Mitral Valve Resistance as a Determinant of Resting and Stress Pulmonary Artery Pressure in Patients with Mitral Stenosis: A Dobutamine Stress Study

Abstract

Severity of mitral stenosis (MS) is assessed by means of mitral valve area and mean transmitral gradient. However, these conventional stenosis indexes poorly reflect the major hemodynamic consequence of MS, which is increase in pulmonary artery pressure (PAP). Valve resistance (VR) is a physiologic expression of stenosis because it incorporates both the pressure gradient and flow data. Previously, in patients with aortic stenosis, hemodynamic burden on the left ventricle has been shown to be closely related to aortic VR but not to aortic valve area. Accordingly, we hypothesized that mitral VR may also better reflect the hemodynamic burden of MS and, hence, be an important determinant of PAP in patients with MS. This study sought to evaluate the relation between several echocardiographic parameters of MS severity, in particular mitral VR and the resting and stress PAP in patients with MS. Determinants of exercise capacity were also assessed. Twenty patients with pure MS were studied by Doppler echocardiography. Mitral valve area, mean transmitral gradient, mitral VR, net atrioventricular compliance, and left atrial diameter were derived from resting Doppler echocardiographic examination as possible determinants of resting and stress PAP. PAP was measured by Doppler echocardiography at rest and during dobutamine-induced stress. Patients completed a symptom-limited exercise test to determine exercise capacity. Determinants of resting and stress PAP and exercise capacity were analyzed. Systolic PAP increased significantly from 39.2 +/- 9.4 mm Hg at rest to 59.5 +/- 18.4 mm Hg during dobutamine-induced stress. Mitral VR was the most closely correlated stenosis index with the resting and stress PAP (r = 0.80, P < .001 and r = 0.93, P < .001, respectively) and it was an independent predictor for both with multivariate analysis. Exercise capacity was mostly and equally correlated with stress PAP (r = -0.62, P = .004) and mitral VR (r = -0.62, P = .004). Multivariate analysis revealed stress PAP as the only significant independent predictor of exercise capacity. Mitral VR is the strongest and the independent predictor of both resting and stress PAP in patients with MS and by this aspect it is superior to mitral valve area and mean transmitral gradient in the expression of stenosis severity. These results underline the importance of mitral VR as a severity index in patients with MS.