AVblock

AV block, or atrioventricular block, is a form of heart block in which conduction from the atria to the ventricles through the AV node and His-Purkinje system is impaired. It is categorized by the degree of electrical interruption: first-degree AV block (prolonged PR interval with all atrial impulses conducted), second-degree AV block Mobitz type I (Wenckebach; progressively lengthening PR with intermittent nonconducted impulses), second-degree AV block Mobitz type II (sudden, fixed PR with dropped beats), and third-degree or complete AV block (no atrial impulses conduct to the ventricles, leading to AV dissociation).

Causes are diverse and can include ischemic heart disease or myocardial infarction, cardiomyopathy, degenerative conduction-system disease, congenital AV block, infiltrative or inflammatory diseases, electrolyte disturbances, and medications that slow AV nodal conduction (such as beta-blockers, calcium channel blockers, and digoxin). Surgical injury to the conduction system and certain autoimmune conditions can also produce AV block.

Symptoms range from none to significant bradycardia with dizziness, syncope, fatigue, or heart failure symptoms. Diagnosis is primarily based on ECG findings, which distinguish the different AV block types. Additional testing may include Holter monitoring, event recorders, echocardiography, and evaluation for reversible causes or underlying structural disease.

Management depends on the block type and symptoms. First-degree AV block and many asymptomatic cases may require observation and treatment of underlying conditions. Mobitz II and complete AV block often require temporary pacing in the hospital and usually permanent pacemaker implantation, typically a dual-chamber device, to restore synchrony between atrial and ventricular contraction. Reversible causes should be addressed, and in acute MI, reperfusion therapy is essential. Prognosis varies with the cause and the presence of symptoms.