Determinants of delayed improvement in exercise capacity after percutaneous transvenous mitral commissurotomy

Percutaneous transvenous mitral commissurotomy (PTMC) results in short-term hemodynamic and symptomatic improvements. We have previously shown that the immediate symptomatic relief is related to the improvement in excessive exercise ventilation. The exercise capacity, however, does not improve in the short term but does improve gradually over several months. The pathophysiologic basis for the delayed improvement in exercise capacity has not been fully evaluated.

To elucidate the determinants of improvement in exercise capacity late after PTMC, maximal ergometer exercise with respiratory gas analysis and exercise hemodynamic measurements were performed in 22 patients with symptomatic mitral stenosis before, immediately after, and 7 months after PTMC.

Mitral valve area increased from 0.9 +/- 0.2 cm(2) to 1.7 +/- 0.4 cm(2) after PTMC (P <.01). Significant improvements were observed in symptoms, cardiac output at peak exercise (6.6 +/- 1.5 L/min vs 8.6 +/- 1.9 L/min, P <.01), and mean pulmonary artery pressure at peak exercise (54.1 +/- 15.6 mm Hg vs 42.3 +/- 9.5 mm Hg, P <.01) immediately after PTMC. Excessive exercise ventilation, as assessed by the slope of the regression line between expired minute ventilation and carbon dioxide output (VE-VCo(2)), decreased significantly from 38.2 +/- 8.2 to 33.3 +/- 4.9 (P <.01). There were no significant changes in peak oxygen uptake (from 17.5 +/- 3.2 mL/kg per minute to 17.9 +/- 3.6 mL/kg per minute) immediately after PTMC. At 7 months, improved mitral valve area, symptoms, cardiac output at peak exercise, mean pulmonary artery pressure at peak exercise, and VE-VCo(2) were unchanged compared with values immediate after PTMC. Significant improvement was observed in peak oxygen uptake (19.7 +/- 3.0 mL/kg per minute [P <.01 compared with pre-PTMC or immediate post-PTMC values]). The increase in exercise cardiac output or the decrease in pulmonary artery pressure was not correlated with the late improvement in peak oxygen uptake. The short- or long-term improvements in VE-VCo(2), however, were significantly correlated with the late improvement in peak oxygen uptake.

Our results suggest that ventilatory improvement, not increased exercise cardiac output, contributed at least in part to the late improvement in exercise capacity after PTMC.