Chronotropic incompetence (CI) is the inability of

heart rate Heart rate is the frequency of the cardiac cycle, heartbeat measured by the number of contractions of the heart per minute (''beats per minute'', or bpm). The heart rate varies according to the body's Human body, physical needs, including the nee ...

to increase as expected in response to

exercise Exercise or workout is physical activity that enhances or maintains fitness and overall health. It is performed for various reasons, including weight loss or maintenance, to aid growth and improve strength, develop muscles and the cardio ...

. The condition can be defined in different ways and occurs in various diseases. Sufferers have a higher risk of

cardiovascular disease Cardiovascular disease (CVD) is any disease involving the heart or blood vessels. CVDs constitute a class of diseases that includes: coronary artery diseases (e.g. angina, heart attack), heart failure, hypertensive heart disease, rheumati ...

and early death.

Definition

In healthy people,

cardiac output In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols Q, \dot Q, or \dot Q_ , edited by Catherine E. Williamson, Phillip Bennett is the volumetric flow rate of the heart's pumping output: tha ...

during exercise increases via a rise in both heart rate and

stroke volume In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the ventricle (heart), ventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from an Echocardiography, echocardiogram and subtra ...

. When the heart rate does not rise sufficiently, this can lead to

exercise intolerance Exercise intolerance is a condition of inability or decreased ability to perform physical exercise at the normally expected level or duration for people of that age, size, sex, and muscle mass. It also includes experiences of unusually severe pos ...

. CI can be detected using a cardiopulmonary exercise test. People with CI have a higher risk of cardiovascular disease and early death. There are different ways to define CI. One common threshold is not being able to reach 80% of age-predicted maximal heart rate (APMHR), which is said to be 220 – age. Another definition is not being able to reach 80% of the expected

heart rate reserve Heart rate is the frequency of the heartbeat measured by the number of contractions of the heart per minute (''beats per minute'', or bpm). The heart rate varies according to the body's physical needs, including the need to absorb oxygen and ex ...

, that is, the difference between the individual's

resting heart rate Heart rate is the frequency of the heartbeat measured by the number of contractions of the heart per minute (''beats per minute'', or bpm). The heart rate varies according to the body's physical needs, including the need to absorb oxygen and ...

and APMHR.

Incidence

Chronotropic incompetence occurs in various diseases. Roughly half of people with

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome caused by an impairment in the heart's ability to Cardiac cycle, fill with and pump blood. Although symptoms vary based on which side of the heart is affected, HF ...

experience it, compared to less than 9% of age-matched healthy controls. When CI occurs alongside issues with stroke volume, it can lead to a strong decrease in functional ability. It is associated with the activation of the

sympathetic nervous system The sympathetic nervous system (SNS or SANS, sympathetic autonomic nervous system, to differentiate it from the somatic nervous system) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous sy ...

(part of the

fight-or-flight response The fight-or-flight or the fight-flight-freeze-or-fawn (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first describ ...

), leading to higher levels of

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic compound, organic chemical in the catecholamine family that functions in the brain and human body, body as a hormone, neurotransmitter and neuromodulator. The ...

. CI in people with heart failure can further be related to the use of

β-blockers Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms ( arrhythmia), and to protect the heart from a second heart attack after a first heart attack (secondary prevention) ...

, a high resting heart rate or the

downregulation In biochemistry, in the biology, biological context of organisms' regulation of gene expression and production of gene products, downregulation is the process by which a cell (biology), cell decreases the production and quantities of its cellular ...

β-adrenergic receptors The adrenergic receptors or adrenoceptors are a class of G protein-coupled receptors that are targets of many catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) produced by the body, but also many medications like bet ...

. CI is also observed in people with

obstructive sleep apnea Obstructive sleep apnea (OSA) is the most common sleep-related breathing disorder and is characterized by recurrent episodes of complete or partial airway obstruction, obstruction of the respiratory tract#Upper respiratory tract, upper airway lea ...

. Similarly to CI in heart failure, it is possibly linked to the

autonomic nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...

shift towards the sympathetic nervous system. People with type-2 diabetes often experience CI too, as do some people with

long COVID Long may refer to: Measurement * Long, characteristic of something of great duration * Long, characteristic of something of great length * Longitude (abbreviation: long.), a geographic coordinate * Longa (music), note value in early music mens ...

. People with

myalgic encephalomyelitis/chronic fatigue syndrome Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a disabling Chronic condition, chronic illness. People with ME/CFS experience profound fatigue that does not go away with rest, as well as sleep issues and problems with memory ...

(ME/CFS) also experience a blunted heart rate response to exercise. CI in ME/CFS is most evident on the second day of a repeated exercise test, after the first exercise test induces

post-exertional malaise Post-exertional malaise (PEM), sometimes referred to as post-exertional symptom exacerbation (PESE) or post-exertional neuroimmune exhaustion (PENE), is a worsening of symptoms that occurs after minimal exertion. It is the hallmark symptom of m ...

References

{{reflist Cardiovascular physiology