eMedicine Specialties > Emergency Medicine > Cardiovascular

Heart Block, Third Degree: Differential Diagnoses & Workup

Author: Michael D Levine, MD, Physician, Department of Medical Toxicology, Banner Good Samaritan Medical Center
Coauthor(s): David FM Brown, MD, Assistant Professor, Department of Medicine, Division of Emergency Medicine, Harvard Medical School; Associate-Chief, Attending Physician, Department of Emergency Medicine, Massachusetts General Hospital
Contributor Information and Disclosures

Updated: Apr 13, 2009

Differential Diagnoses

Heart Block, Second Degree
Myocardial Infarction
Myocarditis
Sinus Bradycardia

Other Problems to Be Considered

Bradycardia with a ventricular escape
Bradycardia with a junctional escape
Accelerated junctional escape rhythm

Workup

Laboratory Studies

  • Serum electrolytes levels, including potassium and magnesium, to look for metabolic imbalance, indications of renal insufficiency or failure, and particularly for severe hyperkalemia.
  • A digoxin level should be obtained for patients on digoxin or in whom ingestion of digoxinlike compounds (eg, Lily of the Valley, Oleander, Foxglove, Bufonidae toads) is suspected.
  • Lyme titers should be obtained from patients who may have been exposed to Lyme disease. Remember that cardiac manifestations of Lyme disease are delayed, so Lyme-induced heart block can occur during any season.
  • Myocarditis-related laboratory studies should be performed in patients suspected of having myocarditis. Such studies include Lyme titers, HIV serologies, enterovirus polymerase chain reaction (PCR), adenovirus PCR, and Chagas titers, as clinically appropriate.
  • For most patients with illness serious enough to cause third-degree AV block, a complete blood count is indicated to screen for coincident problems (eg, anemia, infection) that may require ED intervention.

Imaging Studies

  • A chest radiograph should be obtained.
  • If myocarditis or a pericardial effusion is a concern, an echocardiogram should be performed.

Other Tests

  • Cardiac enzymes are indicated for any patient with suspected myocardial ischemia.
  • All patients must have at least one 12-lead electrocardiogram. Ideally, serial electrocardiograms should be performed.

Procedures

  • Cardiac pacing may be initially indicated or may be indicated if a patient deteriorates. Because the situation may be urgent, all patients should have transcutaneous pacing pads applied.
    • For patients who are symptomatic (dyspnea, chest pain, myocardial ischemia or MI, CHF, altered mental status), the transcutaneous pacer should be activated immediately. If the external pacer fails to capture, a transvenous pacer should be inserted emergently.
    • For patients who are asymptomatic, the transcutaneous pacer should be tested. If the external pacer fails to capture, urgent placement of a transvenous pacer should be considered. Indications for placement would include bradycardia that is ineligible or unresponsive to treatment with medications.

More on Heart Block, Third Degree

Overview: Heart Block, Third Degree
Differential Diagnoses & Workup: Heart Block, Third Degree
Treatment & Medication: Heart Block, Third Degree
Follow-up: Heart Block, Third Degree
Multimedia: Heart Block, Third Degree
References
Further Reading
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References

  1. Narula OS, Scherlag BJ, Javier RP, Hildner FJ, Samet P. Analysis of the A-V conduction defect in complete heart block utilizing His bundle electrograms. Circulation. Mar 1970;41(3):437-48. [Medline].

  2. Rosen KM, Dhingra RC, Loeb HS, Rahimtoola SH. Chronic heart block in adults. Clinical and electrophysiological observations. Arch Intern Med. May 1973;131(5):663-72. [Medline].

  3. Costedoat-Chalumeau N, Georgin-Lavialle S, Amoura Z, Piette JC. Anti-SSA/Ro and anti-SSB/La antibody-mediated congenital heart block. Lupus. 2005;14(9):660-4. [Medline].

  4. Bestetti RB, Cury PM, Theodoropoulos TA, Villafanha D. Trypanosoma cruzi myocardial infection reactivation presenting as complete atrioventricular block in a Chagas' heart transplant recipient. Cardiovasc Pathol. Nov-Dec 2004;13(6):323-6. [Medline].

  5. Epstein AE, DiMarco JP, Ellenbogen KA, Estes NA 3rd, Freedman RA, Gettes LS, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices) developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. J Am Coll Cardiol. May 27 2008;51(21):e1-62. [Medline].

  6. American Heart Association. Guidelines for cardiopulmonary resuscitation and emergency cardiac care. Emergency Cardiac Care Committee and Subcommittees, American Heart Association. Part III. Adult advanced cardiac life support. JAMA. Oct 28 1992;268(16):2199-241. [Medline].

  7. International Laison Committee on Resuscitation. 2005 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations. Part 4: Advanced life support. Resuscitation. Nov-Dec 2005;67(2-3):213-47. [Medline].

  8. Syverud S. Cardiac pacing. Emerg Med Clin North Am. May 1988;6(2):197-215. [Medline].

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Further Reading

Clinical guidelines

Adult basic life support: 2005 International Consensus Conference on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations.Adult basic life support. In: 2005 International Consensus Conference on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations. Circulation 2005 Nov 29;112(22 Suppl):III5-16.

Advanced life support: 2005 International Consensus Conference on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations. Advanced life support. In: 2005 International Consensus Conference on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations. Circulation 2005 Nov 29;112(22 Suppl):III25-54.

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Keywords

heart block, third-degree heart block, atrioventricular block, AV block, third-degree atrioventricular block, third-degree AV block, complete heart block, AV node, cardiac conduction system, AV dissociation, atrioventricular dissociation, His bundle

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Contributor Information and Disclosures

Author

Michael D Levine, MD, Physician, Department of Medical Toxicology, Banner Good Samaritan 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.

Coauthor(s)

David FM Brown, MD, Assistant Professor, Department of Medicine, Division of Emergency Medicine, Harvard Medical School; Associate-Chief, Attending Physician, 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: Schering  Honoraria Speaking and teaching

Medical Editor

Theodore J Gaeta, DO, MPH, FACEP, Clinical Associate Professor, Department of Emergency Medicine, Joan and Sanford Weill Medical College at Cornell University; 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.

Pharmacy Editor

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

Managing Editor

Eddy Lang, MDCM, CCFP (EM), CSPQ, Assistant Professor, Department of Family Medicine, McGill University; Consulting Staff, Department of Emergency Medicine, The Sir Mortimer B Davis-Jewish General Hospital
Eddy Lang, MDCM, CCFP (EM), CSPQ is a member of the following medical societies: American College of Emergency Physicians
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

David FM Brown, MD, Assistant Professor, Department of Medicine, Division of Emergency Medicine, Harvard Medical School; Associate-Chief, Attending Physician, 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: Schering  Honoraria Speaking and teaching

 
 
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