Definition Heart block is a disruption in the transmission of electrical signals between the upper and lower chambers of the heart.
What is going on in the body? The heart beats by using electric circuits. These circuits allow the electricity to follow a specific route through the heart. These electric routes or pathways are sometimes grouped together into specialised areas called nodes and bundles.
Bundles send out little fibres that go into the muscle of the heart. The nodes, bundles, and fibres 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.
There are many kinds of heart block. Each type depends on where the damage has occurred in the electrical pathway.
The worst form of heart block is called complete heart block. In this condition, the upper and lower parts of the heart beat separately. When this occurs, the lower part of the heart beats so slowly that it cannot keep blood flowing to the vital organs.
What are the signs and symptoms of the disease? Often, heart block causes no symptoms. If the heart block is severe enough, though, the heart rate will slow and symptoms of low blood pressure or stroke will appear. The person may feel dizzy, weak or confused and, occasionally, may lose consciousness.
What are the causes and risks of the disease? Many times, a heart block is a symptom that the person has another type of heart disease. Heart blocks commonly occur in people who have:
infectious diseases of the heart, such as endocarditis
Well-trained athletes and people who take certain medications that may cause this problem as a side effect also may have heart blocks. A block that has existed for a long time may pose no problem. A block that appears suddenly may be associated with a new heart problem or worsening of an existing one. A change in the heart block can alert the doctor to a change in the condition of the heart.
What can be done to prevent the disease? Treatment of an existing heart problem can make heart blocks less likely to develop or worsen. There is no way to prevent a heart block from occurring in a healthy person.
How is the disease diagnosed? A test called an electrocardiogram, or ECG, can diagnose the disorder. Heart blocks often have a certain pattern that the ECG machine traces on special paper. In some instances, special tests using probes placed into the heart can measure the flow and direction of electricity.
What are the long-term effects of the disease? The long-term effects of heart block depend on the underlying heart disease. Heart block is an indicator of the disease process. If the underlying disease causes a fixed slow heart rate, less than 45beats/min, than a pacemaker will be necessary. If the underlying disease does not get worse, then the heart block is of no real importance. If a new heart block appears suddenly where none existed before it can indicate 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. These symptoms are:
What are the risks to others? Heart block causes no risk to others.
What are the treatments for the disease? 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 at the proper pace. When this occurs, an electrical device called a pacemaker can be used to help the heart beat at the proper rate. Medications can also be used to help restore the heart rate.
What are the side effects of the treatments? Pacemakers use batteries to work. These batteries can last for years, but will need to be replaced. The pacemaker itself may need replacing after years of use. The side effects of medication to treat existing heart disease varies depending on the drug.
What happens after treatment for the disease? If a pacemaker is implanted, the doctor will monitor the person's heart rate afterward. Medication for existing heart disease may also need to be adjusted.
How is the disease monitored? Regular visits to the doctor and repeat ECG testing, sometimes by telephone, helps the doctor watch for any changes in the heart's status.
Author: Eric Berlin, MD Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
