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Atrioventricular Block Differential Diagnoses

  • Author: Chirag M Sandesara, MD; Chief Editor: Jeffrey N Rottman, MD  more...
Updated: Dec 18, 2014

Diagnostic Considerations

In making the diagnosis, it is important to differentiate Mobitz I second-degree atrioventricular (AV) block from Mobitz II second-degree AV block, as well as to differentiate Mobitz II second-degree AV block from third-degree AV block. Both Mobitz I and Mobitz II AV block must be differentiated from sinus nodal dysfunction.

Atrial fibrillation with a low heart rate may mask third-degree AV block. Third-degree block must be differentiated from AV dissociation, where the frequency of the ventricular rhythm exceeds the frequency of the atrial rhythm.

Differential Diagnoses

Contributor Information and Disclosures

Chirag M Sandesara, MD Virginia Cardiovascular Associates, Cardiac Rhythm Care

Chirag M Sandesara, MD is a member of the following medical societies: American College of Cardiology, American College of Physicians-American Society of Internal Medicine, American Heart Association, American Medical Association, Heart Rhythm Society

Disclosure: Nothing to disclose.


Brian Olshansky, MD Professor Emeritus of Medicine, Department of Internal Medicine, University of Iowa College of Medicine

Brian Olshansky, MD is a member of the following medical societies: American College of Cardiology, American Heart Association, Cardiac Electrophysiology Society, Heart Rhythm Society

Disclosure: Speaker, consultant, DSMB for: Lundbeck; Daiichi Sankyo, Amarin, On-X, Biotronik.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Steven J Compton, MD, FACC, FACP, FHRS Director of Cardiac Electrophysiology, Alaska Heart Institute, Providence and Alaska Regional Hospitals

Steven J Compton, MD, FACC, FACP, FHRS is a member of the following medical societies: American College of Physicians, American Heart Association, American Medical Association, Heart Rhythm Society, Alaska State Medical Association, American College of Cardiology

Disclosure: Nothing to disclose.

Chief Editor

Jeffrey N Rottman, MD Professor of Medicine, Department of Medicine, Division of Cardiovascular Medicine, University of Maryland School of Medicine; Cardiologist/Electrophysiologist, University of Maryland Medical System and VA Maryland Health Care System

Jeffrey N Rottman, MD is a member of the following medical societies: American Heart Association, Heart Rhythm Society

Disclosure: Nothing to disclose.


The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous authors Wojciech Zareba, MD, PhD, FACC, and Stacy D Fisher, MD, to the development and writing of the source article.

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First-degree atrioventricular block. PR interval is constant and is 280 msec.
Second-degree atrioventricular block, Mobitz type I (Wenckebach). Note the prolongation of the PR interval preceding the dropped beat and the shortened PR interval following the dropped beat.
Second-degree atrioventricular block, Mobitz type II. A constant PR interval in conducted beats is present. Intraventricular conduction delay also is present.
Third-degree atrioventricular block (complete heart block). The atrial rate is faster than the ventricular rate, and no association exists between the atrial and ventricular activity.
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