What causes heart block?
Heart block has a variety of causes. It can sometimes be a result of a congenital defect. It can also occur after a heart attack or as a result of myocarditis (inflammation of the heart muscle), cardiomyopathy (a disorder of the heart muscle) and other types of heart disease. Although these conditions are more common in older people, young people can also be affected. Heart block may also occur after heart surgery and in this case may be either temporary or permanent. Wenckebach block
may occur as a result of taking too much digoxin, or can occur after a heart attack. Heart block may be caused by coronary artery disease, inflammation of the heart muscle, rheumatic fever, or overdose of certain heart drugs. Treatment depends on the degree of heart block experienced. Some cases need no treatment while others require medication or an artificial pacemakers.
The electrical activity of the heart starts in the sinoatrial (SA) node in the atrium and travels through the atrioventricular (AV) node to reach the ventricles. The AV node is supplied by two different parts of the nervous system - the parasympathetic and sympathetic. These are both parts of the autonomic nervous system - which controls involuntary actions in the body. The sympathetic nervous system has nerves distributed to the heart, blood vessels, lungs, intestines and other organs in the abdomen. It governs functions in these areas by reflex action in balance with the parasympathetic nervous system, which supplies the same areas, but often provides the opposite function to the sympathetic nervous system. The AV node is sensitive to what is called autonomic tone - the action of the two branches of the autonomic nervous system together. Heart block may occur at any point along this electrical pathway. Heart block of the AV node can be of several types, and a doctor generally can diagnose these by looking at the patient's electrocardiogram (ECG, EKG).
There are two uncommon muscular degenerative diseases which are responsible for isolated heart block in adults - Lev's disease and Lenegre's disease. Hypertension (high blood pressure) and stenosis (tightening) of the aortic and mitral valves of the heart are specific disorders which will accelerate degeneration of the conducting system or cause the deposition of calcium or fibrosis of the system.