Mechanisms of Effort Intolerance in Patients with Rheumatic Mitral Stenosis: Combined Echo and Cardio-Pulmonary Stress Protocol

Background: Combined stress echo and cardio-pulmonary tests can assess cardiac function, hemodynamics, and oxygen content difference (A-VO₂ Difference) in four predefined activity levels (rest, unloaded, anaerobic threshold [AT], and peak) non-invasively. We aimed to evaluate mechanisms of effort intolerance in patients with rheumatic mitral stenosis (MS) using combined tests.

Methods: Left ventricular volumes, ejection fraction, stroke volume, S`, mitral gradient, mitral area, e`, ventilatory parameters, VO₂, and A-VO₂ Difference were measured in all effort stages using ramp semi-recumbent cycle prolonged (at least 8 minutes) exercise in 20 consecutive subjects with rheumatic MS (mitral area 1.36±0.4) and compared to 20 control subjects matched for age and gender.

Results: In patients with MS, the changes in VO₂ (between group p<0.0001; group by time interaction p<0.0001), heart rate (p<0.0001; p=0.01), stroke volume (p=0.0006; p=0.03), end diastolic volume (p=0.006; p=0.0006), ejection fraction (p=0.01; p=0.009), S` (p<0.0001; p=0.01), e` (p<0.0001; p<0.0001), and tidal volume (p<0.0001; p=0.007) were all attenuated compared to controls. Comparing patients with MS and poor effort intolerance (<80% of expected) to those with better effort tolerance we found that attenuated increase in end diastolic volume (group by time interaction p=0.05), tidal volume (p=0.0003), heart rate (p=0.0009), and mitral area (p=0.04) were typical for patients with poor effort capacity. In multivariable analysis peak heart rate response (P=0.01), tidal volume response (p=0.0001), and peak A-VO₂ Difference (P=0.03) were the only independent predictors of effort capacity in patients with MS, but systolic pulmonary pressure, mitral gradient or area were not.

Conclusions: Patients with rheumatic MS have impaired systolic and diastolic reserve, chrontropic incompetence and attenuated ventilatory response compared to normal individuals. In patients with rheumatic MS, exercise intolerance is predominantly due to restrictive lung function, chronotropic incompetence and peripheral factors, and not just impaired valvular function.