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What are Bradycardia Causes?

By H. Colledge
Updated Mar 03, 2024
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The term bradycardia, sometimes known as sinus bradycardia, means a person has a heart rate of less than 60 beats each minute while resting. There are a number of bradycardia causes, and it is possible for the condition to be normal when found in a healthy young person or an athlete. Abnormal bradycardia causes generally lead to symptoms such as chest pain and breathlessness, feeling dizzy, fainting and having difficulty exercising. A common cause of bradycardia is a condition known as sick sinus syndrome, where there is a problem with the conduction of the electrical impulses which spread through heart muscle and cause it to contract. Other causes of bradycardia include drugs, hypothermia, an underactive thyroid gland and sleep apnea, where a person repeatedly stops breathing while asleep.

Diagnosis of bradycardia causes involves examining a person for physical signs and asking about symptoms such as being short of breath while exercising. Typically, an athlete for whom bradycardia is normal will be able to undertake heavy exercise without too much distress, while a person with abnormal bradycardia will suffer shortness of breath with only moderate exertion. Investigations such as an ECG, or electrocardiogram, may reveal problems with the electrical conduction of the heart, or conditions such as a heart attack or angina, which are also possible causes of sinus bradycardia.

Bradycardia causes include some medications given for heart problems, including digoxin, which is used to treat irregular heart rates or heart failure, and beta blockers, which may be prescribed for high blood pressure or angina. Lithium, used in the treatment of mental illness, is another possible bradycardia cause. If symptoms are severe, in order to treat the bradycardia it might be necessary to stop using a particular drug.

One of the most common bradycardia causes, a condition known as sick sinus syndrome, may occur following a decrease in the blood supplied to heart tissue. It can also arise when problems affect the heart's natural pacemaker tissue or where a heart abnormality is present from birth. The condition most often occurs in elderly people who have existing heart disease, and bradycardia is generally seen to alternate with its opposite, tachycardia, where the heart rate becomes abnormally fast. A person with the disorder may experience weakness, dizziness and fainting, and treatment usually involves having an artificial pacemaker surgically implanted to maintain a regular heartbeat.

In many cases, bradycardia can be treated by attending to the underlying cause, but when bradycardia is severe enough to cause heart failure, emergency treatment is required. This may involve administering oxygen. Sometimes a drug known as atropine is given by injection in order to increase the heart rate. A temporary pacemaker may be used in extreme cases.

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Discussion Comments
By ddljohn — On Jul 28, 2014

I didn't know that a heart attack can cause a slow heart rate. For some reason, I thought the opposite would be true. But it makes sense actually. If the coronary arteries are blocked, less blood will reach the heart, which will slow it down.

I guess those with heart disease who have bradycardia should take it very seriously and have it checked out immediately. Even if a medication is causing the low heart rate, I think it should be attended to quickly. I would not want to ignore this symptom.

By candyquilt — On Jul 27, 2014

@donasmrs-- I'm not an expert on this topic but I suffered from an underactive thyroid for a few years and have experienced this. You see, thyroid hormones produced by the thyroid gland interact with other glands in our body. Together, these hormones help regulate various functions such as metabolism and heart rate. When the thyroid gland does not produce enough thyroid hormones, some of these functions, including heart rate, can slow down. That's how an underactive thyroid leads to bradycardia.

It's difficult to know what the exhaustion is caused by. Since hypothyrodism causes the metabolism to slow down as well, that can also cause someone to be tired. A slow heart rate will make someone tired too. So this symptom may actually be a result of both conditions. Treating the underlying cause, that is, the underactive thyroid, will treat the bradycardia as well.

By donasmrs — On Jul 27, 2014

How does an underactive thyroid gland lea to bradycardia? Is this the reason why people who have this condition are so tired and exhausted all the time?

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