Mitral Valve Reserve Capacity in Mitral Stenosis and Clinical Implications

In normal subjects, the increased mitral valve flow with exercise is accomplished by an increase in maximum diastolic mitral valve orifice (mitral valve reserve capacity). It is generally accepted that in rheumatic mitral stenosis, the stenotic mitral valve orifices is fixed in a maximally opened position in diastole with no reserve capacity. However, as shown recently, patients with milder degrees of mitral stenosis may have some residual reserve capacity allowing mitral valve area to increase during exercise. Patients with milder mitral stenosis and more pliable mitral leaflets (as evaluated by echo scoring) can increase their mitral valve area significantly on supine exercise as compared to those with more severe degree of valvular narrowing. On the other hand, the restoration of mitral valve reserve capacity after mitral balloon valvulotomy may be important in increasing the mitral valve flow without further elevation of transmitral pressure gradient, thereby contributing to the symptomatic improvement of the patients. Moreover, this phenomenon may have importance in defining restenosis after mitral balloon valvulotomy. As we have reported previously, the widely used defition of restenosis based on rest hemodynamics may not correlate with the symptomatic status during follow-up. Therefore, in evaluating the long term results of mitral valvulotomy, determination of the hemodynamic response to dobutamine may be more clinically relevant than an absolute cut-off value for mitral valve area.