[Which time constant of left ventricular relaxation is the most sensitive measure in acute myocardial ischemia?]

To investigate which time constant of isovolumic left ventricular pressure (LVP) decay is the most sensitive measure in acute myocardial ischemia, the time constant of isovolumic relaxation (IR) was calculated by two different models, the semilogarithmic model assuming a zero of LVP decline (TL) and an exponential model (Texp) with an asymptote (extrapolated baseline pressure to which LVP would fall if decay continued indefinitely), in 10 patients before and during ergonovine-induced vasospastic angina. Two time constants were derived from the exponential method as the times for LVP at peak negative dP/dt to decline by 1/e (Texp (1/e)) and by one half (Texp (1/2)). Three changes in LVP during isovolumic relaxation were analyzed and fitted to the two models described above: the LVP from the peak negative dP/dt 1) to when LVP fell to 5 mmHg above LV end-diastolic pressure (EDP), 2) until 40 msec had passed, and 3) to the LVP level 5 mmHg above LVEDP during coronary spasm. There were significant increases in TL, Texp (1/e) and Texp (1/2) in each period of the LVP during vasospastic angina. However, no significant change in Texp or asymptote was observed during angina. We concluded that TL measured by the semilogarithmic model assuming a zero of LVP decline and Texp (1/e) or Texp (1/2) derived from the exponential model are adequately sensitive for detecting acute myocardial ischemia due to coronary spasm.