Correlates and prognostic implication of exercise capacity in chronic congestive heart failure

Abstract

Previous studies have shown poor correlations between exercise tolerance and measurements of left ventricular (LV) function during rest in patients with congestive heart failure (CHF). To further evaluate the determinants of exercise tolerance and their relation to prognosis, we performed rest and exercise hemodynamic measurements and blood pool scintigraphy in 27 patients with CHF. All patients were treated with digitalis and diuretic drugs, but not vasodilator drugs. Exercise capacity was assessed by maximal oxygen consumption (V̇O 2max) during upright bicycle ergometry. Both right ventricular (RV) and LV ejection fractions were measured by radionuclide techniques, and arterial, right atrial and pulmonary artery pressures, cardiac output, and derived hemodynamic indexes were determined. As a group, patients with severely impaired exercise tolerance (group 1, V̇O 2max less than 10 ml/min/kg) had significantly higher rest pulmonary capillary wedge and right atrial pressures (30 ± 4 vs 23 ± 6 and 12 ± 4 ys 7 ± 2 mm Hg, respectively) than those with a V̇O 2max of 10 to 18 ml/min/kg (group 2). They also had lower LV and RV ejection fractions (16 ± 4% vs 21 ± 4% and 19 ± 12% vs 27 ± 7%, respectively). However, overlap among individual patients was considerable, and only pulmonary capillary wedge pressure at rest correlated significantly (r = 0.69, p < 0.001) with V̇O 2max. During exercise, patients in group 1 had lower heart rates, stroke indexes and cardiac indexes (117±10vs 133 ± 14 beats/min, 25 ± 5 vs 31 ± 7 ml/m 2 and 2.8 ± 0.5 vs 3.9 ± 0.6 liters/min/m 2, respectively), and higher right atrial pressures (18 ± 4 vs 11 ± 5 mm Hg). Both exercise heart rate and cardiac index correlated significantly with V̇O 2max. Patients in group 1 had a significantly higher mortality rate during the subsequent year compared with those in group 2 (77% vs 21%, p < 0.001). Thus, exercise tolerance in CHF appears to be most closely related to the patients' ability to increase their heart rate and cardiac index. Measurements of cardiac function at rest, although worse in patients with severely impaired exercise tolerance as a group, correlate poorly with exercise V̇O 2max in individual subjects. Nonetheless, exercise capacity provided important prognostic information, in that patients with poor tolerance had a significantly higher mortality rate during the first year of follow-up.