Causes and Clinical Significance of Second Degree Heart Block
Pathophysiology and Location
- Second-degree heart block is primarily caused by conduction system disease, ischemic heart disease, medications, and structural heart abnormalities, with the specific etiology varying by block type (Mobitz I vs II) 1
- Mobitz Type I (Wenckebach) second-degree AV block typically occurs at the level of the AV node 2
- Mobitz Type II second-degree AV block occurs within or below the His bundle in the His-Purkinje system 1
Common Causes
- Increased vagal tone is the most common cause of Mobitz Type I second-degree AV block in healthy individuals 2
- Medications such as beta-blockers, non-dihydropyridine calcium channel blockers, and digoxin can cause Mobitz Type I second-degree AV block 3
- Ischemic heart disease, particularly anterior wall myocardial infarction, is a common cause of Mobitz Type II second-degree AV block 1
- Degenerative conduction system disease, such as Lev's and Lenegre's diseases, can cause Mobitz Type II second-degree AV block 1
Clinical Significance
- Mobitz Type II block is generally considered more serious than Mobitz Type I due to higher risk of progression to complete heart block 1
- Second-degree block occurring during exercise suggests disease in the His-Purkinje system and is associated with poor prognosis, according to the American College of Cardiology 5
Congenital Heart Disease
- Repaired tetralogy of Fallot is commonly associated with second-degree AV block, as reported by the European Heart Journal 4
- Congenitally corrected transposition of the great arteries can present with AV block 3