What are the indications for pacemaker implantation in patients with third degree (complete) heart block?

Indications for Pacemaker Implantation in Third Degree Heart Block

Permanent pacemaker implantation is indicated for all patients with third-degree (complete) heart block associated with symptomatic bradycardia, regardless of anatomical level of block. 1

Class I Indications (Definite Indications)

Symptomatic Patients

• Third-degree AV block at any anatomic level with:
  • Bradycardia causing symptoms (including heart failure) 1
  • Ventricular arrhythmias presumed due to AV block 1
  • Need for medications causing symptomatic bradycardia 1

Asymptomatic Patients

• Third-degree AV block with any of the following:
  • Documented periods of asystole ≥3.0 seconds 1
  • Any escape rate <40 bpm in awake patients 1
  • Escape rhythm below the AV node 1
  • Atrial fibrillation with bradycardia and ≥1 pause of 5 seconds or longer 1
  • Average awake ventricular rates ≥40 bpm with cardiomegaly or LV dysfunction 1
  • Average awake ventricular rates ≥40 bpm if block is below the AV node 1

Special Circumstances

• Third-degree AV block:
  • After catheter ablation of the AV junction 1
  • Associated with postoperative AV block not expected to resolve 1
  • During exercise in the absence of myocardial ischemia 1
  • Associated with neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome, limb-girdle muscular dystrophy) 1

Class IIa Indications (Reasonable)

• Persistent third-degree AV block with escape rate >40 bpm in asymptomatic adults without cardiomegaly 1

Clinical Considerations

Anatomical Level of Block

The site of block affects prognosis and pacing indications:

• Infra-nodal block (below the AV node) carries worse prognosis and more strongly indicates pacing, even in asymptomatic patients 1
• Block during exercise (if not due to ischemia) typically indicates His-Purkinje disease and warrants pacing 1

Progression Risk

Certain conditions have high risk of progression to complete heart block:

• Patients with bifascicular block (especially RBBB + left anterior hemiblock) have increased risk of progression to complete heart block 2
• Neuromuscular diseases may have unpredictable progression of conduction disease 3

Post-Surgical Considerations

• Approximately 1.4% of cardiac surgery patients require permanent pacemaker implantation 4
• Early pacemaker implantation (around day 5 post-surgery) may be appropriate for high-risk patients who remain pacemaker dependent after surgery 4
• Predictors for pacemaker requirement after cardiac surgery include pre-existing left bundle branch block and aortic valve replacement 4

Contraindications

Permanent pacemaker implantation is not indicated for:

• AV block expected to resolve (drug toxicity, Lyme disease, transient vagal tone increases, sleep apnea) 1

Important Caveats

• Even asymptomatic patients with third-degree AV block often require pacing due to risk of sudden death
• The origin of the escape rhythm (AV node, His bundle, or infra-His) is more critical for safety than just the escape rate 1
• Approximately 63% of patients requiring pacemakers after cardiac surgery remain pacemaker-dependent at long-term follow-up 4
• In patients with neuromuscular diseases like myotonic dystrophy, consider ICDs rather than pacemakers due to risk of ventricular arrhythmias and sudden death 3

The decision to implant a pacemaker should be made promptly when indications are met, as delays may increase morbidity and mortality in patients with complete heart block.