First-Degree Atrioventricular Block Workup

Author: Jamshid Alaeddini, MD, FACC; Chief Editor: Jeffrey N Rottman, MD more...

Updated: Jun 29, 2011

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Approach Considerations
Electrocardiography
Ultrasonography
Histologic Findings
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Approach Considerations

First-degree atrioventricular (AV) block is frequently noted as an incidental finding on electrocardiography (ECG).

Routine laboratory studies are usually not indicated in the evaluation of first-degree AV block. Electrolyte and drug screen can be obtained if a metabolic derangement or drug toxicity is suspected. Routine imaging studies are not indicated for first-degree AV block.

Electrocardiography

On a surface ECG, the PR interval exceeds 200 msec, and all P waves conduct to the ventricle with constant but prolonged PR interval (see the images below).

The PR interval is 0.24 seconds (240 ms) in this patient with asymptomatic first-degree atrioventricular block.

ECG in a patient with first-degree heart block.

ECG in patient with first-degree heart block.

His bundle ECG is necessary only in patients with symptomatic (ie, presyncope and syncope) first-degree AV block and a wide QRS complex, indicative of bundle-branch block. The study is used to locate the site of the block in these patients. As many as 50% of patients show an infranodal conduction delay.

Follow-up ECGs may be indicated in patients who are treated with AV nodal agents while in the emergency department (ED), as well as for patients with a concomitant myocardial infarction (MI).

Ultrasonography

In patients with first-degree AV block and left ventricular systolic dysfunction, Doppler ultrasonography may be used to document an improvement in cardiac output during dual-chamber pacing at short AV delay. This may provide evidence for the appropriateness of implanting a permanent pacemaker for hemodynamic support in such patients.

More recently, cardiac resynchronization therapy (ie, biventricular pacing) has been applied in patients with cardiomyopathy, congestive heart failure, or intraventricular conduction delay (IVCD). First-degree AV block is frequently present in these patients as well.

Histologic Findings

Under light microscopy, an atrioventricular node (AVN) is seen to be composed of a thick mesh of tiny pale cells, which anastomose with one another via short pluridirectional cytoplasmic projections. Under electron microscopy, 4 types of cells are observed in the AVN: transitional cells, P cells, common myocardial cells, and Purkinje cells.

Three functional regions have been described in the AVN on the basis of their differing conductive properties: atrionodal (AV), nodal (N), and nodal-His (NH). Cells in the N region have slower conduction times than the other regions and have no automaticity properties. Cells of the AN and NH regions have faster conduction times and display spontaneous diastolic repolarization activity.

Proceed to Treatment & Management

Contributor Information and Disclosures

Author

Jamshid Alaeddini, MD, FACC Clinical Cardiac Electrophysiologist, Inland Cardiology Associates

Jamshid Alaeddini, MD, FACC is a member of the following medical societies: American College of Cardiology and American Heart Association

Disclosure: Boston Scientific Honoraria Speaking and teaching; Medtronic Honoraria Speaking and teaching; St. Jude Honoraria Speaking and teaching; Reliant Honoraria Speaking and teaching

Coauthor(s)

Theodore J Gaeta, DO, MPH, FACEP Clinical Associate Professor, Department of Emergency Medicine, Weill Cornell Medical College; Vice Chairman and Program Director of Emergency Medicine Residency Program, Department of Emergency Medicine, New York Methodist Hospital; Academic Chair, Adjunct Professor, Department of Emergency Medicine, St George's University School of Medicine

Theodore J Gaeta, DO, MPH, FACEP is a member of the following medical societies: Alliance for Clinical Education, American College of Emergency Physicians, Clerkship Directors in Emergency Medicine, Council of Emergency Medicine Residency Directors, New York Academy of Medicine, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Michael D Levine, MD Physician, Department of Medical Toxicology, Banner Good Samaritan Medical Center; Physician, Department of Emergency Medicine, Banner Thunderbird Medical Center

Michael D Levine, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Emergency Physicians, American College of Medical Toxicology, American Medical Association, Emergency Medicine Residents Association, Phi Beta Kappa, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Jamshid Shirani, MD Director of Cardiology Fellowship Program, Director of Echocardiography Laboratory, St Luke's Hospital and Health Network

Jamshid Shirani, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Cardiology, American College of Physicians, American Federation for Medical Research, American Heart Association, American Society of Echocardiography, and Association of Subspecialty Professors

Disclosure: Nothing to disclose.

Specialty Editor Board

Eddy S Lang, MDCM, CCFP(EM), CSPQ Associate Professor, Senior Researcher, Division of Emergency Medicine, Department of Family Medicine, University of Calgary Faculty of Medicine; Assistant Professor, Department of Family Medicine, McGill University Faculty of Medicine, Canada

Eddy S Lang, MDCM, CCFP(EM), CSPQ is a member of the following medical societies: American College of Emergency Physicians, Canadian Association of Emergency Physicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

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

Disclosure: Medscape Salary Employment

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

Brian Olshansky, MD is a member of the following medical societies: American Autonomic Society, American College of Cardiology, American College of Chest Physicians, American College of Physicians, American College of Sports Medicine, American Federation for Clinical Research, American Heart Association, Cardiac Electrophysiology Society, Heart Rhythm Society, and New York Academy of Sciences

Disclosure: Guidant/Boston Scientific Honoraria Speaking and teaching; Medtronic Honoraria Speaking and teaching; Guidant/Boston Scientific Consulting fee Consulting; Novartis Honoraria Speaking and teaching; Novartis Consulting fee Consulting

David FM Brown, MD Associate Professor, Division of Emergency Medicine, Harvard Medical School; Vice Chair, Department of Emergency Medicine, Massachusetts General Hospital

David FM Brown, MD is a member of the following medical societies: American College of Emergency Physicians and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

Jeffrey N Rottman, MD Professor of Medicine and Pharmacology, Vanderbilt University School of Medicine; Chief, Department of Cardiology, Nashville Veterans Affairs Medical Center

Jeffrey N Rottman, MD is a member of the following medical societies: American Heart Association and North American Society of Pacing and Electrophysiology (NASPE)

Disclosure: Nothing to disclose.

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The PR interval is 0.24 seconds (240 ms) in this patient with asymptomatic first-degree atrioventricular block.

ECG in a patient with first-degree heart block.

ECG in patient with first-degree heart block.

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