Original Articles
Calculation of mitral regurgitant orifice area with use of a simplified proximal convergence method: Initial clinical application*

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Abstract

To validate a previously proposed simplified proximal flow convergence method for calculating mitral regurgitant orifice area (ROA), a prospective study was conducted in ambulatory patients and in patients undergoing open heart surgery. Assuming a pressure difference between the left ventricle and left atrium of approximately 100 mm Hg (jet velocity [vp] 500 cm/s) and setting the color aliasing velocity (va) to 40 cm/s, we simplified the conventional proximal convergence method formula (ROA = 2πr2va/vp) to r2/2, where r is the radius of the proximal convergence isovelocity hemisphere. For 57 ambulatory patients with a wide range of mitral regurgitant severity (1 to 4+), ROA was calculated by the conventional (x) and simplified (y) methods, demonstrating excellent accuracy (r = 0.92; P <.001; ΔROA [y − x] = 0.004 ± 0.08 cm2). For 24 intraoperative patients, ROA calculated by the simplified formula (y) correlated well with the pulsed Doppler-thermodilution method (x) (r = 0.84; P <.01; ΔROA [y − x] = −0.002 ± 0.08cm2). This simplified proximal convergence formula yields an accurate assessment of ROA for a wide range of regurgitant severity, while the time required for this measurement is shortened by half (1.5 ± 0.5 minutes versus 3.2 ± 0.7 minutes). This may increase the frequency of calculating ROA in the clinical laboratory. (J Am Soc Echocardiogr 2001;14:180-5.)

Introduction

In the past decade, management of mitral regurgitation has evolved considerably, with early surgical intervention recommended if mitral valve repair appears technically feasible.1, 2 A key to optimal timing of surgery is an accurate assessment of valve morphology and quantification of regurgitant magnitude. Two-dimensional and Doppler echocardiography have achieved a preeminent role in the preoperative evaluation of mitral valve disease and the intraoperative guidance of mitral valve repair.3, 4, 5 Although semiquantitative methods (such as those requiring calculation of the area of the regurgitant jet by color Doppler3, 4, 5, 6, 7 or the diameter of the vena contracta8) are useful in separating significant from nonsignificant valve disease, accurate timing of surgery demands more quantitative indexes, such as regurgitant flow, volume, and fraction and especially the regurgitant orifice area (ROA)—perhaps the purest index of valve incompetence.

Regurgitant orifice area may be calculated in a variety of ways, including a combination of 2-dimensional and pulsed Doppler echocardiography measurements9 and the proximal flow convergence method.10, 11 Although the proximal convergence method has been validated in numerous in vitro and clinic studies,10, 11, 12, 13 it has not been widely applied in routine clinical practice, partly because of the need for multiple measurements and somewhat complex computations. We have proposed an algorithm to calculate ROA with a simplified approach,14 but this has not been rigorously validated in the clinical setting. We therefore carried out this prospective study to determine the speed, accuracy, and limitations with which ROA can be calculated by the simplified proximal flow convergence method.

Section snippets

Patients and data acquisition

The study population included 57 ambulatory patients (34 men, 23 women; mean age 66 ± 13 years) and 24 patients who underwent open heart surgery (16 men, 8 women; mean age 61 ± 15 years). The causes of mitral regurgitation included primary mitral valve diseases (n = 22), coronary artery disease (n = 37), and cardiomyopathy (n = 12), among others (n = 10). Transthoracic echocardiography was performed in ambulatory patients, and intraoperative transesophageal echocardiography was performed in the

Results

In the ambulatory patients, ROA varied from 0.05 to 0.72 cm2 and mean peak mitral regurgitant velocity was 487 ± 57 cm/s; intraoperative ROA ranged from 0.02 to 0.50 cm2, with a mean peak mitral regurgitant velocity of 470 ± 44 cm/s, comparing favorably with the 500 cm/s assumed by the simplified formula.

In ambulatory patients, ROA calculated by the simplified proximal flow method correlated well with that calculated by the conventional method (r = 0.92, P <.001) (Figure 2, A).

. A, Correlation of

Discussion

Color Doppler echocardiography was initially used to assess mitral regurgitation in a semiquantitative manner by measuring regurgitant jet area within the left atrium. Such a qualitative approach remains valuable, allowing a rapid differentiation between mild, moderate, and severe regurgitation. However, the quantitative limitations of the jet area method are well known, including load dependence,17 the impact of instrument factors,18 and jet eccentricity.19

In recent years, early surgical

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    *

    Reprint requests: James D. Thomas, MD, FACC, Department of Cardiology, Desk F15, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195-5064 (E-mail: [email protected]).

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