First Degree Atrioventricular Block

First degree blocks are characterized by a prolonged PR interval (greater than 200 ms) and are usually seen it active, healthy patients without heart disease. It usually represents high vagal tone within the atrioventricular node itself and is unlikely to progress to complete heart block; however, when accompanied by preexisting conduction disease (e.g. right bundle branch block, left bundle branch block, or bifascicular block) it can indicate infranodal conduction disease.



  1. Surawicz B, Childers R, Deal BJ, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol. 2009;53(11):976-81.
  2. Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines, and the Heart Rhythm Society. J Am Coll Cardiol. 2019;74(7):932-987.