Non-invasive determination of left ventricular relaxation time constant by transthoracic Doppler echocardiography

Background. Left ventricular (LV) relaxation time constant (Tau) is a relatively load-independent index of diastolic function in the evaluation of heart failure. However, the requirement of high-fidelity intraventricular pressure recording limits its clinical utility. In the present study, we investigated whether Tau could be estimated noninvasively. Methods. Thirty-seven patients indicated for cardiac catheterization were recruited for study. Echocardiography and cardiac catheterization with high-fidelity LV pressue recording were performed sequentially within 1 hour. The non-invasive Taud,_Dopp was derived from the formula: Tau_Dopp = IVRT_Dopp/ [ln(Ps) - ln(10)], where IVRT is the isovolumic relaxation time measured by Doppler echocardiography and Ps is systolic blood pressure measured during the echocardiographic examination. The invasive Tau_LM was determined by non-linear least-square parameter estimate technique, using the exponential equation: Pv = P₀e^-t/Tau + b, where Pv is the instantaneous LV pressure, P₀ is LV pressure at minimal dP/dt, and b is the theoretical asymptote. The difference between Tau_Dopp and Tau_LM was compared using paired t-test, and their relation was evaluated using simple correlation and intra-class correlation coefficient. Results. IVRT_Dopp was significantly correlated with the invasively derived IVRT (r = 0.42, p = 0.012). The completely non-invasive Tau_Dopp was significantly correlated with the direct curve-fitted Tau_LM (r = 0.41; p = 0.013), and the intraclass correlation coefficient was 0.29 (p 0.04). In addition, Tau_Dopp was significantly smaller than TaU_LM (36 ± 6 ms vs. 57 ± 15 ms,p < 0.001). Conclusions. Tau can be estimated noninvasively by transthoracic Doppler echocardiographic method with limited accuracy. The clinical utility of Tau_Dopp remains to be determined.