Heart block is a disruption in the relay of electrical signals that control activity of the heart muscle.
The heart beats by using electric impulses. These impulses follow a specific route through the heart. These routes or pathways are sometimes grouped together into specialized areas called nodes and bundles.
Bundles send out little fibers that go into the muscle of the heart. The nodes, bundles, and fibers are responsible for the unified beating of the heart and the rate at which it beats. A defect along any of these pathways can cause a heart block. This does not mean the blood flow or blood vessels are blocked.
There are many kinds of heart block. Each type depends on where the damage has occurred in the electrical pathway.
Many times, heart block is a symptom that the person has another type of heart disease. Heart blocks are common in people who have:
Certain medicines can also cause heart block if the levels in the body build up too much. Some examples include:
Highly-trained athletes may also have the less severe forms of heart block, but will most likely have no symptoms other than a slow heartbeat.
A block that has existed for a long time may pose no problem. A block that appears suddenly may be due to a new heart problem or the worsening of an old one. A change in the heart block can alert the doctor to a change in the status of the heart.
Symptoms depend on how severe the heart block is and in what part of the heart it occurs. Often, heart block causes no symptoms. If the heart block is severe enough, the heart rate will slow, and symptoms of low blood pressure or stroke will appear. The person may feel dizzy, weak, confused, or may have less tolerance for exercise. At times, some people may even pass out.
An electrocardiogram, which is a test also called ECG or EKG, can diagnose the disorder. Heart blocks often have a certain pattern that the ECG machine traces on special paper. In some cases, special tests using probes placed into the heart can measure the flow and direction of electricity.
Treatment of an existing heart problem can make heart blocks less likely to develop or worsen. Avoiding medicines that cause heart block may also help in some people. There is no way to prevent a heart block from occurring in a healthy person.
The long-term effects of heart block depend on the underlying heart disease. Heart block is a sign of the disease process. If the underlying disease causes a fixed slow heart rate, less than 45 beats/minute, then a pacemaker will be needed. If the underlying disease does not get worse, then the heart block is not a concern. If a new heart block appears suddenly where there was none before, it can result in a heart attack.
In summary, the worse the underlying disease the worse the block. The worse the block, the slower the heart rate. The slower the rate, the worse the symptoms. Common symptoms are:
Heart block causes no risk to others.
Many times heart blocks are not treated at all. Treatment of other heart problems reduces the risk of the block getting worse.
In some cases, the block becomes so severe that heart can no longer beat fast enough to keep the body healthy. When this occurs, an electrical device called a pacemaker can be used to help the heart beat at a healthy rate. Medicines can also be used to help restore the heart rate. Or, the doctor may substitute a different medicine when the block is the result of a side effect from a certain type of medicine.
Pacemakers use batteries to work. These batteries can last for years, but will need to be replaced at some point. The pacemaker itself may also need replacing after years of use. The side effects of medicines used to treat heart disease vary, depending on the medicine.
Once a pacemaker is implanted, the doctor will monitor the person's heart rate with each office visit. Medicine for existing heart disease may also need to be adjusted from time to time. With the correct treatment, most people are able to continue with their regular activities.
Regular visits to the doctor and repeat ECG testing, sometimes by telephone, helps pick up any changes in the heart's status. Any new or worsening symptoms should be reported to the doctor.
Author:Eric Berlin, MD
Editor:Crist, Gayle P., MS, BA
Reviewer:Kathleen A. MacNaughton, RN, BSN
Merck Manual, 1999
Harrison's : Principles of Internal Medicine,1991
Current Medical Diagnosis and Treatment, 1996