VENTRICULAR PERFORMANCE Left ventricular filling dynamics : influence of left ventricular relaxation and left atrial pressure

Peak rapid filling rate (PRFR) is often used clinically as an index of left ventricular relaxation, i.e., of early diastolic function. This study tests the hypothesis that early filling rate is a function of the atrioventricular pressure difference and hence is influenced by the left atrial pressure as well as by the rate of left ventricular relaxation. As indexes, we chose the left atrial pressure at the atrioventricular pressure crossover (PCO), and the time constant (T) of an assumed exponential decline in left ventricular pressure. We accurately determined the magnitude and timing of filling parameters in conscious dogs by direct measurement of phasic mitral flow (electromagnetically) and high-fidelity chamber pressures. To obtain a diverse hemodynamic data base, loading conditions were changed by infusions of volume and angiotensin LI. The latter was administered to produce a change in left ventricular pressure of less than 35% (A-1) or a change in peak left ventricular pressure of greater than 35% (A-2). PRFR increased with volume loading, was unchanged with A-1, and was decreased with A-2; T and PCO increased in all three groups (p < .005 for all changes). PRFR correlated strongly with the diastolic atrioventricular pressure difference at the time of PRFR (r = .899, p < .001) and weakly with both T (r = .369, p < .01) and PCO (r = .601, p < .001). The correlation improved significantly when T and PCO were both included in the multivariate regression (r = .797, p < .0001). PRFR is thus determined by both the left atrial pressure and the left ventricular relaxation rate and should be used with caution as an index of left ventricular diastolic function. Circulation 74, No. 1, 187-196, 1986. RELAXATION ABNORMALITIES are one of the earliest manifestations of cardiac dysfunction and frequently precede systolic dysfunction in many disease states.'' Early filling function has been evaluated in a variety of diseases, e.g., coronary artery disease, hypertrophic cardiomyopathy, hypertensive heart disease, aortic valve disease, and congestive cardiomyopathy.'6 Since its introduction by Weiss et al.,17 the time constant (T) of an assumed exponential isovolumetric pressure decline has been accepted as a good indicator of early cardiac function and is now frequently measured during cardiac catheterization to evaluate left ventricular relaxation.3' 4, 7, 12, 14 Because this direct index of isovolumetric relaxation requires an invasive measurement of left ventricular pressure, many investigators assume that left ventricular relaxation can be From the Departments of Surgery, Physiology and Biophysics, and Medicine, Albert Einstein College of Medicine, Bronx, NY. Supported in part by the National Institutes of Health under research grants HL 24638, HL 19319, and T32 GM 7288 from the NIGMS. Address for correspondence: Edward L. Yellin, Ph.D., Department of Surgery, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461. Received Aug. 27, 1985; revision accepted April 10, 1986. Vol. 74, No. 1, July 1986 assessed indirectly by estimating early diastolic filling. For example, peak rapid filling rate (PRFR) has been derived from radionuclide angiography, 10 11, 16 peak rates of chamber or wall dimension change have been measured from M mode echocardiograms ,6, 9 15 and peak rapid filling velocity has been determined with Doppler ultrasound.'3 These approaches are based on the principle that the falling ventricular pressure contributes to the generation of the atrioventricular pressure difference that accelerates the blood across the mitral valve. Fioretti et al.7 and Magorien et al.'6 have shown a statistically significant, but weak, correlation between the time constant of relaxation and the rapid filling rate. Further clarification of the physiology of transmitral blood flow, based on invasive animal experiments, would be helpful in the interpretation of data obtained by noninvasive means in the clinical setting. We have shown that the transmitral pressure-flow relationship can be described qualitatively by the following equation of motion: AP = (A)d(MiF)/dt + (B)(MiF) 187 by gest on N ovem er 7, 2017 http://ciajournals.org/ D ow nladed from