasive method of obtaining τ also closely predicts this important measure of diastolic function.