Bradycardia is the medical term for a heart rate that is lower than expected. Bradycardia is a resting heart rate below 60 beats per minute.
A low heart rate is not necessarily bad or even abnormal. Many healthy people have a resting heart rate of 50 to 60 beats per minute. For example, athletes in particular are known for their low heart rates.
However, bradycardia can become a serious problem if the heart rate is so low that the heart stops pumping enough blood to the body. Therefore, this type of pathological bradycardia is medically important and requires careful evaluation and treatment.
This article explains the symptoms, causes, diagnosis, and treatment of bradycardia.
The sinus node is located in the right atrium and is the heart's natural pacemaker. At rest, the sinus node generally generates electrical impulses at a rate of 60 to 100 times per minute. A heart rate in this range is called normal sinus rhythm .
Sinus bradycardia is a heart rate of 50 to 60 beats per minute. While these values are technically outside the normal range, for some people, these values can be completely normal.
A healthy body regulates the heart rate very well to support bodily functions, and a lower heart rate is often within this range.
Psychological bradycardia is considered a harmless form of sinus bradycardia. In other words, the heart rate meets the body's requirements and is not a medical problem.
In healthy young people and even physically fit older people, the resting heart rate is usually 40 to 50 years. It is also common (and normal) for many people to have their heart rate in this range while they sleep.
When the pulse becomes too slow to pump enough blood, treatment is needed. Symptomatic sinus bradycardia is a sign to seek medical attention.
Symptoms of bradycardia
If your heart rate is abnormally low, some organs in your body may not function normally. Too low a heart rate causes a variety of symptoms, including:
These symptoms are worsened by exercise because the body's needs increase when it is stressed. However, symptoms may be present at rest if bradycardia is severe.
If bradycardia is associated with any of these symptoms, you should speak with your doctor to determine the cause. Proper treatment can bring your heart rate back.
The risk of dying from bradycardia is relatively low in the absence of symptoms. However, in rare cases, some symptomatic bradycardias can cause cardiac arrest if left untreated.
Of the two common causes of bradycardia (mediated by the sinus node and heart block), sinus node bradycardia is more common.
Sinus node bradycardia
The heartbeat is generally generated and coordinated by an electrical impulse from the heart. This impulse comes from the sinus node, a small nest of cells located in the upper part of the right atrium.
When the sinus node produces these electrical impulses at a relatively low rate, the heart rate becomes slow, resulting in sinus bradycardia.
The causes of sinus bradycardia can be temporary or permanent. Stable causes are likely to require treatment.
- Transient sinus bradycardia – Increased vague tone, such as during sleep, often leads to this type of low heart rate. This nerve helps regulate the functioning of the heart, lungs, and digestive tract. Once the vague tone returns to normal, the heart rate also returns to normal. Therefore, you may not need ongoing treatment for bradycardia itself.
- Persistent sinus bradycardia : Internal sinus disease (disease within the sinus node itself) most of the time it causes a persistent type of sinus bradycardia. Usually, inner sinus disease occurs due to fibrosis (scarring) within the sinus node, which is a common result of aging. Therefore, inner sinus disease usually occurs in people 70 years of age or older.
Internal sinus node disease
People with internal sinus disease may have an abnormally low heart rate. This slowing of the pulse can occur both at rest and during exercise.
People with symptomatic disease often have sick sinus syndrome or sinus node dysfunction. As a result, your heart rate can range from bradycardia to tachycardia (rapid heartbeat).
In addition to internal sinus node disease, sinus bradycardia can be caused by several other conditions, including:
- Cardiac ischemia
- Heart injury from trauma or heart surgery
- Various types of infections, including Lyme disease , Chagas disease and Rocky Mountain spotted fever
- Diseases of the brain, especially those associated with increased intracranial pressure or stroke.
- Hypoxia (low oxygen levels in the blood), which is common with obstructive sleep apnea.
- Various drugs, including beta-blockers , calcium channel blockers , antiarrhythmics , opioids , lithium, and some chemotherapy drugs
The second common type of bradycardia is heart block. Unlike sinus bradycardia, heart block is always abnormal.
Heart block occurs when the heart's electrical impulses are totally or partially blocked as they travel from the heart's atria to the ventricles . Because the sinus node, which generally determines the heart rate, is located in the atrium, the blockage between the atria and the ventricles causes the heart rate to change.
When the heart's ventricles cannot receive information from the sinus node about how fast to beat, they use information from another specific part of the heart between the atria and the ventricles, called the AV node . This communication breakdown leads to potentially dangerous bradycardia.
As with abnormal sinus bradycardia, heart block can be temporary or permanent.
- Transient heart block can occur with certain conditions, such as Lyme disease, thyroid dysfunction , or drug toxicity (especially digitalis, a drug used to treat certain heart conditions). In these cases, treatment of the underlying disease is necessary. Sometimes treatment can include a temporary pacemaker .
- Persistent heart block can be the result of many conditions, including genetics, congenital disorders, sarcoidosis , and amyloidosis. If your doctor suspects a structural disorder such as cardiomyopathy , he or she may recommend imaging with a transthoracic echocardiogram (ultrasound to see the heart in motion). Persistent, mostly symptomatic or complete heart block is more likely to require ongoing treatment. Your doctor may recommend a stress test if you only have symptoms during exercise to see if a pacemaker can help.
- Partial blocks occur when electrical signals to the heart are intermittently delayed or cut off. A complete block occurs when signals are completely cut off and will likely require pacemaker therapy.
Assessment of bradycardia is usually fairly straightforward. But first, your healthcare provider should look at an electrocardiogram (ECG) if you have a slow heart rate. An EKG can help determine if a decrease in heart rate is due to sinus bradycardia or heart block.
Next, the doctor must determine whether the bradycardia will be permanent or temporary (temporary), such as an infection. This determination can often be accomplished simply by looking closely at the medical history.
The tests may include:
- Stress test : For some people (mostly elderly), sinus node disease or heart block can only cause symptoms with exercise. A stress test can help diagnose these cases. This is because it can determine if the heart rate increases appropriately in response to exercise. (Without this, these cases may appear asymptomatic.)
- Long-term ambulatory ECG : With this test, you will perform normal daily activities under supervision. It can also help diagnose bradycardia that occurs intermittently.
- Electrophysiological examination : Specialized cardiac catheterization can be quite accurate in diagnosing sinus node disease and heart block. However, this invasive test is generally not necessary to make a diagnosis.
Treatment for a slow heart rate depends on whether the cause is sinus bradycardia or heart block, and whether it is reversible or not.
You can treat transient sinus bradycardia by avoiding conditions that cause increased vagus nerve tone. For example, treating sleep apnea or taking medication are some of the things that can resolve transient bradycardia.
Persistent bradycardia can also be reversible if due to specific causes, including:
- Drug therapy
In these cases, aggressive treatment of the underlying problem often helps reduce the heart rate.
If sinus bradycardia is reversible or does not cause symptoms, you can usually control it by monitoring it at regular follow-up exams.
When heart block or sinus node dysfunction causes bradycardia and causes no symptoms, your doctor may recommend a permanent pacemaker .
In some cases, doctors try a temporary pacemaker. For example, if a partial atrioventricular block is caused by a myocardial infarction ( heart attack ), the use of a temporary pacemaker can help doctors determine whether the block is permanent or reversible.
Bradycardia (low heart rate) is usually normal. It doesn't always cause illness, but it can. Sinus bradycardia, which causes symptoms and heart block, whether present or not, should be evaluated by a doctor. These conditions may require treatment, such as a pacemaker.
Get the word of drug information
If your heart rate is low, you may be concerned. Rest assured, for many people, bradycardia is a normal heart rate. However, in other cases, it can be a sign of a medical condition that requires treatment. So if you experience symptoms like dizziness, fatigue, fainting, shortness of breath, or chest pain, be sure to rate them.
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