Atrioventricular (AV) blocks either delay or completely block impulses from the atria into the ventricles. 

Causes of AV Block 

• Increased vagal tone during sleep, athletic training, or stimulation of the carotid sinus 
• Damage to the conduction system secondary to hereditary fibrosis or sclerosis (idiopathic progressive cardiac conduction disease)
• Ischemic heart disease—causes 40% of AV blocks 
• Cardiomyopathy, myocarditis, congenital heart disease, and familial disease 
• Serum potassium concentration > 6.3 mEq/L
• Medications such as verapamil, diltiazem, amiodarone, adenosine 
• Cardiac surgeries and catheter ablations performed to treat arrhythmias