HR
Heart rate (HR) is the speed of the heartbeat, measured as the number of contractions (beats) of the heart per minute (bpm). It adapts constantly to the body's needs — rising with physical activity, emotions, fever or blood loss and falling at rest and during sleep. Resting heart rate is one of the simplest and most informative markers of cardiovascular health and fitness.
How heart rate is regulated
Each heartbeat starts in the sinus node, a small group of pacemaker cells in the right atrium that fire spontaneously at about 100 times per minute. The autonomic nervous system adjusts this intrinsic rate: the vagus nerve (parasympathetic) slows it down and dominates at rest, which is why normal resting heart rate is lower than 100; the sympathetic nerves and the hormones adrenaline and noradrenaline speed it up during exercise, stress or illness. Thyroid hormones, body temperature, blood volume, oxygen level and medicines also influence heart rate.
Heart rate and the volume ejected with each beat (stroke volume) together determine cardiac output — the amount of blood pumped per minute. When demand increases, the heart first raises its rate; in trained people a larger stroke volume allows the same output at a lower rate.
Normal values
| Group | Typical resting heart rate |
|---|---|
| Newborns (0–1 month) | 100–180 bpm |
| Infants (1–12 months) | 100–160 bpm |
| Children 1–10 years | 70–130 bpm (falls with age) |
| Adolescents and adults | 60–100 bpm |
| Well-trained endurance athletes | 40–60 bpm |
| During sleep (adults) | often 45–60 bpm |
Fast heart rate — tachycardia
A resting heart rate above 100 bpm is called tachycardia. Sinus tachycardia is a normal rhythm that is simply fast; it is usually a response to:
- physical exertion, anxiety, pain, caffeine, nicotine, alcohol withdrawal;
- fever, infection, dehydration, blood loss, anaemia;
- overactive thyroid, low blood sugar, pregnancy;
- heart failure, lung disease, pulmonary embolism;
- medicines and drugs: asthma inhalers, decongestants, stimulants.
Tachycardia can also be caused by arrhythmias — atrial fibrillation or flutter, supraventricular or ventricular tachycardia. These often start and stop suddenly, may feel like strong or irregular palpitations and require an ECG for diagnosis.
Slow heart rate — bradycardia
A heart rate below 60 bpm is called bradycardia. In fit people and during sleep it is normal and reflects strong vagal tone. It becomes a problem when the heart cannot supply enough blood — for example in sick sinus syndrome, atrioventricular block, hypothyroidism, hypothermia, increased intracranial pressure or under the influence of medicines (beta-blockers, verapamil, diltiazem, digoxin, antiarrhythmics). Warning symptoms are dizziness, fainting, weakness, shortness of breath, confusion and exercise intolerance.
Resting heart rate and risk
Large epidemiological studies show that a higher resting heart rate predicts cardiovascular and all-cause mortality independently of other risk factors. In a meta-analysis of 46 studies with more than 1.2 million participants, every 10 bpm increase in resting heart rate was associated with a 9 % higher risk of death from any cause and an 8 % higher risk of cardiovascular death; people with a resting rate above 80 bpm had about a 45 % higher all-cause mortality than those with the lowest rates. A high resting heart rate reflects sympathetic predominance, low fitness and higher myocardial oxygen demand.
Heart rate during exercise
During exercise heart rate rises roughly in proportion to effort. Maximum heart rate declines with age and can be estimated by the Tanaka formula:
Moderate-intensity aerobic exercise corresponds to roughly 50–70 % of HRmax, vigorous exercise to about 70–85 %. After stopping exercise, heart rate should fall quickly; a slow recovery (less than about 12 bpm in the first minute) is associated with higher risk and reduced fitness.
When to see a doctor
a fast or slow heart rate is accompanied by chest pain, fainting or near-fainting, severe shortness of breath, confusion, or a sudden very fast irregular rhythm; or if the resting rate is below 40 bpm with symptoms.
your resting heart rate is repeatedly above 100 bpm or below 50 bpm without obvious reason, if you notice frequent palpitations or an irregular pulse, or if your heart rate does not rise normally with exertion. An ECG, Holter monitoring and blood tests (blood count, thyroid hormones, electrolytes) are usually the first steps.
References
- Fox K, Borer JS, Camm AJ, et al. Resting heart rate in cardiovascular disease. J Am Coll Cardiol. 2007;50(9):823–830. doi:10.1016/j.jacc.2007.04.079
- Zhang D, Shen X, Qi X. Resting heart rate and all-cause and cardiovascular mortality in the general population: a meta-analysis. CMAJ. 2016;188(3):E53–E63. doi:10.1503/cmaj.150535
- Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am Coll Cardiol. 2001;37(1):153–156. doi:10.1016/S0735-1097(00)01054-8
- Cole CR, Blackstone EH, Pashkow FJ, Snader CE, Lauer MS. Heart-rate recovery immediately after exercise as a predictor of mortality. N Engl J Med. 1999;341(18):1351–1357. doi:10.1056/NEJM199910283411804
- Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382–e482. doi:10.1161/CIR.0000000000000628
This article is for general information and does not replace a consultation with a doctor.
Published on 30 May 2019