A slow heartbeat is called bradycardia and is defined as a heart rate that is slower than healthy levels. In most adults, the heart beats at least 60 times per minute. Faster, age-related heart rates are considered healthy in children.
When a person is at rest, the heart normally beats at a rate that is within a relatively narrow range. This range is usually 60 to 100 beats per minute in adults, slightly faster in children, and somewhat slower in trained athletes.
With certain conditions, however, the heart rate may decrease below a healthy range. When the heart beats lower than the healthy range, the body may not get all the blood it needs to work correctly. This can affect a person's overall health and energy levels.
A person with a slow heartbeat may have no symptoms at all. When symptoms do occur, they may include: chest painexcessive sweatingfatigue or weaknesslightheadedness or dizzinesspalpitations, which are an unusual awareness of the heartbeatpassing out or faintingshortness of breathother symptoms related to the cause
There are many possible causes of a slow heartbeat, including: arrhythmias, which are irregular heartbeats caused either by abnormalities in the electrical conduction system of the heart, by damage to the heart muscle, or by salt imbalances, particularly low potassiumcertain medicines, such as atenolol (i.e., Tenormin) and diltiazem (i.e., Cardizem, Cartia XT, Dilacor XR, Dilt-CD, Diltia XT, Taztia XT, Tiazac), commonly used to treat high blood pressure, or digoxin (i.e., Lanoxin), commonly used to treat congestive heart failureheroin overdosehypothyroidism, that is, a low level of thyroid hormone in the bodyserious head injuries or brain damage, which can lead to a condition called increased intracranial pressureshock, a serious condition in which there is poor blood circulation. If this is left untreated, it can result in death
Regular exercise can also result in a slow heartbeat. This happens because the exercise has actually strengthened the heart to the point where it can beat less often and still perform its job effectively. In this case, the slow heartbeat is not a cause for concern.
Other causes are also possible. Sometimes no cause can be found.
Most cases cannot be prevented. Medicines should be taken exactly as prescribed. The doses should not be more than the healthcare professional has prescribed. Avoiding heroin could prevent cases due to heroin overdose.
The speed of the heartbeat can usually be measured by checking the pulse or listening to the heartbeat with a stethoscope. The healthcare professional needs to determine the cause of the a slow heartbeat. Sometimes it is obvious from the history and physical exam. In other cases, further tests may be needed.
For example, an electrocardiogram (ECG), can help diagnose irregular heartbeats and heart attacks. A series of blood tests known as thyroid function tests can be used to diagnose low thyroid levels. A drug test of the urine or blood can be used to diagnose heroin use. A special X-ray test called a cranial CT scan may be done to look for head injuries or brain damage.
If the heart beats too slowly, it may not be able to pump blood well enough to keep a person alive. Most long-term effects are related to the cause. For example, cases due to hypothyroidism often go away quickly with treatment, and there are no long-term effects. Cases due to an arrhythmia or shock sometimes result in death. Head injuries and brain damage may cause permanent disabilities.
A slow heartbeat is not contagious and poses no risks to others.
Treatment is directed at the cause. For example, a person with hypothyroidism is given thyroid hormone pills. Salt imbalances need to be corrected. Someone with arrhythmias may need a pacemaker, which is a device inserted under the skin to control the heart rate using an electrical impulse. A person with head injuries may need surgery or medicines to decrease the pressure inside the skull.
Side effects are related to the treatments. For example, if the dose of thyroid medicine is too high, the person may develop a heart rate that is too fast. Insertion of a pacemaker requires minor surgery, which may result in bleeding or infection.
What happens after treatment depends on the cause of the slow heart rate. A person who has a slow heartbeat because he or she is a good athlete needs no treatment. An individual taking thyroid or blood pressure medicines usually needs further monitoring and treatment for life. Someone with head injuries or brain damage may need help with regular activities.
The speed of the heartbeat can be monitored closely if needed. This is done with special equipment that measures the electrical activity in the heart. Other monitoring is related to the cause. For example, an individual who has had a heart attack may need close monitoring in the intensive care unit. Any new or worsening symptoms should always be reported to the healthcare professional.
Harrison's Principles of Internal Medicine, 1998, Fauci et al.