eMedicine Specialties > Cardiology > Arrhythmias

Third-Degree Atrioventricular Block: Differential Diagnoses & Workup

Author: Adam S Budzikowski, MD, PhD, Assistant Professor of Medicine, Division of Cardiovascular Medicine, Electrophysiology Section, State University of New York-Downstate, University Hospital of Brooklyn
Coauthor(s): Andrew C Corsello, MD, Consulting Staff, Department of Internal Medicine, Division of Cardiology, Cardiovascular Consultants of Maine, PA; James P Daubert, MD, Associate Professor of Medicine, Director of Electrophysiology Service, University of Rochester Medical Center; Consulting Staff, Atrial Fibrillation Clinic and Adult Congenital Heart Clinic, University of Rochester Medical Center, Strong Memorial Hospital; Abrar H Shah, MD, Consulting Staff, Department of Medicine-Cardiology, Strong Memorial Hospital, Geneva General Hospital; Consulting Staff, Department of Cardiology, Highland Hospital; Consulting Staff, Department of Cardiology and Electrophysiology, Park Ridge Hospital
Contributor Information and Disclosures

Updated: Jun 17, 2009

Differential Diagnoses

Junctional Rhythm
Second-Degree Atrioventricular Block

Other Problems to Be Considered

Ischemia should always be in the differential for a patient with new-onset, high-degree AV block. Take simple measures to rule out ischemia, such as 12-lead ECG and measurement of cardiac enzyme levels. If warranted, a more in-depth evaluation, including perfusion imaging, may be needed.

Iatrogenic heart block due to medications is not uncommon and should always be considered.

Workup

Laboratory Studies

  • Routine laboratory testing should include a measure of the serum potassium level, prothrombin time and activated partial thromboplastin time, and CBC count. If the patient is taking a drug (eg, digoxin) potentially responsible for the condition, the drug level should be measured.
  • The presence of fever or an elevated WBC count should be evaluated by using blood cultures because endocarditis can be complicated by heart block.
  • The decision to perform serologic test for Lyme disease or any of the collagen vascular diseases depends on other associated history and findings.

Imaging Studies

If examination findings or history suggest cardiomyopathy or valvular disease, then a transthoracic echocardiogram should be performed. Specific etiologies such as valve ring abscess may require transesophageal echo imaging. A determination of left ventricular function by echocardiogram or other technique can help in determining whether a pacemaker or defibrillator should be implanted for the treatment of the heart block.

Other Tests

  • If history or 12-lead ECG findings suggest active coronary artery disease, then cardiac enzyme levels measurements and an evaluation of ischemia, including either cardiac catheterization or stress testing, are needed.
  • The most important study is the 12-lead ECG.
    • Complete lack of conduction (no P waves cause a QRS complex) characterizes third-degree heart block.
    • If complete AV block exists, then the R-R interval is very regular; therefore, before diagnosing third-degree AV block, the R-R interval should be either marched out or measured.
    • If high-grade AV block exists without complete heart block, then some irregularity may occur during intervals following conducted P waves.
    • The various pathologies causing conduction system disease and heart block are listed in Causes. These systemic or myocardial diseases rarely present as conduction block, with the exception of Lyme disease, inferior myocardial infarction, and some of the neuromuscular diseases. Unless suggested by history, examination findings, family history, risk factors, or 12-lead ECG findings, the authors do not screen for underlying pathology.
    • Surface ECG and review of prior ECG data can provide important clues to the level of third-degree AV block. This can begin with a review of the current QRS width and morphology, comparing QRS during heart block to that when conducted (see Media file 1). If the QRS is narrow (<120 ms) during conducted beats and narrow with the same morphology during escape beats, then the block is in the AV junction. If the conducted QRS was narrow at baseline and is wide during the escape rhythm, then this is likely a distal level of block located anatomically in the His bundle or both the right and left bundles.

      ECG before and after complete heart block at the ...

      ECG before and after complete heart block at the AV nodal level.

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      ECG before and after complete heart block at the ...

      ECG before and after complete heart block at the AV nodal level.



      Complete heart block with wide complex escape.

      Complete heart block with wide complex escape.

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      Complete heart block with wide complex escape.

      Complete heart block with wide complex escape.

Procedures

  • Ambulatory monitoring may be performed to document heart-transient heart block or other bradyarrhythmias in patients presenting with symptoms suggestive of bradycardia.
  • Diagnostic electrophysiologic studies can be performed to assess AV conduction and to discern the level of block (AV nodal or infranodal) when necessary.

More on Third-Degree Atrioventricular Block

Overview: Third-Degree Atrioventricular Block
Differential Diagnoses & Workup: Third-Degree Atrioventricular Block
Treatment & Medication: Third-Degree Atrioventricular Block
Follow-up: Third-Degree Atrioventricular Block
Multimedia: Third-Degree Atrioventricular Block
References
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References

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  2. Finsterer J, Stöllberger C, Steger C, Cozzarini W. Complete heart block associated with noncompaction, nail-patella syndrome, and mitochondrial myopathy. J Electrocardiol. Oct 2007;40:352-4. [Medline]. [Full Text].

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  4. Abuin G, Nieponice A, Barcelo A, Rojas-Granados A, Leu PH, Arteaga-Martinez M. Anatomical reasons for the discrepancies in atrioventricular block after inferior myocardial infarction with and without right ventricular involvement. Tex Heart Inst J. 2009;36(1):8-11. [Medline].

  5. Nguyen HL, Lessard D, Spencer FA, Yarzebski J, Zevallos JC, Gore JM. Thirty-year trends (1975-2005) in the magnitude and hospital death rates associated with complete heart block in patients with acute myocardial infarction: a population-based perspective. Am Heart J. Aug 2008;156(2):227-33. [Medline].

  6. Merin O, Ilan M, Oren A, Fink D, Deeb M, Bitran D. Permanent pacemaker implantation following cardiac surgery: indications and long-term follow-up. Pacing Clin Electrophysiol. Jan 2009;32(1):7-12. [Medline].

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  17. Rardon DA, Miles WM, Mitrani RD, et al. Electrocardiographic Recognition: Atrioventricular Block and Dissociation. In: Zipes DP, Jalife J, eds. Cardiac Electrophysiology From Cell to Bedside. 2nd ed. Philadelphia, Pa: WB Saunders; 1995.

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Further Reading

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Keywords

third-degree atrioventricular block, third-degree AV block, AV block, heart block, complete AV block, complete heart block, first-degree AV block, 3rd degree heart block, third-degree heart block, cardiomyopathy, mitral calcification, aortic calcification, endocarditis, sudden cardiac death, SCD, Lenègre disease, Lev disease, rheumatic fever, myocarditis, Chagas disease, Lyme borreliosis, Aspergillus myocarditis, ankylosing spondylitis, Reiter syndrome, relapsing polychondritis, rheumatoid arthritis, scleroderma, amyloidosis, sarcoidosis, tumors, Hodgkin disease, multiple myeloma, Becker muscular dystrophy, myotonic muscular dystrophy, myocardial infarction, MI, hypoxia, hyperkalemia, AV dissociation, atrioventricular dissociation, pacemaker, implantable cardioverter-defibrillator, implantable cardioverter/defibrillator, ICD, neuromuscular disease, myotonic dystrophy, Duchenne muscular dystrophy, iatrogenic heart block

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Contributor Information and Disclosures

Author

Adam S Budzikowski, MD, PhD, Assistant Professor of Medicine, Division of Cardiovascular Medicine, Electrophysiology Section, State University of New York-Downstate, University Hospital of Brooklyn
Adam S Budzikowski, MD, PhD is a member of the following medical societies: American College of Cardiology, European Society of Cardiology, and Polish Society of Cardiology
Disclosure: Nothing to disclose.

Coauthor(s)

Andrew C Corsello, MD, Consulting Staff, Department of Internal Medicine, Division of Cardiology, Cardiovascular Consultants of Maine, PA
Disclosure: Nothing to disclose.

James P Daubert, MD, Associate Professor of Medicine, Director of Electrophysiology Service, University of Rochester Medical Center; Consulting Staff, Atrial Fibrillation Clinic and Adult Congenital Heart Clinic, University of Rochester Medical Center, Strong Memorial Hospital
James P Daubert, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Cardiology, American Heart Association, and Heart Rhythm Society
Disclosure: Medtronic Equity interest None; Boston Scientific Honoraria Speaking and teaching; CV Therapeutics Consulting fee Consulting; Cryocor Consulting fee Consulting

Abrar H Shah, MD, Consulting Staff, Department of Medicine-Cardiology, Strong Memorial Hospital, Geneva General Hospital; Consulting Staff, Department of Cardiology, Highland Hospital; Consulting Staff, Department of Cardiology and Electrophysiology, Park Ridge Hospital
Disclosure: Nothing to disclose.

Medical Editor

Robert E Fowles, MD, Clinical Professor of Medicine, University of Utah College of Medicine; Consulting Staff, Intermountain Medical Center and LDS Hospital; Director and Consulting Staff, Department of Cardiology, Salt Lake Clinic
Robert E Fowles, MD is a member of the following medical societies: American College of Cardiology, American College of Physicians, and American Heart Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

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; Reliant Grant/research funds Other; Novartis Honoraria Speaking and teaching; Novartis Consulting fee Consulting

CME Editor

Amer Suleman, MD, Consultant in Electrophysiology and Cardiovascular Medicine, Department of Internal Medicine, Division of Cardiology, Medical City Dallas Hospital
Amer Suleman, MD is a member of the following medical societies: American College of Physicians, American Heart Association, American Institute of Stress, American Society of Hypertension, Federation of American Societies for Experimental Biology, Royal Society of Medicine, and Society of Cardiac Angiography and Interventions
Disclosure: Nothing to disclose.

Chief Editor

Jeffrey N Rottman, MD, Professor of Medicine and Pharmacology, Director, Clinical Cardiac Electrophysiology Fellowship Program, 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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