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Atrioventricular Block Workup

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

Laboratory Studies

Laboratory testing is not usually indicated in patients with atrioventricular (AV) block. Levels of electrolytes and drugs (eg, digitalis) can be checked in the case of second-degree or third-degree AV block when suspicion of increased potassium level or drug toxicity exists. In cases when second-degree and third-degree AV block might be a manifestation of acute myocardial infarction, cardiac enzymes should be measured.

If clinical evaluation suggests systemic illness, appropriate directed laboratory studies for infection, myxedema, or connective tissue disease should be performed.



Routine electrocardiographic (ECG) recording and cardiac monitoring with careful evaluation of the relationship between P waves and QRS complexes are the standard tests leading to proper diagnosis of AV blocks.

Identifying episodes of transient AV block with sudden pauses and/or low heart rate causing syncopal episodes may require 24-hour Holter monitoring, multiple ECG recordings, event (loop) ECG recordings, or, in selected cases, monitoring with implantable loop recorders (Reveal, Medtronic, Inc; Confirm, St Jude Medical, Inc).


Electrophysiologic Testing

Electrophysiologic testing is indicated in a patient with suspected AV block as the cause of syncope. The invasive recording of AH (atrium-His) and HV (His-ventricle) intervals may determine the degree of conduction abnormality and may guide decision making for pacemaker therapy. As noted, in selected cases, invasive diagnostic procedures may include implantation of a loop recorder.


Imaging Studies

In general, routine imaging studies are not helpful in diagnosing AV blocks.

However, imaging studies (eg, echocardiography) might be useful in diagnosing underlying comorbid conditions, such as aortic valve stenosis with calcification, wall motion abnormalities in acute ischemia, cardiomyopathy, and congenital heart disease (eg, congenitally corrected transposition of the great vessels).



Advanced heart block, such as Mobitz II or third-degree AV block, may become more symptomatic with increased activity, where an actual increase in block and decrease in effective heart rate may occur.

Exercise may be used to evaluate 2:1 heart block and differentiate Mobitz I second-degree AV block (where the conducted rate increases) from Mobitz II AV block (where the block becomes more significant and often symptomatic).

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.

  1. [Guideline] Epstein AE, Dimarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: executive summary. Heart Rhythm. 2008 Jun. 5(6):934-55. [Medline].

  2. [Guideline] Epstein AE, DiMarco JP, Ellenbogen KA, Estes NA 3rd, Freedman RA, Gettes LS, et al. 2012 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2013 Jan 22. 61(3):e6-75. [Medline].

  3. Schott JJ, Alshinawi C, Kyndt F, et al. Cardiac conduction defects associate with mutations in SCN5A. Nat Genet. 1999 Sep. 23(1):20-1. [Medline].

  4. Nery PB, Beanlands RS, Nair GM, Green M, Yang J, McArdle BA, et al. Atrioventricular block as the initial manifestation of cardiac sarcoidosis in middle-aged adults. J Cardiovasc Electrophysiol. 2014 Aug. 25(8):875-81. [Medline].

  5. Saleh F, Greene EA, Mathison D. Evaluation and management of atrioventricular block in children. Curr Opin Pediatr. 2014 Jun. 26(3):279-85. [Medline].

  6. Cheng S, Keyes MJ, Larson MG, et al. Long-term outcomes in individuals with prolonged PR interval or first-degree atrioventricular block. JAMA. 2009 Jun 24. 301(24):2571-7. [Medline]. [Full Text].

  7. Crisel RK, Farzaneh-Far R, Na B, Whooley MA. First-degree atrioventricular block is associated with heart failure and death in persons with stable coronary artery disease: data from the Heart and Soul Study. Eur Heart J. 2011 Aug. 32(15):1875-80. [Medline].

  8. Kuleva M, Le Bidois J, Decaudin A, et al. Clinical course and outcome of antenatally detected atrioventricular block: experience of a single tertiary centre and review of the literature. Prenat Diagn. 2014 Dec 8. [Medline].

  9. Stiles S. BLOCK-HF: replace RV pacing with BiV in AV-block heart failure. Heartwire. Nov 8, 2012. [Full Text].

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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