Decreases in left atrial compliance during early-stage exercise are related to exercise intolerance in asymptomatic significant mitral stenosis.

BACKGROUND

Doppler-driven net atrioventricular compliance (C ), which represents left atrial (LA) compliance, is an important determinant of pulmonary hypertension in mitral stenosis (MS).

HYPOTHESIS

We hypothesized that decreases in C during early-stage exercise underlie exercise intolerance in patients with MS.

METHODS

Thirty-three asymptomatic patients with significant MS (valve area 1.24 ± 0.16 cm ) underwent resting and bicycle exercise echocardiography. LA compliance and conventional parameters were assessed at each workload. The patients were classified into two groups based on whether they developed dyspnea during exercise: an exercise-intolerance group (n = 22) and an exercise-tolerance group (n = 11). Moreover, "50 W" was defined as an early exercise stage.

RESULTS

Although the groups had similar resting characteristics, there were striking differences in their echocardiographic parameters from the early stages of exercise. The relative C decrease at 50 W (expressed as a percentage of the resting C ) was significantly greater in the exercise-intolerance group (70.3 ± 15.4% vs 49.7 ± 9.7%, P < .001). The overall decrease in relative C was significantly greater in the exercise-intolerance group (P = .0005). Furthermore, differences in the trends in this parameter were observed between the two groups (P < .0001 for interaction). Multivariate analysis revealed that the relative C decrease at 50 W was an independent predictor of exercise intolerance (adjusted OR 1.105, 95% CI 1.030-1.184) after adjustment for other conventional parameters.

CONCLUSIONS

Decreases in C during early-stage exercise are an important mechanism underlying exercise intolerance in MS.