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Atrioventricular Block Clinical Presentation

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


First-degree atrioventricular (AV) block is generally not associated with any symptoms and is usually an incidental finding on electrocardiography (ECG). People with newly diagnosed first-degree AV block may be healthy individuals with high vagal tone (eg, well-conditioned athletes), or they may have a history of myocardial infarction or myocarditis. First-degree AV block also may represent the first sign of a degenerative process of the AV conduction system.

Second-degree AV block usually is asymptomatic. However, in some patients, sensed irregularities of the heartbeat, presyncope, or syncope may occur. The latter usually is observed in more advanced conduction disturbances, such as Mobitz II second-degree AV block. A history of medications that affect atrioventricular node (AVN) function (eg, digitalis, beta-blockers, and calcium channel blockers) may be contributory and should be obtained.

Third-degree AV block frequently is associated with symptoms such as fatigue, dizziness, light-headedness, presyncope, and syncope most commonly. Syncopal episodes due to slow heart rates are called Morgagni-Adams-Stokes (MAS) episodes, in recognition of the pioneering work of these researchers on syncope. Patients with third-degree AV block may have associated symptoms of acute myocardial infarction either causing the block or related to reduced cardiac output from bradycardia in the setting of advanced atherosclerotic coronary artery disease.

Any level of atrioventricular block leading to profound bradycardia may also lead to life-threatening torsades de pointes.


Physical Examination

Routine physical examination does not lead to the diagnosis of first-degree AV block. Second-degree AV block may manifest on physical examination as bradycardia (especially Mobitz II), irregularity of heart rate (especially Mobitz I [Wenckebach]), or both.

Third-degree AV block is associated with profound bradycardia unless the site of the block is located in the proximal portion of the AVN. Exacerbation of ischemic heart disease or congestive heart failure caused by AV block–related bradycardia and reduced cardiac output may lead to specific clinically recognizable symptoms (eg, chest pain, dyspnea, confusion, and pulmonary edema). Cannon a waves may be observed intermittently in the jugular venous pulsation when the right atrium contracts against a closed tricuspid valve due to atrioventricular dissociation.



Complications include the following:

  • Sudden death due to asystole or secondary to polymorphic ventricular tachyarrhythmias
  • Cardiovascular collapse with syncope, aggravation of ischemic heart disease, congestive heart failure, and exacerbation of renal disease
  • Head and musculoskeletal injuries during syncopal episodes
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, Heart Rhythm Society, Cardiac Electrophysiology Society, American Heart Association

Disclosure: Received honoraria from Guidant/Boston Scientific for speaking and teaching; Received honoraria from Medtronic for speaking and teaching; Received consulting fee from Guidant/Boston Scientific for consulting; Received consulting fee from BioControl for consulting; Received consulting fee from Boehringer Ingelheim for consulting; Received consulting fee from Amarin for review panel membership; Received consulting fee from sanofi aventis for review panel membership.

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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