Complete atrioventricular block of a permanent or intermittent type is a relatively uncommon alteration of conduction. It may develop in the course of acute rheumatic fever and diphtheria. It is most commonly found in elderly persons in association with serious forms of chronic heart disease, usually of a coronary arteriosclerotic type, with or without aortic valvular heart disease. The arrhythmia may also occur in association with congenital heart disease, syphilitic heart disease, and neoplasm. Rarely it appears as a complication of digitalis therapy.
A reflex vagal mechanism as is present in the hyperactive carotid sinus syndrome may account for complete heart block, and this variety is ordinarily evanescent. In episodes of supraventricular tachycardia, atrial flutter, and atrial fibrillation, exhaustion of the conduction system presumably occurs, often resulting in complete atrioventricular dissociation.
When atherosclerosis is the cause of complete block it is usually the right coronary artery which is involved, since