Measurement of isovolumic relaxation: comparison of echocardiographic mitral valve opening and Doppler mitral valve flow

The relation between mitral valve opening and transmitral blood flow was investigated by M-mode echocardiography and Doppler ultrasound in 50 normal subjects to allow the measurement of the timing of the end of isovolumic relaxation. Standard parasternal M-mode echocardiograms of the mitral valve to show the onset of cusp separation were recorded with a simultaneous electrocardiogram and phonocardiogram. Pulse wave Doppler ultrasound using both amplitude and spectral analysis was recorded with a transducer at the apex, and the initial diastolic blood flow towards the transducer was taken as the onset of flow. For each subject five cardiac cycles of similar length were measured using the three methods. Isovolumic relaxation could be measured with a high degree of reliability (retest reliability coefficient greater than 0.94). The echocardiographic measurement of isovolumic relaxation ranged from 52 to 82 ms (mean(SD) 67(9) ms). Isovolumic relaxation measured by Doppler was 52-83 ms (mean(SD) 67(9) ms) using amplitude analysis and 54-89 ms (mean(SD) 72(11) ms) using spectral analysis. There was a strong correlation between the echocardiographic isovolumic relaxation and measurements made using spectral analysis (r = 0.93, slope 0.97) and amplitude analysis (r = 0.97, slope 0.98). Therefore in normal subjects the end of isovolumic relaxation can be reliably measured by echocardiographic and Doppler methods, and whereas the amplitude signal is coincidental with that measured by echocardiography that measured by spectral analysis is delayed by approximately 5 ms.