Ventricular relaxation and myocardial ischemia: A comparison of different models of tau during coronary angioplasty

This study compares the sensitivity and variability of four models of tau, the time constant of ventricular relaxation, to detect the presence of myocardial ischemia. High fidelity left ventricular pressure recordings were obtained in ten patients undergoing coronary angioplasty at baseline, during balloon inflation, and at recovery. Four models of tau were considered: 1) a semilogarithmic, zero asymptote model (TL), 2) a semilogarithmic model using data from the first 40 ms of isovolumic relaxation (T40), 3) an exponential non-zero asymptote model (TE), and 4) a derivative non-zero asymptote model (TD). TL, T40, and TE increased significantly during inflation and returned to near baseline values at recovery. TD showed no change during inflation. Comparisons of TL, T40, and TE using the derived relaxation half-time (T1/2), failed to reveal significant differences between the models at baseline, during inflation, or at recovery. The non-zero asymptote models were associated with a greater beat-to-beat variability than the semilogarithmic models. Thus, T1/2 using the semilogarithmic zero asymptote models (TL and T40) may be more useful and consistent when measuring the rate of isovolumic relaxation during myocardial ischemia.