Continuous wave Doppler echocardiography for noninvasive assessment of left ventricular dP/dt and relaxation time constant from mitral regurgitant spectra in patients

Objectives. We previously demonstrated experimentally that the mitral regurgitant velocity spectrum can be used to estimate left ventricular pressure throughout systole and may provide a new noninvasive method for estimating maximal dP/dt and the relaxation time constant. This study was designed to test this method in patients. Background. The maximal first derivative of left ventricular pressure (dP/dt) and the time constant of left ventricular isovolumetric relaxation (τ) are important variables of left ventricular function, but the need for invasive measurement with high fidelity catheters has limited their use in clinical cardiology. Methods. Twelve patients with mitral regurgitation were studied. The Doppler mitral regurgitant velocity spectrum was recorded simultaneously with micromanometer left ventricular pressure tracings in all patients. The regurgitant velocity profiles were digitized and converted to ventriculoatrial (VA) pressure gradient curves using the simplified Bernoulli equation and differentiated into instantaneous dP/dt. The relaxation time constant (τ) was calculated assuming a zero pressure asymptote from catheter left ventricular pressure decay (τ_c) and forn the Dopplerderived VA gradient curve with corrections. Two methods were used to correct the Doppler gradient curve to better approximate the left ventricular pressure decay before calculating the relaxation time constant: 1) adding an arbitrary 10 mm Hg (τ₁₀), and 2) adding the actual mean pulmonary capillary pressure (τ_la). Results. The Doppler-derived maximal positive dP/dt (1,394 ± 302 mm Hg/s [mean ± SD]) correlated well (r = 0.91) with the catheter-derived maximal dP/dt (1,449 ± 307 mm Hg/s). Although the Doppler-derived negative maximal dP/dt differed slightly from catheter measurement (1,014 ± 289 vs. 1,195 ± 354 mm Hg/s, p < 0.01), the correlation between Doppler and catheter measurements was similarly good (r = 0.89, p < 0.0001). The correlation between τ₁₀ and τ_c was excellent (r = 0.93, p < 0.01), but the Doppler-derived τ₁₀ (50.0 ± 11.0 ms) slightly underestimated the catheter-derived τ_c (55.5 ± 12.8 ms, p < 0.01). This slight underestimation could be corrected by adding the actual pulmonary capillary wedge pressure to the Doppler gradient curve. Conclusions. Doppler echocardiography provides an accurate and reliable method for estimating left ventricular maximal positive dP/dt, maximal negative dP/dt and the relaxation time constant (τ) in patients with mitral regurgitation.