Complete, or third degree, heart block is a condition whereby no electrical signals from the top part of the heart, the atria, reach the bottom chambers of the heart, the ventricles. Thus, the ventricles must generate their own electrical pacemaker impulse. However, the electrical impulse is much slower than the regular heartbeat, according to the Mayo Clinic. This can lead to a failure of the heart to pump blood to the organs of the body and sudden cardiac death. Complete heart block can be caused by many different disorders. Determining the cause of the heart block helps physicians choose the best treatment.
Congenital Heart Block
In rare cases, third degree heart block can be present at birth, reports Drugs.com. A heart block that is present at birth is called congenital heart block. The heart block is usually caused by a structural defect in the cells of the heart that control the heart rate. Patients will often present with a significantly decreased heart rate that is unexplained by any other conditions. The patients will also have abnormal reading on the electrocardiogram, or ECG, which is a test that measures the electrical activity of the heart.
Heart Damage
Damage to the heart muscles can be a cause of complete heart block, states the American Heart Association. The heart can be damaged by a heart attack, atherosclerosis, or damage during heart surgery. In order to cause heart block, the cells of the heart that are supposed to control the heart rate must become damaged. This includes the AV node, bundle branches, and the bundle of His. All three of these tissues aid in producing the electrical pacemaker potential of the heart. Once these areas of the heart become injured, the patient can develop third degree heart block.
Medication
There are certain medications that can cause complete heart block, according to the Mayo Clinic. These drugs can inhibit the conduction of electricity in the heart by preventing the proper flow of electrolytes such as potassium, calcium, and sodium. Without these electrolytes, the heart is unable to properly produce and propagate the signal needed to keep the heart beating normally. Drugs that can cause third degree heart block include amiodarone, qunidine, flecainide, and procainamide.
