Bradydysrhythmias
| Bradycardia | |
|---|---|
| Synonyms | bradyarrhythmia, brachycardia |
 |
|
| Sinus bradycardia seen in lead II with a heart rate of about 50. | |
| Pronunciation | |
| Classification and external resources | |
| Specialty | Cardiology |
| ICD-10 | R00.1 |
| ICD-9-CM | 427.81, 659.7, 785.9, 779.81 |
| Patient UK | Bradycardia |
| MeSH | D001919 |
Bradycardia is a condition wherein an individual has a slow heart rate, typically defined as a heart rate of under 60 beats per minute (BPM) in adults. Bradycardia typically does not cause symptoms until the rate drops below 50 BPM. When symptomatic, it may cause fatigue, weakness, dizziness, sweating, and at very low rates, fainting.
During sleep, a slow heartbeat with rates around 40–50 BPM is common, and is considered normal. Highly trained athletes may also have athletic heart syndrome, a very slow resting heart rate that occurs as a sport adaptation and helps prevent tachycardia during training.
The term relative bradycardia is used in explaining a heart rate that, although not actually below 60 BPM, is still considered too slow for the individual's current medical condition.
Bradycardia in an adult is any heart rate less than 60 beats per minute (BPM), although symptoms usually manifest only for heart rates less than 50.
Atrial bradycardias are divided into three types. The first, respiratory sinus arrhythmia, is usually found in young and healthy adults. Heart rate increases during inhalation and decreases during exhalation. This is thought to be caused by changes in the vagal tone during respiration. If the decrease during exhalation drops the heart rate below 60 bpm on each breath, this type of bradycardia is usually deemed benign and a sign of good autonomic tone.
The second, sinus bradycardia, is a sinus rhythm of less than 60 BPM. It is a common condition found in both healthy individuals and those considered well-conditioned athletes. Studies have found that 50–85% of conditioned athletes have benign sinus bradycardia, as compared to 23% of the general population studied. The heart muscle of athletes has become conditioned to have a higher stroke volume, so requires fewer contractions to circulate the same volume of blood.
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