Causes of Wenckebach (Mobitz Type I Second-Degree AV Block)
Wenckebach (Mobitz Type I second-degree AV block) is most commonly caused by increased vagal tone in healthy individuals, medication effects, and inferior wall myocardial infarction, with the block typically occurring at the level of the AV node. 1
Physiologic and Benign Causes
- Increased vagal tone is the most common cause in healthy individuals, particularly well-trained athletes and during sleep 2
- High-level athletic conditioning can lead to Wenckebach block as a physiologic adaptation 2, 3
- Sleep and obstructive sleep apnea can trigger vagotonic-associated Wenckebach block 2
Medication-Related Causes
- Beta-blockers (commonly prescribed for hypertension and heart failure) 2, 1
- Non-dihydropyridine calcium channel blockers (verapamil, diltiazem) 2, 1
- Digoxin (cardiac glycoside used for heart failure and atrial fibrillation) 2, 1
- Other antiarrhythmic drugs that slow AV conduction 2
Cardiac Pathology
- Inferior wall myocardial infarction (most common pathologic cause) 2, 4
- Acute coronary syndrome with or without significant coronary artery stenosis 5
- Myocarditis (inflammatory condition of the heart muscle) 2
- Valvular heart disease, particularly aortic valve stenosis 2
Structural and Congenital Heart Disease
- Congenital heart defects, especially repaired tetralogy of Fallot 1
- Congenitally corrected transposition of the great arteries 2, 1
- Cardiomyopathies (idiopathic, valvular, or ischemic) 2
Infectious and Inflammatory Causes
- Lyme carditis (cardiac manifestation of Lyme disease) 2, 1
- Bacterial endocarditis with perivalvar abscess 2
- Acute rheumatic fever 2
- Chagas disease (parasitic infection common in Latin America) 2
- Viral myocarditis 1
Infiltrative and Systemic Disorders
- Amyloidosis (protein deposition disease) 2
- Cardiac sarcoidosis (granulomatous inflammation) 2
- Rheumatologic diseases: systemic sclerosis, systemic lupus erythematosus, rheumatoid arthritis 2
Degenerative Causes
- Lev's and Lenegre's diseases (progressive fibrosis of the cardiac conduction system) 2
- Age-related degenerative changes of the conduction system 2
Metabolic and Endocrine Causes
- Acid-base disorders 2
- Thyroid disease (both hypothyroidism and hyperthyroidism) 2
- Adrenal disease (pheochromocytoma, hypoaldosteronism) 2
Iatrogenic Causes
- Catheter ablation procedures 2
- Cardiac surgery, especially valve surgery 2
- Transcatheter aortic valve replacement (TAVR) 2
- Alcohol septal ablation 2
Clinical Significance and Distinguishing Features
- Wenckebach block is characterized by progressive prolongation of the PR interval before a dropped QRS complex 2
- It typically occurs at the level of the AV node and is usually associated with a narrow QRS complex 2
- Unlike Mobitz Type II block, Wenckebach generally has a benign prognosis and rarely requires pacemaker implantation 2
- However, when Wenckebach block occurs during exercise (rather than resolving), it suggests disease in the His-Purkinje system and carries a worse prognosis 2, 6
- Wenckebach block with coexisting bundle branch block warrants electrophysiological study to identify potential intra-His or infra-His block that may require pacing 2
Important Distinction
- While Wenckebach block typically occurs at the AV node level, in rare cases it can occur in the infranodal conduction system, which predicts progression to complete heart block and necessitates cardiac pacing 6
- The anatomic site of the block (AV nodal vs. infranodal) is more clinically important than the ECG pattern classification 7