January 7, 1997
View Full PaperNoninvasive Assessment of the Ventricular Relaxation Time Constant (τ) in Humans by Doppler Echocardiography
Structured PICO
Does noninvasive assessment using Doppler echocardiography accurately predict the invasive ventricular relaxation time constant (tau) in patients undergoing cardiac surgery?
P
Population
11 patients undergoing cardiac surgery
I
Intervention
Noninvasive assessment of ventricular relaxation time constant (tau Dopp) using Doppler echocardiography and clinical parameters (peak systolic blood pressure, mean left atrial pressure, and Doppler-derived isovolumic relaxation time)
C
Comparator
Invasive measurement of tau (tau LM) via high-fidelity left atrial and left ventricular pressure recordings (gold standard)
O
Outcome
Correlation between noninvasive tau Dopp and invasive tau LMsurrogate
A noninvasive method using Doppler echocardiography and clinical blood pressures can closely predict the ventricular relaxation time constant (tau), providing a practical tool for assessing diastolic function.
Abstract
BACKGROUND: The time constant of ventricular relaxation (tau) is a quantitative measure of diastolic performance requiring intraventricular pressure recording. This study validates in humans an equation relating tau to left ventricular pressure at peak -dP/dt (P0), pressure at mitral valve opening (PMV), and isovolumic relaxation time (IVRTinv). The clinically obtainable parameters peak systolic blood pressure (Ps), mean left atrial pressure (PLA), and Doppler-derived IVRT (IVRTDopp) are then substituted into this equation to obtain tau 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 tau LM, the "gold standard" against which tau calc (IVRT inv/ln(P0)-ln(PMV)) and tau Dopp IVRTDopp/[ln(Ps)-ln(PLA)] were compared. For 123 cycles analyzed in 18 hemodynamic states, mean tau LM was 53.8 +/- 12.9 ms. tau calc (51.5 +/- 11 ms) correlated closely with this standard (r = .87, SEE = 5.5 ms). Noninvasive tau Dopp (43.8 +/- 11 ms) underestimated tau LM but exhibited close linear correlation (n = 88, r = .75, SEE = 7.5 ms). Substituting PLA = 10 mm Hg into the equation yielded tau 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 tau is valid in humans. Furthermore, a more clinically obtainable, noninvasive method of obtaining tau also closely predicts this important measure of diastolic function.