Bradycardia
0Bradycardia, by Wikipedia https://en.wikipedia.org/wiki?curid=5872 / CC BY SA 3.0
#Cardiac_arrhythmia
#Symptoms_and_signs:_Cardiac
Bradycardia in adults means their resting heart rate is under 60 beats per minute （BPM）, although some studies use a heart rate of less than 50 BPM. Bradycardia typically does not cause symptoms until the rate drops below 40 bpm.
When symptomatic, it may cause fatigue, weakness, dizziness, sweating, and at very low rates, fainting.
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 to refer to a heart rate that, although not actually below 60 BPM, is still considered too slow for the individual's current medical condition.
The word "bradycardia" is from the Greek βραδύς bradys "slow", and καρδία kardia "heart".
Illustration comparing the EKGs of a healthy person （top） and a person with bradycardia （bottom）: The points on the heart where the EKG signals are measured are also shown.
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 vo...
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