The exercise response in idiopathic dilated cardiomyopathy

In order to more clearly define the exercise response of idiopathic dilated cardiomyopathy (IDC), 20 patients in this study with strictly defined IDC were evaluated with radionuclide ventriculography and invasive hemodynamic monitoring. Severe cardiovascular impairment was present at rest, and peak supine exercise produced progressive left ventricular (LV) dilatation in both diastole and systole (mean±SEM from 172±14 to 212±22 ml/m² at end-diastole and from 137± 14 to 170±22 ml/m² at end-systole; both p<0.03). There were marked increases in LV and right ventricular filling pressure (from 17±2 to 36±3 mmHg and from 7±2 to 15±2 mmHg, respectively; both p<0.0001) and increased pulmonary artery pressure. Mean LV ejection fraction did not change significantly with exercise (22±2 to 23±3%; p>0.8), but individual patients demonstrated substantial variability. Cardiac output rose less than in normals and increases were brought about primarily by subnormal heart rate increases. High resting and exercise systemic and pulmonary vascular resistance were indicative of limited vasodilator reserve. Despite marked hemodynamic abnormalities, 10 of the 20 subjects had well preserved exercise capacity (≥ 12 min exercise duration). These patients as a group had significantly lower resting heart rate and higher exercise cardiac output and lower exercise systemic vascular resistance. However, they did not differ from the other patients with respect to resting LV function. Thus, the exercise response in IDC has specific characteristics that distinguish it from normal and from the exercise response of other causes of LV dysfunction. An interesting subset of patients with IDC has well preserved exercise capacity associated with greater chronotropic and vasodilator reserve. This finding suggests less sympathetic activation in these subjects.