978-120 Exercise Performance in Moderate Mitral Stenosis is Limited by Cardiac Output Reserve Rather than Maximal Pulmonary Capillary Wedge Pressure

Abstract

To assess the hemodynamic limitations of exercise in patients with mitral stenosis (MS), 29 patients with MS (mean age 49, mean valve area 1.4 cm 2 ) and 29 age matched controls underwent symptom limited upright bicycle exercise with simultaneous expired gas analysis, right heart catheterization and radionuclide angiography. Supine rest hemodynamics and left ventricular volumes were abnormal in MS patients compared to control. Despite maximal (MAX) exercise effort, MS patients achieved a lower MAX heart rate (HR) and oxygen consumption (VO 2 /kg) compared to control. With exercise. other intergroup differences were accentuated, especially for MAX cardiac index (CI), pulmonary capillary wedge pressure (PCWP), and end-diastolic volume index (EDVI) Rest and Exercise Hemodynamics VO 2 kg HR PCWP CI EDVI REST MS 2.6 75.8 19.1 2.4 51.5 Control 3.4 68.4 8.2 3.4 76.6 MAX MS 10.4 131.0 29.1 4.0 43.1 Control 23.5 162.3 8.4 7.8 65.2 Mean values shown (p ≤ 0.05 MS vs Control for all values) For the MS group, MAX VO 2 /kg was predicted by MAX CI (r = 0.6) but not by MAX PCWP. Exercise was limited by fatigue rather than shortness of breath in 18/29 patients in the MS group, suggesting a low output state as a reason for exercise termination. No difference was seen in MAX PCWP between patients stopping due to fatigue and those stopping due to shortness of breath (27.3 vs 32.0 mmHg, p = 0.4). Exercise tolerance in patients with moderate mitral stenosis is not limited by MAX PCWP but by failure to augment cardiac output due to abnormal left ventricular diastolic filling and to chronotropic incompetence.