Intrinsic conduction/ structural defects particularly those located in this intra His Bundle (intrinsic paroxysmal AV block), low adenosine levels (idiopathic paroxysmal AV block) and increase vagal tone/vagal surge (extrinsic vagal paroxysmal AV block) are the major causes of paroxysmal AV block. However, several reversible causes need to be ruled out before coming to a diagnosis.

• Intrinsic conduction/ structural defects particularly those located in this intra His Bundle (intrinsic paroxysmal AV block), low adenosine levels (idiopathic paroxysmal AV block) and increase vagal tone/vagal surge (extrinsic paroxysmal AV block) are the major causes of paroxysmal AV block.
• However, some studies have shown an association of AV nodal blocking agents (beta blockers, calcium channel blockers), degenerative valvular heart disease, degeneration of the conduction system (the His bundle in particular), acute coronary syndromes (inferior /anterior wall myocardial infarction in particular) and paroxysmal AV block.
• Less common causes that have been cited are Lev- Lenegre disease, aneurysmal membranous septum, rheumatic heart disease, mitral valvulitis, sarcoidosis, h/o surgery and infective endocarditis with abscess formation.^[1]
• A study of 20 patients conducted by Zabarski et al found that ischemic heart disease, dilated cardiomyopathy, carotid sinus hypersensitivity, chronic AV blocker consumption and aortic valve replacement were associated paroxysmal AV block.^[2]