Does balloon mitral valvuloplasty improve cardiac function? A mechanistic investigation into impact on exercise capacity

Abstract

Procedural technical success of balloon mitral valvuloplasty (BMV) is indicated by an increase in valve area and a reduction in transvalvar gradient, but there are conflicting results regarding whether these indicators correlate with subsequent improvements in exercise capacity. We conducted a study to explore the effects of valvuloplasty on cardiac function to gain insight into the mechanisms responsible for the impact on exercise ability. Sixteen patients with mitral stenosis participated in the study and the five who did not proceed to valvuloplasty served as the control group. All patients performed maximal cardiopulmonary exercise tests before and 6 weeks after valvuloplasty (without valvuloplasty in controls). Central haemodynamics including cardiac output were measured non-invasively at rest and peak exercise. At baseline, the cardiopulmonary exercise test results were similar in the two groups. Following valvuloplasty, cardiac output did not alter at rest, but increased significantly at peak exercise (8.7±1.7 to 10.5±2.1 l min −1, P<0.01), as did peak cardiac power output (1.88±0.55 to 2.28±0.74, P<0.05) and cardiac reserve (1.07±0.33 to 1.45±0.55 watts, P<0.05). Aerobic exercise capacity improved (13.9±4.2 to 16.4±4.3 ml kg −1 min −1, P<0.01) as did exercise duration (354±270 to 500±266 s, P<0.01). There were no significant changes in the controls. There was a significant correlation between the changes in peak VO 2 and changes in cardiac reserve ( r=0.62, P<0.01) but not with changes in resting haemodynamics. These changes did not correlate with changes in peri-procedural mitral valve haemodynamics, despite increases in mitral valve area from 1.05±0.16 to 1.74±0.4 cm 2 ( P<0.0001), accompanied by falls in the transvalvar gradient and pulmonary artery pressure (12.4±4.7 to 4.5±3 mmHg, and 26.8±8.4 to 17.4±5.2 mmHg, respectively, all P<0.0001). In conclusion, we found that successful mitral valvuloplasty in our patient cohort led to improved cardiac and physical functional capacity but not resting haemodynamics. Neither indicators of technical success nor resting haemodynamics were very reliable in predicting functional improvement.