What are the causes and management of complete heart block?

Causes of Complete Heart Block

Complete heart block (third-degree AV block) is most commonly caused by degenerative fibrosis of the conduction system, myocardial ischemia/infarction, or iatrogenic factors following cardiac procedures. 1

Etiology of Complete Heart Block

Degenerative/Idiopathic Causes

• Lev's disease (age-related fibrosis and calcification of the cardiac skeleton)
• Lenègre's disease (progressive fibrosis of the conduction system)
• Congenital heart block

Ischemic Causes

• Acute myocardial infarction (particularly inferior MI)
• Chronic ischemic heart disease with fibrosis

Iatrogenic/Procedural Causes

• Cardiac surgery (especially valve surgery)
• Alcohol septal ablation for hypertrophic cardiomyopathy 1
• Transcatheter aortic valve replacement
• Endomyocardial biopsy (rare complication) 1

Infectious/Inflammatory Causes

• Lyme carditis
• Myocarditis
• Endocarditis
• Cardiac sarcoidosis
• Rheumatic fever

Infiltrative Disorders

• Amyloidosis
• Hemochromatosis
• Scleroderma

Metabolic/Electrolyte Disturbances

• Severe hyperkalemia
• Severe hypothyroidism

Medication-Related

• Beta-blockers
• Calcium channel blockers
• Digoxin toxicity
• Antiarrhythmic drugs (Class I and III)

Structural Heart Disease

• Ventricular septal defect (complication) 1
• Hypertrophic cardiomyopathy
• Cardiac tumors

Clinical Presentation

Complete heart block presents with:

• Bradycardia (typically 20-40 bpm with ventricular escape rhythm, 40-60 bpm with junctional escape)
• Fatigue and reduced exercise capacity
• Dizziness or syncope (Stokes-Adams attacks)
• Dyspnea on exertion
• Heart failure symptoms in some cases

Diagnosis

ECG findings show:

• Complete dissociation between P waves and QRS complexes
• Regular P-P intervals
• Regular R-R intervals
• P rate faster than QRS rate
• QRS morphology depends on escape focus location:
  • Narrow QRS (junctional escape)
  • Wide QRS (ventricular escape)

Management

Acute Management

• For hemodynamically unstable patients:

  • Atropine 0.5-1.0 mg IV (may repeat up to total dose of 1.5-2.0 mg) 2
  • Transcutaneous pacing for immediate support
  • Transvenous temporary pacing for persistent instability 3

• For hemodynamically stable patients:

  • Close monitoring with continuous ECG
  • IV access and preparation for emergency interventions
  • Identify and treat reversible causes 3

Definitive Management

• Permanent pacemaker implantation is indicated for:

  • Symptomatic complete heart block
  • Complete heart block with wide QRS escape rhythm
  • Complete heart block with mean daytime heart rate below 50 bpm
  • Complete heart block with complex ventricular ectopy
  • Complete heart block with ventricular dysfunction 3

• In acute MI with complete heart block:

  • Temporary pacing is indicated if not responsive to medical therapy
  • Permanent pacing is indicated if high-degree AV block persists >72 hours 1, 3

Prognosis

Prognosis depends on:

• Underlying cause
• Escape rhythm stability
• Presence of structural heart disease
• Timely intervention with appropriate pacing

Without pacemaker implantation, patients with symptomatic complete heart block have significantly higher mortality rates, particularly those with wide QRS escape rhythms or Stokes-Adams attacks 4, 5.

Special Considerations

• Pregnancy: Most women with congenital complete heart block can tolerate pregnancy well, but temporary pacing during delivery may be needed if symptoms develop 6
• Athletes: Asymptomatic patients with congenital complete heart block may have normal exercise capacity through compensatory mechanisms 5
• Acute MI: Complete heart block in this setting carries higher risk of cardiogenic shock and mortality 3, 7

Complete heart block requires prompt recognition and appropriate management to prevent adverse outcomes, with permanent pacing being the definitive treatment for most cases.