What medications should be avoided in patients with atrioventricular (AV) block?

Medications to Avoid in AV Block

Patients with AV block should strictly avoid AV nodal blocking agents including beta-blockers, non-dihydropyridine calcium channel blockers (verapamil, diltiazem), digoxin, and certain antiarrhythmic drugs, as these medications can worsen conduction abnormalities and precipitate complete heart block or severe bradycardia. 1, 2

Primary Medications to Avoid

Beta-Blockers

• All beta-blockers have negative dromotropic effects on the AV node and prolong AV nodal conduction time, making them dangerous in pre-existing AV conduction abnormalities 1
• This includes metoprolol, atenolol, propranolol, carvedilol, bisoprolol, and esmolol 3, 2
• The combination of beta-blockers with other AV nodal blocking agents carries particularly high risk of worsening AV block 1

Non-Dihydropyridine Calcium Channel Blockers

• Verapamil and diltiazem are contraindicated as they significantly slow AV conduction and can cause heart block 1, 2
• The FDA label for verapamil specifically warns that it can cause asymptomatic first-degree AV block and transient bradycardia, with higher degrees of AV block observed in 0.8% of patients 4
• Verapamil's effect on AV conduction is correlated with plasma concentrations, especially during early titration 4
• Marked first-degree block or progressive development to second- or third-degree AV block requires dose reduction or discontinuation 4

Digoxin

• Digoxin should be avoided as it further slows AV conduction and can worsen the block 1
• If digoxin must be used, dose reduction and careful monitoring are required 1
• Digoxin can cause bradycardia and heart block, especially in patients with pre-existing conduction system disease 2

Class I Antiarrhythmic Agents

• Flecainide and propafenone should be avoided as they may worsen conduction disorders 1
• These agents are contraindicated in patients with sinus or AV conduction disease 2
• Flecainide and propafenone can have additive effects on AV conduction when combined with other agents 4

Class III Antiarrhythmic Agents

• Amiodarone should be used with extreme caution due to its potential to cause bradycardia and worsen AV block 1, 2
• Sotalol and dofetilide can also cause significant bradycardia 2
• The 2014 AHA/ACC/HRS guidelines note that in patients with pre-excitation and atrial fibrillation, intravenous amiodarone should not be administered as it may increase ventricular response and result in ventricular fibrillation 3

Other Medications

• Ivabradine is absolutely contraindicated in patients with second-degree AV block, as it directly inhibits the sinoatrial node 1, 2
• Concurrent use of verapamil with ivabradine increases exposure and may exacerbate bradycardia and conduction disturbances 4
• S1P receptor modulators (like ozanimod) should be used with caution in Mobitz type I 1

Critical Drug Combinations to Avoid

Multiple AV Nodal Blocking Agents

• Combination therapy with multiple AV nodal blocking agents (e.g., beta-blocker plus calcium channel blocker) carries particularly high risk of worsening AV block 1
• Concomitant therapy with beta-blockers and verapamil may result in additive negative effects on heart rate, AV conduction, and cardiac contractility 4
• There have been reports of excessive bradycardia and complete heart block when this combination has been used 4, 5
• Asymptomatic bradycardia (36 beats/min) with wandering atrial pacemaker has been observed with combined timolol eyedrops and oral verapamil 4

Specific High-Risk Combinations

• Verapamil with beta-blockers should be used only with caution and close monitoring, if at all 4, 6
• The combination of verapamil and beta-blockers is not advised due to risk of AV block and bradycardia 6
• Higher-dose diltiazem with beta-blockers is also not advised 6
• Verapamil with disopyramide: disopyramide should not be administered within 48 hours before or 24 hours after verapamil 4

Special Considerations by AV Block Type

Mobitz Type I (Wenckebach)

• Mobitz type I is characterized by progressive PR interval prolongation until a beat is not conducted, and the block is usually at the AV node level 1
• It is often transient and asymptomatic, commonly associated with inferior wall MI and usually resolves spontaneously 1
• If medication-induced Mobitz type I block occurs, the offending agent should be discontinued immediately 1
• Permanent pacing is generally not indicated unless symptomatic and unresponsive to medication discontinuation 1

Higher-Degree AV Block

• In second-degree Mobitz type II or third-degree AV block, all AV nodal blocking agents are absolutely contraindicated
• These patients typically require pacing rather than medication management

Management of Drug-Induced AV Block

Acute Management

• If symptomatic AV block with hemodynamic compromise occurs, atropine (0.5 mg IV every 3-5 minutes to maximum 3 mg) is first-line treatment 1
• Doses of atropine less than 0.5 mg may paradoxically result in further slowing of heart rate 1
• Isoproterenol can be used when atropine is ineffective, but should be avoided in settings of coronary ischemia 2
• Temporary pacing may be indicated for medically refractory symptomatic or hemodynamically significant bradycardia 1, 2

Long-Term Management

• Discontinue all offending AV nodal blocking agents 1
• Reassess the need for these medications and consider alternative therapies that do not affect AV conduction
• Monitor ECG for resolution of conduction abnormalities after drug discontinuation

Common Clinical Pitfalls

Pre-Excitation Syndromes (WPW)

• In patients with pre-excitation and atrial fibrillation, digoxin, non-dihydropyridine calcium channel blockers, and amiodarone should never be administered as they may increase ventricular response and result in ventricular fibrillation 3
• These drugs are selective AV node blockers without slowing conduction through the accessory pathway, leading to increased transmission preferentially through the accessory pathway 7

Heart Failure Patients

• Non-dihydropyridine calcium channel blockers should not be used in decompensated heart failure as they may lead to further hemodynamic compromise 3
• Verapamil should be avoided in patients with severe left ventricular dysfunction (ejection fraction <30%) or moderate to severe symptoms of cardiac failure 4

Monitoring Requirements

• When AV nodal blocking agents cannot be avoided, careful monitoring for abnormal prolongation of the PR interval or other signs of excessive pharmacologic effects is mandatory 4
• Periodic ECG monitoring is essential to detect progression of AV block 4