Chronotropic incompetence (CI) is the inability of heart rate to increase as expected in response to exercise. In healthy people, cardiac output during exercise increases via a rise in both heart rate and stroke volume. When the heart rate does not rise sufficiently, this can lead to exercise intolerance. CI can be detected using a cardiopulmonary exercise test.[1] People with CI have a higher risk of cardiovascular disease and early death.[1]
There are different ways to define CI. One common threshold is not being able to reach 80% of age-predicted maximal heart rate (APMHR). APMHR is said to be 220 – age. Another one is not being able to reach 80% of the expected heart rate reserve, that is, the difference between the individual's resting heart rate and the APMHR.[1]
Chronotropic incompetence occurs in various diseases. Roughly half of people with heart failure experience it, compared to less than 9% of age-matched healthy controls.[2] When it occurs alongside issues with stroke volume, it can leading to a strong decrease in functional ability.[1] It is associated with the activation of the sympathetic nervous system (part of the fight-or-flight response) leading to higher levels of norepinephrine. CI in people with heart failure can further be related to the use of β-blockers, a high resting heart rate or the downregulation of β-adrenergic receptors.[3]