The heart has two upper receiving chambers, called atria, and two lower pumping chambers, called ventricles. The heart also has a built-in electrical system that controls and coordinates its pumping function.
A heartbeat is caused by an electrical impulse traveling through an intricate system of electrical pathways in the cells of the heart tissue. The impulse travels through the upper and then lower chambers, causing the contraction and relaxation that results in pumping of blood.
The impulse originates in the sinus (sinoatrial, or S-A) node, the heart’s natural pacemaker located within muscle at the top of the right upper atrium, and travels across both atria. Then the impulse collects, or pauses, in the atrioventricular (A-V) node, located within muscle near the center of the heart, and travels down the ventricles. The A-V node is the only normal electrical connection between the atria and the ventricles. At 3 to 4 millimeters, the sinus and A-V nodes are tiny, the size of a few grains of sugar.
Heart block occurs when there is a delay in the conduction of the electrical impulse through the heart. In most cases, heart block is caused by a problem with the A-V node. There are several types of heart block, including:
- Complete heart block: The most common type of heart block in children is complete heart block, also called third-degree heart block. In complete heart block, the electrical impulse never gets past the A-V node. The only reason a person can survive is that another, weaker natural pacemaker takes over in the ventricles. The ventricles are able to pump blood out to the body, but more slowly than normal.
- Congenital complete A-V block: Sometimes children are born with complete heart block (this is called congenital complete A-V block). In some of these cases, the child also has a severe structural heart defect, such as heterotaxy or congenitally corrected transposition of the great arteries. In other cases, congenital heart block occurs because the mother has an autoimmune disorder, such as systemic lupus erythematosus.
- Acquired complete heart block: Sometimes complete heart block in children is acquired. Causes of acquired complete heart block include: diseases, such as myocarditis, which scar and damage heart tissue; heart surgery and certain medications.
- First-degree heart block: In first-degree heart block, the electrical impulses move through the A-V node more slowly than usual.
- Second-degree heart block: In second-degree heart block, there is a delay in the electrical impulse reaching the ventricles. Skipped heartbeats and a slower-than-normal heart rate may result. There are two types of second-degree heart block. In some cases, second-degree heart block will eventually progress to complete heart block.
- Bundle branch block: There is a flaw in the bundle branches, the pathways for the electrical impulse running along the right and left ventricles. This can be congenital or acquired, and is often seen after surgery to close a defect in the septum (the wall of tissue) between the ventricles.
Symptoms of complete heart block can include:
- Fainting (syncope)
- Shortness of breath
- Palpitations or skipped heartbeats
- Exercise intolerance
The other types of heart block in children can also cause these symptoms, though they are usually less severe.
In infants born with complete heart block, symptoms can also include:
- Blue or purple tint to the skin (cyanosis)
- Lethargy (the baby seems “out of it”)
- Fatigue with feeds
Sometimes heart block may not cause any symptoms. In rare cases, complete heart block or second-degree heart block can cause sudden death, even in a person with few or no symptoms.
Sometimes complete heart block is diagnosed prenatally. With fetal echocardiography, doctors may notice a difference between the rate at which the upper and the lower chambers are beating.
The Fetal Heart Program at Children’s Hospital can monitor baby and mother throughout the pregnancy and create a plan for labor and care after the birth. CHOP has its own delivery unit, on the same floor as cardiac operating rooms and cardiac patient care units. Babies born with complete heart block can have wires for a temporary pacemaker placed within minutes. The Fetal Heart Program team will discuss delivery in the Garbose Family Special Delivery Unit with mother and family.
In other cases, heart block in children is not diagnosed until a later age, or even adulthood. Diagnosis of heart block may require some or all of these tests:
- Electrocardiogram (ECG or EKG): a record of the electrical activity of the heart
- Holter monitor: a continuous measurement of the heart rate and electrical activity for 24 hours, or more
- Echocardiogram: sound waves create an image of the heart
In many cases, complete heart block will eventually require a pacemaker. This is a battery-operated device that doctors implant under the skin. Leads (wires) attached to the device are placed on the surface of the heart (in infants), or are threaded through veins directly into the heart (in older children and teenagers). The pacemaker wires serve as replacement sinus and A-V nodes, and the electrical signals they send reach both the atria and the ventricles, correcting the heart block.
Implanting and maintaining a pacemaker comes with some risk; doctors factor this into their decision about what treatment to pursue. Doctors will carefully monitor these patients so they know if there is a change in the patient’s condition and a pacemaker should be placed.
In some cases of complete heart block, the heart rate is sufficient and a pacemaker won’t be necessary. Rarely, second-degree heart block will require a pacemaker. First-degree heart block and bundle branch block usually don’t require any treatment.
Children with complete heart block will require lifelong care by a cardiologist. Those with the less severe forms of heart block should also continue to see a cardiologist regularly.
Children with pacemakers will need to visit an electrophysiologist, a doctor who specializes in problems with the electrical system of the heart, once or twice a year, and will also need routine monthly testing of their pacemaker by telephone. Children with pacemakers can lead physically active and healthy lives. However, some sports and activities may not be allowed.
As a group, children with complex congenital heart defects who have had open heart surgery as infants are at a higher risk for neurodevelopmental issues when compared to children without congenital heart defects. The Cardiac Center at CHOP created the Cardiac Kids Developmental Follow-up Program to provide evaluation, screening and clinical care for children with complex congenital heart disease who are at risk for neurodevelopmental problems.
In addition, our pediatric cardiologists follow patients until they are young adults. We will help with the transition to an adult cardiologist. The Philadelphia Adult Congenital Heart Center, a joint program of Children's Hospital of Philadelphia and the University of Pennsylvania, meets the unique needs of adults who were born with heart defects.