Each heartbeat begins with an electrical impulse that signals certain areas of the heart to contract. These contractions open valves and push blood through each chamber as the blood flows in a cycle: body-heart-lungs-heart-body. When a person is born with a congenital defect, one or more parts of the heart usually do not function correctly. A non-functional valve or malformed section of the heart can alter the heart's rhythm.
Each heartbeat begins in a specialized area of the right atrium called the sinus node. The sinus node starts each heartbeat by generating a small amount of electricity, which spreads into the muscle cells of the atria. This causes these upper chambers to contract. If a chamber is malformed by congenital heart disease, it may cause irregularity.
Next, the electrical activity moves into the junction between the atria and ventricles. (The ventricles are the heart's main pumping chambers.) This area is called the atrioventricular node or A-V node. The A-V node acts as a relay station. It takes the signal coming from the atria, delays it slightly, then passes it into the ventricles, which causes them to beat. When the ventricles beat, they pump blood throughout the body. This creates a pulse that can be felt at several places in the body. Again, if valves or ventricles are affect by a defect, it can affect the heart's ability to pump blood throughout the body effectively.
Patients with underlying problems in the function and structure of the heart are more prone to heart rhythm problems. As patients who've had successful heart surgery live longer, doctors are diagnosing more heart rhythm abnormalities among survivors.
A heart rhythm abnormality is evaluated in ways much like those used to evaluate other health problems. The history of your symptoms, including sensation of your heart beating fast, dizziness and fainting are very important.
Your doctor can use several tests to diagnose an arrhythmia. The first is usually an electrocardiogram (ECG or EKG). An ECG machine records your heart's electrical activity. The tracings can be recorded on paper or a computer disk. However, EKGs are only a brief snapshot of your heart rhythm and may not detect the actual arrhythmia.
Normally, heart rate varies depending on the person's age and activity. The term "arrhythmia" refers to abnormally fast or slow heart rates and to irregular heart rhythms. Arrhythmias are usually diagnosed with an electrocardiogram (ECG).
A heart rate that's faster than normal is called tachycardia. Tachycardia may reduce the heart's pumping ability and may require treatment. Sometimes tachycardia is due to an abnormality of the heart's electrical circuits, while other times it may be due to abnormally high adrenaline levels as seen, for example, after surgery.
Medications known as beta-blockers such as propranolol or atenolol are used to prevent the tachycardia or, at a minimum, slow down the heart rate to prevent symptoms or problems. Digoxin may also be used to prevent certain kinds of tachycardias.
A heart rate that's slower than normal is called bradycardia. Bradycardia may be associated with certain congenital heart defects or may develop by itself before birth or after heart surgery. In some more serious cases and/or if the heart rate is very slow, an artificial pacemaker may be needed.
Irregular beats or early (premature) heartbeats are often seen in normal infants and children. They may be related to a congenital heart defect or may occur after surgery. Irregular heartbeats without serious fast or slow rhythms usually don't need treatment.
The tests used to diagnose arrhythmias include exercise testing, Holter monitoring, event recorders and electrophysiologic studies.