Atrioventricular block. Mechanism, clinical presentation, and therapy

Over the last decade or so our understanding of the mechanism and pathophysiology of atrioventricular (AV) block has been enhanced considerably. This rapid progress has occurred through the widespread application of the electrode catheter technique for His bundle recording in humans. According to a recent survey of cardiac pacing in this country, 117,800 new pacemakers are implanted each year. Since 1978 the yearly rate of new implants has grown from 309 to 513 per million population. Although in recent years the sick sinus syndrome forms a larger segment of the pacemaker population, symptomatic AV block still constitutes one of the major indications for permanent pacing. Thus the understanding of the mechanism, clinical presentation, and therapy of the different types of AV block is of importance not only to the practicing cardiologist but to the internist as well. In this article we will review the mechanism of AV block and bifascicular block, the role of His bundle electrocardiography in localizing the site of AV block, and the therapy of the different types of AV block. AV blocks have been classified into four types: first-degree, second-degree, high-degree, and third-degree (or complete) heart block.