Exercise testing and training in patients with chronic heart failure

Chronic heart failure (CHF) is a syndrome of impaired left ventricular (LV) function and cardiac output reserve that is associated with secondary compensatory adaptations including: LV hypertrophy and dilation, neuroendocrine activation, and vasoconstriction and redistribution of peripheral blood flow. The primary limitation in CHF is exercise intolerance characterized by fatigue and/or dyspnea during mild to moderate exertion. These symptoms are primarily attributed to impaired nutrient blood flow, cellular atrophy, and loss of oxidative function in skeletal muscle. Functional capacity in CHF is usually classified into four categories determined by symptom-limited exercise testing: normal > or = 7 METs; mild 5-7 METs; moderate 3-5 METs, severe < 3 METs. Exercise capacity in CHF is frequently unrelated to resting or exercise measures of LV function, e.g., LV ejection fraction (LVEF) and LV end diastolic pressure (LVEDP). Peak exercise heart rate and blood pressure are progressively attenuated in CHF due to baroreflex dysfunction and beta-receptor down regulation. Exercise training studies in selected patients with CHF (mild to moderate) have reported significant increases in peak VO2max, attributed to increases in peak leg blood flow O2 transport. Heart rate and lactate production during submaximal exercise are reduced compared with pretraining values. Potential training complications in patients with CHF include dysrhythmia, hypotension, and deterioration of cardiac status. The major benefit of moderate exercise training is improvement in tolerance to daily activities. However, the long term effect of exercise training on prognosis is currently not established.