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CLINICAL STUDY: CARDIAC PHYSIOLOGY

Noninvasive estimation of transmitral pressure drop across the normal mitral valve in humans: importance of convective and inertial forces during left ventricular filling

^a Cardiovascular Imaging Center, Department of Cardiology, Cleveland, Ohio, USA
^b Department of Thoracic and Cardiovascular Surgery, Cleveland Clinic Foundation, Cleveland, Ohio, USA

Manuscript received February 23, 2000; revised manuscript received June 1, 2000, accepted July 25, 2000.

Reprint requests and correspondence: Dr. James D. Thomas, Department of Cardiology, Desk F-15, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195
thomasj{at}ccf.org

OBJECTIVES

We hypothesized that color M-mode (CMM) images could be used to solve the Euler equation, yielding regional pressure gradients along the scanline, which could then be integrated to yield the unsteady Bernoulli equation and estimate noninvasively both the convective and inertial components of the transmitral pressure difference.

BACKGROUND

Pulsed and continuous wave Doppler velocity measurements are routinely used clinically to assess severity of stenotic and regurgitant valves. However, only the convective component of the pressure gradient is measured, thereby neglecting the contribution of inertial forces, which may be significant, particularly for nonstenotic valves. Color M-mode provides a spatiotemporal representation of flow across the mitral valve.

METHODS

In eight patients undergoing coronary artery bypass grafting, high-fidelity left atrial and ventricular pressure measurements were obtained synchronously with transmitral CMM digital recordings. The instantaneous diastolic transmitral pressure difference was computed from the M-mode spatiotemporal velocity distribution using the unsteady flow form of the Bernoulli equation and was compared to the catheter measurements.

RESULTS

From 56 beats in 16 hemodynamic stages, inclusion of the inertial term ([p_I]_max = 1.78 ± 1.30 mm Hg) in the noninvasive pressure difference calculation significantly increased the temporal correlation with catheter-based measurement (r = 0.35 ± 0.24 vs. 0.81 ± 0.15, p < 0.0001). It also allowed an accurate approximation of the peak pressure difference ([p_C+I]_max = 0.95 [p_cath]_max + 0.24, r = 0.96, p < 0.001, error = 0.08 ± 0.54 mm Hg).

CONCLUSIONS

Inertial forces are significant components of the maximal pressure drop across the normal mitral valve. These can be accurately estimated noninvasively using CMM recordings of transmitral flow, which should improve the understanding of diastolic filling and function of the heart.

Abbreviations and Acronyms   v/t = partial derivative of velocity with respect to time   v/s = partial derivative of velocity with respect to space (LA to LV)   p/s = partial derivative of pressure with respect to space   pcath = instantaneous transmitral pressure difference based on catheter measurement   pC = convective component of the instantaneous transmitral pressure difference (using the simplified Bernoulli equation)   pI = inertial component of the instantaneous transmitral pressure difference   pC+I = instantaneous transmitral pressure difference derived from Doppler measurements (including both the convective and inertial components of the unsteady Bernoulli equation)   CMM = color Doppler M-mode   LA = left atrium   LV = left ventricle   sLV or sLA = velocity sample depth within the left ventricle or left atrium   vLV[t] or vLA[t] = velocity profile at the location of a sample volume within the left ventricle or within the left atrium

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