The heartbeat is created by an electrical signal that starts in the heart’s upper right chamber (right atrium). The signal is produced in an area of specialized cells in the atrium called the sinus node.
The electrical signal moves down through the heart to the atrioventricular (AV) node, another cluster of specialized cells that is located in the center of the heart between the atria and ventricles.
The AV node is sometimes referred to as an electrical relay station because its function is to slow the electrical current before it passes to the lower chambers of the heart (ventricles).
From the AV node, the electrical current travels to the ventricles along special fibers embedded in the heart walls.
When the current arrives in the ventricles, they contract and pump blood out to the body.
In people with heart block, also called AV block, the electrical signal that controls the heartbeat is partially or completely blocked from reaching the ventricles.
Who is at risk for heart block?
Heart block can be present at birth (congenital), but most heart block develops after birth. In general, the risk of acquired heart block increases with age, along with the incidence of heart disease.
First-degree heart block is common among well-trained athletes, teenagers, young adults, and people with a highly active vagus nerve.
People with a variety of heart disease, including coronary artery disease, rheumatic heart disease, sarcoidosis or other structural heart disorders, are also at risk for developing first-degree heart block.
What causes acquired heart block?
Acquired heart block has many possible causes, including heart attack (the most common cause), heart disease, an enlarged heart (cardiomyopathy), heart failure and rheumatic fever.
Sometimes heart block occurs as a result of injury to the heart during open heart surgery, as a side effect of some drugs, or after exposure to a toxin.
Treating heart block
Heart block doesn’t always need to be treated, unless the symptoms are serious. However, acquired heart block usually needs treatment.
Transcutaneous pacing (TCP) is a temporary method of pacing the heart. Pads are applied to your chest and electrical pulses are passed through them to stabilise your heartbeat and restore your heart rate to normal.
Once your heartbeat has been stabilised, a permanent pacemaker may be recommended.
Pacemakers are small battery-operated devices that are inserted under the skin of your chest. It sends frequent electrical pulses to keep your heart beating regularly.
Treatment for heart block usually works well if it’s given when required. Deaths caused by heart block are rare.
If a pregnant woman has an autoimmune condition, such as lupus, her unborn baby may develop congenital heart block. Congenital heart defects can also cause heart block.
However, congenital third degree heart block is rare, occurring in one in every 20,000 births.
Acquired heart block can affect people of all ages, but older people are more at risk because the risk factors are more common with age.
For example, your risk of developing heart block is increased if you have a history of heart disease, heart attacks or heart failure.
Elite athletes are at increased risk of developing first-degree heart block. This is because their hearts are often enlarged which can cause mild disruption to the heart’s electrical signals.
Taking certain medications, such as beta-blockers for treating high blood pressure, can also sometimes cause heart block.