Bradycardia (Greek βραδυκαρδία, bradykardía, "heart slowness"), in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart. It sometimes results in fainting, shortness of breath, and if severe enough, death.
Trained athletes or young healthy individuals may also have a slow resting heart rate (e.g. professional cyclist Miguel Indurain had a resting heart rate of 28 beats per minute). Resting bradycardia is often considered normal if the individual has no other symptoms such as fatigue, weakness, dizziness, lightheadedness, fainting, chest discomfort, palpitations or shortness of breath associated with it.
The term relative bradycardia is used in explaining a heart rate which although not actually below 60 beats per minute still is considered too slow for the individual's current medical condition.
Bradycardia in an adult is any heart rate less than 60 beats per minute. Before it causes symptoms though the heart rate is typically less than 50.
Atrial bradycardias come in three different types. The first is sinus bradycardia. This is usually found in young and healthy adults. The symptoms represent with the individual's respirations. Each inhalation corresponds with the heart rate decreasing. Expiration causes an increase in the heart's rate of contraction. This is thought to be caused by changes in the vagal tone during respiration.
Sinus bradycardia is a sinus rhythm of less than 60 bpm. It is a common condition found in both healthy individuals and those who are considered well conditioned athletes. Studies have found that 50 - 85 percent of conditioned athletes have benign sinus bradycardia, as compared to 23 percent of the general population studied. The reason for this is that their heart muscle has become conditioned to have a higher stroke volume and therefore requires fewer contractions to circulate the same volume of blood.
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