What is the chronotropic (heart rate) response?

From the Guidelines

Chronotropic response refers to the heart's ability to adjust its rate in response to various stimuli, primarily during physical activity or stress, and is crucial for evaluating cardiovascular health and exercise capacity in clinical settings. This response is primarily regulated by the autonomic nervous system, with sympathetic stimulation increasing heart rate and parasympathetic stimulation decreasing it. A normal chronotropic response allows the heart to meet increased oxygen demands during physical exertion by appropriately increasing cardiac output.

Key Points

• Chronotropic incompetence, a condition where the heart fails to increase its rate adequately during exercise, can lead to exercise intolerance and reduced functional capacity.
• This condition is often assessed during exercise stress tests, where a patient's heart rate response to increasing workload is measured.
• Chronotropic incompetence may be caused by aging, heart disease, or medications like beta-blockers that intentionally blunt heart rate increases.
• Understanding chronotropic response is important for evaluating cardiovascular health and exercise capacity in clinical settings, as an abnormal chronotropic response is associated with a poorer prognosis among women than a normal heart rate response 1.

Definition and Assessment

• The simplest approach to define chronotropic response is to report change in HR with exercise relative to peak HR, with an inability to achieve ≥85% of age-predicted maximum HR considered chronotropic incompetence 1.
• An alternative method to determine chronotropic incompetence entails assessment of the proportion of HR reserve used at peak exercise, defined by the difference between age-predicted maximal HR and resting HR 1.

Clinical Importance

• Markers reflective of autonomic nervous system function, such as chronotropic response, can predict major cardiovascular events, total mortality, and sudden cardiac death 1.
• Failure of the heart rate to rise appropriately during exercise has been termed chronotropic incompetence and has been linked to adverse outcome whether or not beta blockers are being taken 1.
• The fall in heart rate immediately after exercise, also known as heart rate recovery, is thought to reflect parasympathetic tone and has been associated with death or cardiac events in a number of populations 1. In clinical practice, it is essential to assess chronotropic response during exercise stress tests to evaluate cardiovascular health and exercise capacity, and to identify patients with chronotropic incompetence who may be at increased risk of adverse outcomes.

From the FDA Drug Label

When access to beta-receptor sites is blocked by propranolol, the chronotropic, inotropic, and vasodilator responses to beta-adrenergic stimulation are decreased proportionately. Glucagon can exert potent inotropic and chronotropic effects and may be particularly useful for the treatment of hypotension or depressed myocardial function after a propranolol overdose Chronotropic response refers to the effect of a substance on the heart rate. In the context of beta blockers, the chronotropic response is decreased, meaning that the heart rate is reduced. This is because beta blockers, such as propranolol, block the beta-adrenergic receptors in the heart, which are responsible for increasing heart rate in response to stimuli.

• The chronotropic response is one of the three main effects of beta-adrenergic stimulation on the heart, along with inotropic (contractility) and vasodilator (blood vessel dilation) responses.
• Glucagon can be used to increase the chronotropic response, particularly in cases of propranolol overdose, by administering it intravenously to produce a positive chronotropic effect 2 2.

From the Research

Definition of Chronotropic Response

• The chronotropic response refers to the heart's ability to increase its rate in response to physical activity or exercise 3, 4, 5, 6, 7.
• It is an important aspect of cardiovascular function, as it allows the heart to meet the increased demand for blood flow and oxygen during physical activity.

Factors Influencing Chronotropic Response

• The chronotropic response is influenced by various factors, including age, fitness level, and the presence of certain medical conditions such as heart failure or sick sinus syndrome 3, 4, 6, 7.
• Beta-blockade, a type of medication commonly used to treat high blood pressure and heart failure, can also impact the chronotropic response 3.

Measurement of Chronotropic Response

• The chronotropic response can be measured using various methods, including exercise testing and heart rate monitoring 3, 4, 5, 6, 7.
• The chronotropic index (CIx) is a measure of the heart's ability to increase its rate in response to exercise, and is calculated as the percentage of heart rate reserve achieved during exercise 4, 5.

Clinical Significance of Chronotropic Response

• An impaired chronotropic response, also known as chronotropic incompetence, has been associated with adverse cardiovascular outcomes, including increased risk of cardiovascular mortality, stroke, and heart failure 3, 4, 5, 6.
• The chronotropic response can be used as a prognostic indicator for cardiovascular risk, and can help identify individuals who may benefit from closer monitoring or intervention 3, 4, 5.