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 small fibers that go into the muscle of the heart. The nodes, bundles, and fibers are responsible to keep the heart muscles beating all together and at the correct rate.
A defect along any of these pathways can cause a heart block. This doesmean 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. First-degree heart block. This type occurs when the electrical impulse passes through the heart slower than normal, but heartbeat and rhythm are still within a healthy range. This type of block does not mean there is anything seriously wrong with the heart.Second-degree heart block. This occurs when some of the electrical signals from the upper chamber of the heart, called the atrium, fail to reach the lower chamber of the heart, called the ventricle. This results in what are called "dropped beats."Complete heart block.This is the most serious type of heart block. In this condition, no electrical impulses pass from the upper to the lower parts of the heart. The lower part starts beating on its own, but at a much slower rate than normal. This heart rate may be too slow and irregular to maintain an adequate blood supply to the vital organs.
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 will appear. The person may feel dizzy, weak, confused, or may have less tolerance for exercise. Sometimes, a person may pass out or even suffer a stroke, heart attack, or sudden cardiac arrest.
Many times, heart block is a symptom that the person has another type of heart disease. Heart blocks are common in people who have: history of heart attackscoronary artery diseaseinfectious diseases of the heart, such as endocarditishereditary defect of the heart, called congenital heart block
Certain medicines can also cause heart block if the levels in the body build up too much. Some examples include: beta blockers, such as propranolol (i.e., Inderal), metoprolol (i.e., Lopressor, Toprol) or pindolol (i.e., Visken)calcium channel blockers, such as verapamil (i.e., Calan, Isoptin, Verelan) or diltiazem (i.e., Cardiazem, Cartia, Dilacor)digitalis glycosides, such as digoxin (i.e., Lanoxin, Lanoxicap)
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 is likely to be more serious and alerts the healthcare provider to a new or worsening underlying heart condition.
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.
An electrocardiogram, (called ECG), 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.
The long-term effects of heart block depend on the underlying heart disease. If the underlying disease causes a fixed slow heart rate, less than 45 beats/minute, then a pacemaker will be needed. Otherwise, the heart block in and of itself is not a major concern so long as the underlying disease is stable.
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 and the more sever the symptoms.
Heart block causes no risk to others.
Many times heart blocks are not treated at all. Treatment of other heart problems reduces the risk that the block will become more severe. In some cases, 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 increase the heart rate. The healthcare provider may substitute a different medicine when the block is the result of a medication side effect.
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. Each medicine used to treat heart disease has its own side effects.
Once a pacemaker is implanted, the healthcare provider monitors the person's heart rate at each office visit. Medicine for existing heart disease may also need to be adjusted periodically. With the correct treatment, most people are able to continue with their regular activities.
Regular visits to the healthcare provider 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.
Merck Manual, 1999
Harrison's : Principles of Internal Medicine,1991
Current Medical Diagnosis and Treatment, 1996