Abstract 19397: Factors Affecting Exercise Capacity in Diabetic Heart Failure Patients

Abstract

Background: Exercise intolerance is a key feature of chronic heart failure (CHF). CHF patients with concomitant diabetes (CHF-DM) have heightened exercise intolerance, poorer prognosis and worse symptoms. Causative mechanisms may be impaired ventilatory, cardiac or skeletal muscle function. We prospectively assessed factors affecting exercise capacity in CHF and CHF-DM. Methods: Stable CHF (n=33) and CHF-DM (n=33) patients with left ventricular systolic dysfunction (ejection fraction (EF) <50%; NYHA class I-II; optimal device and medical therapy), were matched for age (mean±SD: 76±7 yr), weight (85±13 kg), height (1.72±0.06 m), systolic function (EF: 38±11%) and diastolic function (EA ratio 0.9±0.2). They underwent peak cardiopulmonary exercise testing with breath-by-breath pulmonary gas exchange analysis. Exertional shortness of breath (S) symptoms were recorded using the standardized Borg 0-10 scale. Continuous variables were reported as means (SD) and analysed using ANCOVA, categorical variables were analysed using the chi-squared test. A p-value of < 0.05 was taken as significant. Results: CHF-DM had reduced exercise capacity (pVO2 13.9±4.3 v 17.5±5.9 ml/kg/min; p=0.01) and lower exercise time (354±209 v 511±250s; p=0.01). Cardiac and ventilatory responses did not differ: Heart rate rise (44±5 v 46±4 bpm; p=0.21), Ve/VCO2 (37.2±9.4 v 39.5±10.5; p=0.35), peak respiratory frequency (31.7± 6.7 v 31.1± 7.6 breaths/min; p=0.76). Symptoms did not differ at baseline, peak or during exercise (Peak Borg S: 4±2 v 4±2; p= 0.73) The lactate threshold (LT) (9.86±0.27 v 11.26 ±0.32 L/min; p=0.48), time to LT (358 ± 92.58 v 393 ± 203.94 s; p=0.22) and the respiratory compensation point (RCP) (12.77±0.37 v 14.37± 0.45 L/min; p=0.64) did not differ. Conclusion: Exercise capacity is reduced in CHF-DM subjects matched for age, BMI and cardiac function. There are no differences in symptoms of breathlessness, Ve/VCO2 slope or respiratory rate. However, LT and time to LT is unchanged, despite lower exercise time overall. Thus, there is an inability to tolerate exercise beyond the LT. This is likely due to altered skeletal mitochondrial function in the context of concomitant diabetes.