What medications worsen atrioventricular (AV) conduction?

Medications That Worsen AV Conduction

Beta-blockers, calcium channel blockers (particularly non-dihydropyridines like verapamil and diltiazem), digoxin, amiodarone, and Class IC antiarrhythmic drugs are the primary medications that worsen AV conduction and should be used with caution in patients with existing conduction abnormalities.

AV Nodal Blocking Medications

Beta-Blockers

• Metoprolol, propranolol, esmolol, and other beta-blockers slow AV nodal conduction by:
  • Antagonizing sympathetic tone in nodal tissue 1
  • Increasing AV nodal refractory period 2
  • Prolonging PR interval on ECG 1
• Side effects include:
  • Bradycardia
  • Heart block (usually first-degree)
  • Hypotension
  • Worsening heart failure 2, 1

Non-Dihydropyridine Calcium Channel Blockers

• Verapamil and diltiazem:
  • Inhibit slow inward calcium current in AV node 3
  • Prolong AV nodal conduction time and refractoriness 2, 3
  • Can cause:
    • First-degree AV block (most common)
    • Higher-degree blocks (less common but possible) 2, 3
  • Contraindicated in:
    • Decompensated heart failure
    • Pre-existing AV block greater than first degree
    • Severe LV dysfunction 2

Cardiac Glycosides

• Digoxin:
  • Slows AV nodal conduction
  • Can cause heart block, especially at toxic levels
  • Particularly problematic when combined with other AV nodal blocking agents 2
  • Not recommended as sole agent for rate control in paroxysmal AF 2

Class III Antiarrhythmic Agents

• Amiodarone:
  • Has negative chronotropic properties
  • Can cause significant bradycardia and AV block
  • May interact with other AV nodal blocking drugs 2
  • Should be used with caution when other measures fail 2

Class IC Antiarrhythmic Agents

• Flecainide and propafenone:
  • Can worsen or precipitate AV conduction disorders
  • Contraindicated in patients with pre-existing sinus or AV conduction disease (without pacemaker) 2
  • Propafenone has mild beta-blocking effects that can further slow AV conduction 2

Special Considerations

Combination Therapy Risks

• Combining AV nodal blocking agents significantly increases risk of severe bradycardia and heart block
• Beta-blockers combined with non-dihydropyridine calcium channel blockers pose particular risk 4
• Digoxin combined with beta-blockers produces synergistic effect on AV node 2

Wolff-Parkinson-White (WPW) Syndrome

• AV nodal blocking agents are absolutely contraindicated in patients with WPW syndrome who have pre-excited atrial fibrillation or flutter 2, 5
• These medications can:
  • Facilitate antegrade conduction through accessory pathway
  • Accelerate ventricular response
  • Precipitate ventricular fibrillation 2, 5
• Contraindicated medications in WPW with pre-excited AF include:
  • Beta-blockers
  • Digoxin
  • Non-dihydropyridine calcium channel blockers
  • Adenosine 5

Patients at Highest Risk

• Elderly patients
• Those with pre-existing conduction abnormalities
• Patients with structural heart disease
• Those with renal dysfunction (especially with digoxin)
• Patients receiving multiple AV nodal blocking agents 2, 6

Clinical Implications

• Monitor ECG for PR interval prolongation when initiating these medications
• Start with lower doses in high-risk patients
• Be cautious when combining AV nodal blocking agents
• Consider temporary discontinuation of these medications when evaluating for permanent pacemaker need, as approximately 15% of AV blocks are truly drug-induced 6
• In patients with heart failure, beta-blockers should be initiated at low doses with careful titration 2

Remember that while these medications can worsen AV conduction, they are often essential therapies for many cardiovascular conditions, and their benefits frequently outweigh the risks when used appropriately with proper monitoring.