Chronotropic incompetence does not contribute to submaximal exercise limitation in patients with chronic heart failure

The traditional view of the origin of breathlessness and fatigue in patients with chronic heart failure (CHF) includes the concept that a contributing factor might be a limitation to increases in heart rate termed 'chronotropic incompetence' during exercise. In order to examine the relationship of heart rate on workload, we calculated the ratio of workload to heart rate for peak exercise and for steady state tests at 15%, 25% and 50% of peak in controls and CHF patients. The workload/heart rate ratio during the peak tests was lower in patients than control subjects. For each steady state test, patients had a lower absolute workload, and lower oxygen consumption than controls, but the same heart rate at steady state, leading to a lower workload/heart rate ratio in patients than controls. In addition, although we found a relationship between heart rate and workload for control subjects (r = 0.85; p<0.0001), there was no such relationship in patients with chronic heart failure (r = 0.003; p = 0.98) during steady state exercise. Patients with CHF have a lower peak heart rate but a greater heart rate for a given workload during submaximal testing suggesting that heart rate limitation is unlikely to be the cause but rather the consequence of exercise intolerance in CHF patients. (C) 2008 Published by Elsevier Ireland Ltd.