What is the most common cause of complete heart block?

Most Common Cause of Complete Heart Block

The most common cause of complete heart block is idiopathic degenerative fibrosis of the cardiac conduction system (Lenegre-Lev disease), particularly in elderly patients, representing a progressive age-related degeneration of the His-Purkinje system. 1

Primary Etiologic Framework

The etiology of complete heart block varies significantly by age and clinical context:

In Elderly Patients (Most Common Overall)

• Degenerative conduction system disease is the predominant cause, occurring as senescence of the specialized conduction tissues 1
• This degenerative process affects the His-Purkinje system progressively and is the same pathophysiologic mechanism responsible for bifascicular block progression 1
• The fibrotic process often coexists with sinus node dysfunction, creating the substrate for both bradyarrhythmias and atrial arrhythmias 1

In Acute Settings

• Acute myocardial infarction is the most common acute cause, with complete heart block developing in approximately 8% of post-MI patients 2
• Up to 1 in 5 patients develop some form of conduction disturbance after MI, making ischemic heart disease a leading acute etiology 2
• Inferior MI typically causes AV nodal block (better prognosis), while anterior MI with His-Purkinje involvement carries unfavorable prognosis with higher mortality 1

In Young and Middle-Aged Adults

• Congenital complete heart block is most common in younger patients without acquired disease 3
• Lenegre-Lev disease (idiopathic degenerative scleroatrophy) can present earlier in life as an inherited condition, sometimes linked to SCN5A mutations 4, 3
• Other causes include autoimmune disorders (systemic lupus erythematosus, rheumatoid arthritis), infiltrative diseases, and congenital structural abnormalities 3, 5

Secondary and Reversible Causes

Infectious Etiologies

• Lyme disease (Borrelia burgdorferi) causes AV block in 0.3-8% of infected patients, though persistent heart block is rare and usually self-limiting with antibiotics 1
• Chagas disease commonly causes conduction defects with progression to complete heart block in endemic areas 1
• Infective endocarditis with perivalvular abscess, particularly aortic valve involvement, can erode into the septum and disrupt the conduction system—new-onset heart block is highly specific for abscess formation 1

Drug-Induced and Metabolic

• Essential long-term drug therapy (beta-blockers, calcium channel blockers, antiarrhythmics) can necessitate pacing when no acceptable alternative exists 1
• Electrolyte disturbances and endocrinologic abnormalities (hypothyroidism) are reversible causes 2, 3

Infiltrative and Inflammatory

• Sarcoidosis causes conduction abnormalities through granulomatous infiltration 4, 5
• Acute rheumatic fever causes PR prolongation commonly, but complete heart block is rare 1, 5
• Myocarditis from various causes (viral, autoimmune, hypersensitivity) can produce transient or permanent block 2, 3

Critical Clinical Pitfalls

Do not assume bifascicular block will progress rapidly to complete heart block—the annual incidence is only 0.6% with total prevalence of 2.1%, and progression is slow 1

Always investigate for structural heart disease in new-onset complete heart block, as the underlying cardiac pathology (not the block itself) often determines prognosis and mortality 1, 4

Recognize that HV interval prolongation accompanies advanced cardiac disease but death is typically due to the underlying heart disease rather than progression to complete block 1

In endocarditis, new-onset heart block is highly specific for perivalvular abscess and warrants urgent imaging and surgical evaluation 1

Post-MI complete heart block location matters: persistent advanced block in the His-Purkinje system (bilateral bundle branch block) requires permanent pacing, while AV nodal block may be transient 1