Patients with CHF have a reduced heart rate rise on exercise (chronotropic incompetence). Different methods of defining chronotropic incompetence lead to different estimates of its prevalence. Previous estimates based on %Max‐PPHR had suggested that < 30% of patients with CHF had chronotropic incompetence.14
Our data suggest that 32% of patients not yet taking β blockers have chronotropic incompetence when defined by < 80% Max‐PPHR and 64% have it as defined by < 80% HRR. In β blocked patients the figures are higher: 49% with %Max‐PPHR and 75% with %HRR.
Chronotropic incompetence was related to the severity of heart failure as measured by symptom assessment (New York Heart Association class) and pVo2
. Patients with chronotropic incompetence had a lower pVo2
and a steeper Ve
slope. We found a close relation between pVo2
and %HRR, %Max‐PPHR, and HRR in patients whether or not they were taking β blockers. These results support previous data that chronotropic incompetence is linked to the severity of heart failure. It was thought that chronotropic incompetence may be an important cause of the reduction in exercise capacity in patients with CHF, but previous work and the present study do not support this view.20
Patients with chronotropic incompetence did have reduced exercise capacity but the slope relating heart rate to pVo2
was the same for those with and without chronotropic incompetence. This suggests that at matched work loads, the heart rates were similar and that reduced heart rates may merely reflect work being performed or, in incremental tests, the duration of exercise. Patients taking β blockers had significantly lower PHRs and more chronotropic incompetence than those not taking β blockers, with no overall difference in pVo2
despite a longer exercise time. Longitudinal studies examining the effects of acute and long term β blockade on patients with heart failure have not shown a reduction of pVo2
despite reductions in PHR with β blockers.20,21
Poor chronotropic response to exercise predicts a poor outcome in patients having stress myocardial perfusion scans, independent of severity of coronary disease and LV function.22,23,24,25,26,27
In patients with heart failure chronotropic incompetence is associated with poor heart rate variability and disturbed cardiac autonomic status.28,29
%HRR, perhaps because it includes the RHR, may be useful in populations treated with heart rate limiting agents. It is possibly a more reliable marker of prognosis than percentage maximum predicted heart rate in patients undergoing myocardial perfusion scanning and may therefore also be more useful in assessing the modern heart failure population, many of whom will be taking a β blocker, than measures based on percentage of predicted heart rate.30
The present study is the first to use this calculation in a large heart failure population taking contemporary drugs.
Assessing chronotropic response in patients with CHF may not only be important as a simple way to further stratify patients at higher risk of cardiac death. Data also suggest that chronotropic incompetence can be improved with physical training. The identification of patients with chronotropic incompetence may allow further targeting of medical and device therapy and exercise training to those who will most benefit from it.31
Previous data have suggested that the presence of chronotropic incompetence may be a more powerful predictor of mortality than pVo2
It has also been suggested in a review of 127 patients with CHF that for patients who tolerate β blockers, pVo2
is not useful for predicting mortality.32
In our study, pVo2
was a stronger predictor of mortality than %HRR and %Max‐PPHR, and patients who died during follow up had lower pVo2
and steeper Ve
slopes than those who survived, whether they were taking β blocker at baseline or not.
The heart rate slowing effects of β blockade are important in improving prognosis: patients with greater heart rate reductions gain additional prognostic benefits.33,34
No data on the influence of heart rate reductions during exercise and outlook in patients with CHF have been published. However, higher sympathetic hormone concentrations during exercise are associated with a worse outcome.35
Recent small non‐randomised studies have suggested that target doses and heart rate lowering may be less important and that any dose of β blocker may be sufficient to improve outlook.36,37
In our study, among patients not taking β blockers at the time of the test, chronotropic incompetence or a poor heart rate response to exercise was associated with increased mortality over the subsequent three years. In contrast, patients taking a β blocker with a poor heart rate response to exercise did not have a higher mortality. Patients taking a β blocker with a lower heart rate response to exercise, implying more aggressive β blockade, did not have a worse outcome, even though the pVo2
was lower in patients with %HRR < 80%. Pure heart rate limiting agents without some of the potential side effects or contraindications of β blockers are under investigation and may be useful for patients unable to tolerate β blockade.38
Our data support the concept that chronotropy is not a major factor in determining exercise capacity in patients with CHF, and chronotropic limitation may be an important goal for patients taking β blockers. It is therefore not surprising that pVo2
remains an important predictor of mortality in patients treated with β blockers.
Chronotropic incompetence is common among patients with CHF and its prevalence is greater among patients taking β blockers. Patients with more severe symptoms of CHF and greater reductions in exercise tolerance have a greater reduction in heart rate response to exercise and a higher mortality. pVo2 was the most powerful and consistent predictor of mortality in all subgroups of patients including patients taking β blockers. Patients with chronotropic incompetence who were not taking β blockers had a higher mortality than those without. Chronotropic incompetence due to aggressive β blocker treatment does not predict mortality.