An Echophonocardiographic Study on Left Ventricular Isovolumic Relaxation Time

ABSTRACT

Cardiac relaxation is impaired in many cardiac disorders and is the subject of extensive investigation. Though measurement of isovolumic relaxation time ought to prove a simple means of quantifying such abnormalities in clinical practice, the problem of defining the timing of mitral valve opening at the onset of ventricular filling has been a difficulty. previous studies have used the 'O' point of the apexcardiogram, but more recently it has been shown that this may be open to considerable error. It was the purpose of the present study to determine the duration of true isovolumic relaxation and the factors influencing its duration, and to evaluate its use as a simple noninvasive measurement of cardiac dynamics in terms of the present approach. True isovolumic relaxation time (IRT) was measured noninvasively from the onset of the aortic component of the second heart sound to the onset of rapid opening of the mitral leaflets from simultaneous recording of echocardiogram, phonocardiogram, electrocardiogram and carotid tracing in 60 normal subjects, 30 male and 30 female and in 50 with hypertension, 28 male and 22 female ranging in age from 20 to 45 years. 1. The duration of IRT was 53.6+/-9.9 msec in normal subjects with no relation to sex. 2. IRT was related to heart rate, systemic blood pressure, and systolic and diastolic time intervals. 1) IRT tended to decrease with increasing heart rate and a regression equation for predicting it in relation to heart rate was 'IRT(msec)=88.97-0.466xH.R.(beats/min)' (P<0.01). 2) IRT tended to increase with increasing systemic blood pressure and a regression equation for predicting it in relation to aortic closing pressure was 'IRT(msec)=5.09+0.459xaortic closing pressure(mmHg)' (P<0.01). IRT was prolonged in patient with hypertension. 3) IRT was in close relation to left ventricular contraction indices such as preejection period(PEP), isovolumic contraction time and preejection period/left ventricular ejection time ratio. 4) There was no relation between IRT and left ventricular pump performance indices such as stroke volume, ejection fraction, fractional shortening and left ventricular dimension. 5) There was strong association between IRT and diastolic time intervals. Authors were impressed through this study that IRT is a useful measurement of left ventricular dynamics in early diastole.