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First-degree atrioventricular block
Other Resources UpToDate PubMed

First-degree atrioventricular block

Contributors: Young Ju Esther Lee MD, Ryan Hoefen MD, PhD
Other Resources UpToDate PubMed


First-degree atrioventricular (AV) block refers to delayed electrical conduction between the atrium and the ventricle. It is identified by a long PR interval (> 200 msec). In adults, the conduction delay most commonly occurs within the AV node.

Potential underlying causes for first-degree AV block include myocardial infarction, coronary artery disease, neuromuscular disorders, and infiltrative disorders such as sarcoidosis, systemic lupus erythematosus, bacterial endocarditis, and Lyme carditis. Medications that block the AV node such as beta blockers, non-dihydropyridine calcium channel blockers, and digoxin may also cause first-degree AV block.

First-degree AV block is associated with increased vagal tone in younger patients (which reduces the rate of impulse conduction) and age-related conduction abnormalities in the elderly. Most patients are asymptomatic, but rarely patients may present with dyspnea, lightheadedness, presyncope, syncope, fatigue, or exercise intolerance, particularly if the patient has intermittently occurring second-degree or third-degree AV block.


I44.0 – Atrioventricular Block, First-Degree

270492004 – First degree atrioventricular block

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Hyperthyroidism
  • Complete atrioventricular block
  • Second-degree atrioventricular block
  • Ectopic atrial rhythm
  • Atrial flutter
  • Atrial fibrillation with slow ventricular response
  • Atrial escape rhythm
  • Sinus bradycardia
  • Sinus node dysfunction
  • Acute Acute coronary syndrome
  • Hyperkalemia
  • Lyme carditis (see Lyme disease)
  • American trypanosomiasis
  • Sympatholytic syndrome, Sympatholytic syndrome, or Digitalis toxicity

Best Tests

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Management Pearls

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Drug Reaction Data

Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.

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Last Reviewed:04/09/2020
Last Updated:04/09/2020
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First-degree atrioventricular block
A medical illustration showing key findings of First-degree atrioventricular block : Fatigue, Syncope, Dyspnea
Copyright © 2024 VisualDx®. All rights reserved.