Assessment of left ventricular relaxation by Doppler echocardiography. Comparison of isovolumic relaxation time and transmitral flow velocities with time constant of isovolumic relaxation.

Isovolumic relaxation time (IVRT) and events of early transmitral flow measured by Doppler echocardiography were validated against the time constant of left ventricular relaxation (tau) in open-chest dogs. During increased inotropy (by isoproterenol infusion) at constant preload, enhancement of relaxation was indicated by a decrease in tau from 48 +/- 12 (mean +/- SD) to 33 +/- 5 msec (p = 0.04) with a concomitant decrease in IVRT from 74 +/- 18 to 38 +/- 8 msec (p = 0.03). During decreased inotropy (by propranolol infusion) at constant preload, slowing of relaxation was indicated by an increase in tau from 40 +/- 8 to 51 +/- 13 msec (p = 0.02) with a concomitant increase in IVRT from 71 +/- 15 to 83 +/- 21 msec (p less than 0.05). A significant correlation between changes in tau and changes in IVRT was found (r = 0.66, p less than 0.001). In contrast, when left ventricular end-diastolic pressure was increased from 7 +/- 2 to 24 +/- 4 mm Hg at constant inotropy, tau increased from 47 +/- 14 to 64 +/- 25 msec (p = 0.03), whereas no change in IVRT was observed (76 +/- 19 and 71 +/- 19 msec, respectively). Aortic pressure was not significantly changed during any intervention, and heart rate was kept constant by pacing. Peak early transmitral velocity was unchanged by propranolol but increased during isoproterenol and saline infusion (p less than 0.001 and p less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)