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Pediatric Second-Degree Atrioventricular Block Differential Diagnoses

  • Author: M Silvana Horenstein, MD; Chief Editor: P Syamasundar Rao, MD  more...
Updated: Mar 02, 2016

Diagnostic Considerations

The differential diagnosis of second-degree atrioventricular (AV) block is limited, although the potential etiologies may widely vary. Atrial tachycardias with second-degree block or nonconducted premature atrial stimuli are occasionally mistaken for second-degree AV block. This may be avoided by paying close attention to the P-wave rate, morphology, and regularity, recognizing that some sinus arrhythmia is a normal finding in children. Marked sinus arrhythmia is also often mistaken for second-degree AV block.

Differentiating ECG AV block into its subtypes of Wenckebach, non-Wenckebach, 2:1, or high-grade AV is very important.

Differential Diagnoses

Contributor Information and Disclosures

M Silvana Horenstein, MD Assistant Professor, Department of Pediatrics, University of Texas Medical School at Houston; Medical Doctor Consultant, Legacy Department, Best Doctors, Inc

M Silvana Horenstein, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Medical Association

Disclosure: Nothing to disclose.


Robert Murray Hamilton, MD, MSc, FRCPC Electrophysiologist, Senior Associate Scientist, Physiology and Experimental Medicine, Labatt Family Heart Centre; Professor, Department of Pediatrics, University of Toronto Faculty of Medicine

Robert Murray Hamilton, MD, MSc, FRCPC is a member of the following medical societies: American Heart Association, Canadian Medical Association, Ontario Medical Association, Royal College of Physicians and Surgeons of Canada, Canadian Medical Protective Association, Heart Rhythm Society, Canadian Cardiovascular Society, Cardiac Electrophysiology Society, Pediatric and Congenital Electrophysiology Society, Society for Pediatric Research

Disclosure: Nothing to disclose.

Chief Editor

P Syamasundar Rao, MD Professor of Pediatrics and Medicine, Division of Cardiology, Emeritus Chief of Pediatric Cardiology, University of Texas Medical School at Houston and Children's Memorial Hermann Hospital

P Syamasundar Rao, MD is a member of the following medical societies: American Academy of Pediatrics, American Pediatric Society, American College of Cardiology, American Heart Association, Society for Cardiovascular Angiography and Interventions, Society for Pediatric Research

Disclosure: Nothing to disclose.


Charles I Berul, MD Professor of Pediatrics and Integrative Systems Biology, George Washington University School of Medicine; Chief, Division of Cardiology, Children's National Medical Center

Charles I Berul, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Cardiology, American Heart Association, Cardiac Electrophysiology Society, Heart Rhythm Society, Pediatric and Congenital Electrophysiology Society, and Society for Pediatric Research

Disclosure: Johnson & Johnson Consulting fee Consulting

Alvin J Chin, MD Professor of Pediatrics, University of Pennsylvania School of Medicine; Attending Physician, Cardiology Division, Children's Hospital of Philadelphia

Alvin J Chin, MD, is a member of the following medical societies: American Association for the Advancement of Science, American Heart Association, and Society for Developmental Biology

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

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A common pattern of second-degree atrioventricular (AV) block consists of gradual prolongation of the PR interval leading up to a nonconducted P wave; this pattern is known as Wenckebach AV block, or Mobitz I AV block. This rhythm strip is an example of classic Mobitz I, or Wenckebach, AV block, in which the PR interval prolongs by sequentially smaller increments, with consequent shortening of the RR intervals until the blocked beat occurs. However, classic Wenckebach block is present in only a minority of cases. Wenckebach block is most easily diagnosed by comparing the PR interval following the blocked beat with the PR interval preceding the blocked beat; if the PR interval shortens following the blocked beat, the block is most likely of the Wenckebach type.
If there is no progressive prolongation of the PR interval and the PR interval fails to shorten following a blocked beat, non-Wenckebach AV block (or Mobitz II AV block) is said to be present. This block is usually located more distally in the His bundle or the His bundle branches, or both, and the escape rates are usually slower and less stable.
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