Management of First-Degree Atrioventricular Block

First-degree AV block is generally benign and requires no treatment in asymptomatic patients with PR intervals less than 0.30 seconds. 1, 2

Definition and Diagnosis

First-degree AV block is defined as a prolongation of the PR interval beyond 0.20 seconds (200 ms) on ECG, representing a delay in AV conduction 1, 2
It typically occurs at the level of the AV node, though can occasionally be located within the His-Purkinje system 2

Assess for symptoms such as fatigue, exercise intolerance, or symptoms similar to pacemaker syndrome 1
Evaluate for signs of poor perfusion that could be attributed to bradycardia 1
Consider hemodynamic compromise (hypotension, increased wedge pressure) in patients with first-degree AV block 1
PR intervals of 0.20-0.30 seconds are usually asymptomatic 1
PR intervals >0.30 seconds may cause symptoms due to inadequate timing of atrial and ventricular contractions (similar to pacemaker syndrome) 1, 3

No treatment is required for isolated first-degree AV block 1, 2
Consider ambulatory ECG monitoring if there is concern about progression to higher-degree block 2
Exercise testing may be useful to determine if the PR interval shortens appropriately during exercise in benign cases 1, 4

Identify and treat reversible causes:
- Medications (beta-blockers, calcium channel blockers, digoxin) 1, 2
- Electrolyte abnormalities 1
- Infectious diseases (e.g., Lyme disease) 1
- Infiltrative diseases (e.g., sarcoidosis, amyloidosis) 1
For patients with marked first-degree AV block (PR >0.30 seconds):
- Permanent pacemaker implantation is reasonable for patients with symptoms similar to pacemaker syndrome or hemodynamic compromise (Class IIa recommendation) 1, 2
- Consider treadmill stress testing to assess if symptoms worsen with exercise when PR interval cannot adapt appropriately 4
For acute management of symptomatic bradycardia:
- Atropine (0.5 mg IV every 3-5 minutes to a maximum of 3 mg) may be considered for symptomatic bradycardia associated with first-degree AV block at the level of the AV node 1
- Caution: doses <0.5 mg may paradoxically result in further slowing of heart rate 1
- Atropine should be used with caution in acute MI due to protective effect of parasympathetic tone against ventricular fibrillation 2

Consider more intensive monitoring for patients with evidence of structural heart disease 1
Echocardiography should be considered if there are signs of structural heart disease or if the QRS complex is abnormal 1

RBBB with first-degree AV block in acute myocardial infarction warrants temporary transvenous pacing 2
Outside of acute MI, persistent first-degree AV block with bundle branch block that is old or of indeterminate age does not necessarily require permanent pacing 2

Consider permanent pacing due to unpredictable progression of conduction disease 1

First-degree AV block is not always benign; recent research suggests it may be a risk marker for more severe intermittent conduction disease 5
In one study with insertable cardiac monitors, 40.5% of patients with first-degree AV block required pacemaker implantation during follow-up due to progression to higher-grade block or detection of more severe bradycardia 5
Risk factors for progression include PR interval >300 ms, coexisting bundle branch block, and neuromuscular diseases associated with conduction disorders 2

Avoid unnecessary pacemaker implantation for isolated, asymptomatic first-degree AV block 2
Consider medication effects as potential causes of reversible first-degree AV block before pursuing invasive interventions 2
Don't overlook the possibility of pseudopacemaker syndrome in patients with marked first-degree AV block who present with symptoms similar to pacemaker syndrome 6