What medications can cause atrioventricular (AV) block?

Medications That Cause AV Block

Beta-blockers, calcium channel blockers (particularly verapamil and diltiazem), digoxin, and certain antiarrhythmic medications are the most common medications that cause AV block by slowing conduction through the AV node. 1, 2, 3

Common Medication Classes That Cause AV Block

1. Beta-Blockers

• Mechanism: Antagonize sympathetic tone in nodal tissue, resulting in slowing of AV conduction
• Examples:
  • Metoprolol
  • Atenolol
  • Propranolol
  • Nadolol
  • Carvedilol
• Risk factors: Pre-existing conduction disease, elderly patients, concomitant use with other AV nodal blocking agents 1, 4

2. Non-Dihydropyridine Calcium Channel Blockers

• Mechanism: Inhibit calcium influx across cell membranes in the AV node, prolonging refractory period
• Examples:
  • Verapamil: Potent AV nodal blocker with significant risk of AV block
  • Diltiazem: Similar but slightly less potent than verapamil
• Risk factors: Pre-existing AV conduction disease, concomitant use with beta-blockers 1, 2

3. Cardiac Glycosides

• Mechanism: Increase vagal tone and directly depress AV nodal conduction
• Example: Digoxin
• Risk factors: Renal dysfunction, electrolyte abnormalities (especially hypokalemia), concomitant use with other AV nodal blocking agents 1, 5

4. Class I Antiarrhythmic Agents

• Mechanism: Sodium channel blockade affecting cardiac conduction
• Examples:
  • Flecainide
  • Propafenone
  • Disopyramide
  • Procainamide
• Risk factors: Pre-existing conduction disease, structural heart disease 1

5. Class III Antiarrhythmic Agents

• Mechanism: Potassium channel blockade prolonging repolarization
• Examples:
  • Amiodarone
  • Sotalol (also has beta-blocking properties)
• Risk factors: Pre-existing QT prolongation, electrolyte abnormalities 1

High-Risk Drug Combinations

1. Beta-blocker + Non-dihydropyridine calcium channel blocker

   • Particularly dangerous combination with additive effects on AV conduction
   • Can cause profound bradycardia, heart block, and cardiovascular collapse 1, 3

2. Digoxin + Beta-blocker or calcium channel blocker

   • Synergistic effect on slowing AV conduction
   • Requires dose reduction (30-50% reduction of digoxin when combined with amiodarone) 1, 6

3. Multiple AV nodal blocking agents

   • Risk increases with each additional agent
   • Particular caution with triple therapy (beta-blocker + calcium channel blocker + digoxin) 1

Clinical Considerations

• Persistence vs. Reversibility: While AV block is commonly associated with medications, studies show that only about 15-41% of cases are truly caused by drugs and completely resolve after drug discontinuation 7, 5

• Recurrence Risk: Even when AV block resolves after drug discontinuation, approximately 27-56% of patients experience recurrence of AV block despite discontinuation of the culprit drug 7, 5

• Medication-Specific Differences:

  • Carvedilol-induced AV block typically resolves after discontinuation and rarely recurs
  • Metoprolol-induced AV block more commonly persists or recurs despite drug discontinuation
  • Digoxin-induced AV block usually improves after withdrawal of the drug 5

• Pacemaker Requirement: Approximately half of patients with drug-induced AV block ultimately require permanent pacemaker implantation 5

Monitoring and Prevention

1. High-Risk Patients:

   • Elderly patients
   • Pre-existing conduction disease
   • Renal or hepatic dysfunction
   • Multiple AV nodal blocking agents
   • Electrolyte abnormalities

2. ECG Monitoring:

   • Baseline ECG before starting AV nodal blocking agents
   • Follow-up ECG after dose increases or addition of other AV nodal blocking agents
   • Monitor for PR interval prolongation as early warning sign

3. Pharmacological Testing:

   • In patients with bundle branch block, pharmacological stress testing with class IA antiarrhythmic agents (ajmaline, procainamide, disopyramide) can identify those at high risk for developing AV block 1

Remember that drug-induced AV block is a serious condition that can lead to significant morbidity and mortality if not properly recognized and managed. Prompt identification of the culprit medication and appropriate management are essential.