What is a third degree heart block?

A third-degree heart block, also known as complete heart block, is a condition where the electrical impulses responsible for regulating the heartbeat are completely blocked from the atria (the upper chambers of the heart) to the ventricles (the lower chambers). This blockage prevents the atria and ventricles from beating in a coordinated manner, which can significantly affect the heart's ability to pump blood effectively throughout the body. In a healthy heart, electrical signals are generated by a natural pacemaker called the sinoatrial (SA) node, located in the right atrium. These signals then travel through the atria causing them to contract and push blood into the ventricles. After that, the signals reach the atrioventricular (AV) node, which is the heart's natural backup pacemaker. The AV node delays the signal slightly before sending it to the ventricles, allowing them to contract and pump blood out to the body. However, in a third-degree heart block, the electrical signals do not pass through the AV node properly. This can be due to various reasons, including congenital heart defects, certain heart diseases, or damage to the heart's conduction system from conditions like coronary ischemia and myocardial infarction. When the blood flow to the heart muscle is reduced or lost, the conduction system can be damaged, leading to this block. The treatment for third-degree heart block often involves the use of a pacemaker, a small device that sends electrical impulses to the heart to maintain a normal heart rhythm.

The most common cause of complete block in adults is coronary ischemia and myocardial infarction. Reduced blood flow or complete loss of blood flow to the myocardium damages the conduction system of the heart, and this results in an inability to conduct impulses from the atrium to the ventricles.