What is heart block?
Heart block is an abnormal heart rhythm that usually results in a slow heart rate. It is caused by a problem in the heart’s electrical system, also called the conduction system. When a child has heart block, the electrical impulse is delayed or blocked completely as it travels from the heart’s upper chambers (the atria) to the heart’s lower chambers (the ventricles). There are three different types of heart block called first degree, second degree, and third degree heart block.
Heart block occurs at the level of the AV node. (Click here to learn more about the normal heart rhythm). In first degree heart block, the impulse is slowed but does reach the ventricles — resulting in a normal heart rate. In second degree heart block, some of the impulses are blocked while others get through so the heart rate is often slower than normal and irregular. In third degree heart block (complete heart block) none of the impulses from the upper chambers are able to reach the lower chambers. Nearly all patients with complete heart block have what is called an escape rhythm. An escape rhythm comes from the heart’s lower chambers and provides a slow heart rate, usually between 40 and 60 beats a minute.
The most common type of heart block is third degree heart block. This is also called complete heart block or complete atrioventricular heart block. It can be present at birth or it can occur later in life. If present at birth it is called congenital heart block. Overall, this is very rare but occurs more often if the mother has a disease called lupus erythromatosis. It is also more common in infants born with a rare heart defect called corrected transposition of the great arteries.
Complete heart block can also occur after heart surgery. There is a greater risk of heart block when the surgery involves areas that are close to the normal conduction system. These operations include repair of subaortic stenosis, VSD repair, and mitral valve repair. Complete heart block can also be a complication of a heart infection such as myocarditis.
How does this problem affect my child's health?
Children born with heart block who have an otherwise normal heart usually do very well even though their heart rates may be quite slow. Most of these children have good energy levels and grow and develop normally. In children with very slow heart rates (e.g. less than 45 to 50 beats per minute, long pauses between heart beats, low energy, or fainting a pacemaker may be needed).
How is the problem treated?
If the child has surgical heart block or symptoms from having too low a heart rate, the primary treatment is pacemaker implantation.
Care and services for patients with this problem are provided in the Pacemaker Clinic, Arrhythmia Clinic and Congenital Heart Clinics at the University of Michigan Medical Center in Ann Arbor.
What are the long-term health issues for these children?
Overall the outlook for children with heart block is very good. As described above, the main treatment is placement of a pacemaker. Pacemakers are safe and effective and require few changes in lifestyle.
Exercise guidelines: Exercise guidelines are best made by a patient’s doctor so that all relevant factors can be included. For patients with congenital heart block, there are usually no activity restrictions required although the person should be in a position to self-limit their activities if symptoms develop. After pacemaker implantation, most doctors restrict participation in contact sports. For patients with other heart problems in addition to heart block, exercise restrictions must be individualized.
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Reviewed by: Gerald Serwer, MD
Reviewed September, 2012