What is the management of a first-degree atrioventricular (AV) block found on an electrocardiogram (ECG)?

Management of First-Degree Atrioventricular Block

First-degree atrioventricular (AV) block is generally benign and asymptomatic, requiring only monitoring without specific treatment in most cases. 1

Definition and Characteristics

• First-degree AV block is defined as a prolonged PR interval >200 ms on ECG, representing delayed conduction through the AV node, but with all atrial impulses still conducting to the ventricles 2
• It is technically a misnomer as there is only delay and no actual block in the AV conduction system 3
• First-degree AV block typically occurs at the level of the AV node and is generally benign 2

Evaluation Approach

• For asymptomatic patients with first-degree AV block and PR interval <300 ms:

  • No further testing is typically required if the QRS duration is normal 1
  • Regular follow-up with routine ECG monitoring is sufficient 1

• For patients with PR interval ≥300 ms or abnormal QRS:

  • Consider echocardiogram to rule out structural heart disease 1
  • Exercise stress test to assess PR interval shortening during exercise 1
  • 24-hour ambulatory monitoring to detect potential progression to higher-degree block 1, 4

Management Based on Symptoms

Asymptomatic Patients

• No specific treatment is required for asymptomatic first-degree AV block 1
• Permanent pacemaker implantation is not indicated for asymptomatic first-degree AV block 1
• Athletes with asymptomatic first-degree AV block can participate in all competitive sports unless otherwise excluded by underlying structural heart disease 1

Symptomatic Patients

• For patients with symptoms similar to pacemaker syndrome (fatigue, exertional intolerance) due to profound first-degree AV block:

  • Consider permanent pacing if symptoms are clearly attributable to the AV block 1
  • Symptoms may occur when PR interval is markedly prolonged, causing loss of AV synchrony 1, 5

• For patients with exertional symptoms:

  • Exercise treadmill testing is reasonable to determine whether they may benefit from permanent pacing 1

Special Considerations

• Monitor for progression to higher-degree AV block, especially in patients with:

  • Bifascicular block in addition to first-degree AV block 1
  • Neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome) 1, 2
  • PR interval >300 ms 3, 4

• Recent evidence suggests first-degree AV block may not be entirely benign in all patients:

  • It can be a marker for more severe intermittent conduction disease 4
  • Long-term monitoring with insertable cardiac monitors has shown progression to higher-grade block in some patients 4

When to Consider Referral to Cardiology

• First-degree AV block with:
  • Symptoms of fatigue or exercise intolerance 1
  • PR interval >300 ms 1, 3
  • Coexisting bundle branch block or bifascicular block 1
  • Structural heart disease 1
  • Evidence of progression to higher-degree block on monitoring 4

Prognosis

• Most cases of isolated first-degree AV block have excellent prognosis 2
• Patients should be educated about symptoms that might indicate progression to higher-degree block (syncope, pre-syncope, severe fatigue) 4
• Regular follow-up with ECG is recommended, especially in those with PR interval >300 ms or coexisting conduction abnormalities 1, 4