What is the management plan for first degree atrioventricular block (AVB)?

Management of First-Degree Atrioventricular Block

For most patients with first-degree AV block, no treatment is required—observation with routine ECG monitoring is sufficient unless the PR interval exceeds 300 ms or symptoms clearly attributable to the conduction delay are present. 1

Understanding First-Degree AV Block

First-degree AV block is actually a misnomer—it represents delayed conduction (PR interval >200 ms) rather than true block, since all atrial impulses still conduct to the ventricles. 2 For this reason, it is more accurately termed "first-degree AV delay." 2

Initial Evaluation Strategy

For Asymptomatic Patients with PR <300 ms:

• No further testing is typically required if QRS duration is normal. 1
• Regular follow-up with routine ECG monitoring is sufficient. 1
• Athletes with asymptomatic first-degree AV block can participate in all competitive sports unless structural heart disease is present. 1

For Patients Requiring Further Workup:

Pursue additional evaluation if any of the following are present:

• PR interval ≥300 ms 1
• Abnormal QRS duration or bundle branch block 1
• Symptoms of fatigue, exercise intolerance, or lightheadedness 2, 1
• Coexisting bifascicular block 1
• Neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome) 1

Recommended testing includes:

• Transthoracic echocardiogram to exclude structural heart disease 1
• Exercise stress test to assess whether PR interval shortens appropriately with exercise 1
• 24-hour ambulatory ECG monitoring to detect progression to higher-degree block 1

When Permanent Pacing Is Indicated

Class IIa Recommendation (Reasonable):

Permanent pacing is reasonable for marked first-degree AV block (typically PR >300 ms) when symptoms are clearly attributable to the AV block. 2, 1 This includes:

• Symptoms resembling "pseudo-pacemaker syndrome" (fatigue, exertional intolerance) due to loss of AV synchrony 2
• Decreased cardiac output and increased pulmonary capillary wedge pressure from the prolonged PR interval 2

Class III (Not Indicated):

• Permanent pacemaker implantation is not indicated for asymptomatic first-degree AV block. 1
• There is little evidence that pacemakers improve survival in isolated first-degree AV block. 2

Important Clinical Pitfalls

Risk of Progression:

First-degree AV block may not be entirely benign in all patients. 3 A study using insertable cardiac monitors found that 40.5% of patients with baseline first-degree AV block eventually required pacemaker implantation, with 93.3% needing it due to progression to more severe bradycardia or higher-grade block. 3 This suggests first-degree AV block can be a risk marker for intermittent conduction disease. 3

Special Populations Requiring Close Monitoring:

• Neuromuscular diseases: Patients with myotonic dystrophy or Kearns-Sayre syndrome require close surveillance as they may progress to higher-degree block. 1
• Bifascicular block: Monitor for progression, as the combination increases risk. 1
• Structural heart disease: Any underlying cardiac pathology warrants closer follow-up. 1

Cardiology Referral Indications

Refer to cardiology when:

• PR interval >300 ms 1
• Symptoms of fatigue or exercise intolerance clearly related to the conduction delay 1
• Coexisting bundle branch block or bifascicular block 1
• Structural heart disease present 1
• Evidence of progression to higher-degree block on monitoring 1

Prognosis and Patient Education

Most cases of isolated first-degree AV block have excellent prognosis. 1 However, educate patients to report symptoms that might indicate progression: syncope, presyncope, severe fatigue, or exercise intolerance. 1 These warrant immediate re-evaluation for higher-degree block.