Heart rate is the number of times the heart beats per minute (bpm). In healthy adults at rest, a normal heart rate falls between 60 and 100 bpm. Heart rate varies with age, fitness level, body position, emotion, temperature, and physiological state; it is typically higher in children and lower in very fit athletes, who may have resting rates well below 60 bpm.
The heart rate is set primarily by the sinoatrial (SA) node, the heart’s natural pacemaker, which fires spontaneously at a basal rate and is continuously modulated by the autonomic nervous system. The sympathetic nervous system increases heart rate (such as during exercise, stress, or pain) via release of adrenaline; the parasympathetic nervous system slows it (such as during rest or sleep) via the vagus nerve. Heart rate can be measured by feeling the pulse at the wrist or neck, and is precisely measured by an ECG, heart rate monitor, or pulse oximeter.
Heart rate is important in the assessment and management of several cardiac conditions. A persistently elevated resting heart rate (tachycardia, above 100 bpm) can indicate arrhythmia, fever, heart failure, or anaemia. A very slow heart rate (bradycardia, below 60 bpm when symptomatic) may indicate conduction system disease or medication effects. In atrial fibrillation, the heart rate is characteristically irregular as well as often rapid. In patients with an ICD or pacemaker, the device continuously monitors heart rate and responds to dangerous rhythms automatically.
After cardiac arrest, heart rate monitoring is a constant feature of intensive care management. During cardiac rehabilitation, exercise heart rate targets are set based on the individual’s condition and medications. Beta-blockers, widely used after cardiac arrest, lower resting heart rate and blunt the heart rate response to exercise, which must be accounted for when assessing exercise intensity.
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