What are AV nodal blocking agents?

AV Nodal Blocking Agents

AV nodal blocking agents are medications that slow conduction through the atrioventricular node and include beta-blockers, nondihydropyridine calcium channel blockers (verapamil and diltiazem), digoxin, adenosine, and amiodarone. 1

Primary AV Nodal Blocking Agents

Beta-Blockers

• Beta-blockers antagonize sympathetic tone in nodal tissue, resulting in slowing of AV nodal conduction. 1
• Specific agents include metoprolol, atenolol, propranolol, nadolol, and esmolol. 1
• These agents prolong the AH interval, increase AV nodal refractory periods, and may lengthen the PR interval. 2
• Beta-blockers are particularly effective for rate control both at rest and during exercise. 3

Nondihydropyridine Calcium Channel Blockers

• Verapamil and diltiazem are the two nondihydropyridine calcium channel blockers that effectively block AV nodal conduction. 1
• These agents inhibit the slow inward calcium current, which prolongs conduction and refractoriness in the AV node. 2
• Verapamil and diltiazem have been established as effective in converting supraventricular tachycardia and controlling ventricular rate. 1
• Nifedipine, a dihydropyridine calcium channel blocker, is NOT an AV nodal blocking agent because it cannot be used in doses large enough to affect the AV node without causing excessive vasodilation. 2, 4

Digoxin (Cardiac Glycoside)

• Digoxin slows AV nodal conduction through vagotonic effects on the AV node. 1
• It is generally effective for rate control in persistent atrial fibrillation, particularly when heart failure is present. 1
• Digoxin is less effective as a single agent for acute rate control and does not slow heart rate during exercise as effectively as beta-blockers or calcium channel blockers. 1

Adenosine

• Adenosine is a short-acting AV nodal blocking agent used primarily for acute termination of supraventricular tachycardia. 1
• Its extremely short half-life (seconds) makes it ideal for diagnostic purposes and acute treatment but not for sustained rate control. 1

Amiodarone

• Amiodarone has both sympatholytic and calcium antagonistic properties that depress AV conduction. 1, 5
• The ACC/AHA/HRS guidelines classify amiodarone alongside other drugs with "SA and/or AV nodal-blocking properties." 5
• It may be considered for rate control when other measures are unsuccessful or contraindicated, particularly in patients with systolic heart failure. 5

Critical Contraindications

Wolff-Parkinson-White Syndrome

• AV nodal blocking agents (including adenosine, beta-blockers, calcium channel blockers, and digoxin) are contraindicated in patients with WPW syndrome and pre-excited atrial fibrillation or flutter. 1
• These agents can facilitate antegrade conduction along the accessory pathway, resulting in acceleration of ventricular rate, hypotension, or ventricular fibrillation. 1

Combination Therapy Risks

• Caution is advised to avoid combining AV nodal blocking agents with longer duration of action due to risk of profound bradycardia. 1
• Combination therapy with multiple AV nodal blocking agents (such as amiodarone plus beta-blockers or digoxin) carries high risk of severe bradycardia, third-degree AV block, and asystole. 5

Other Contraindications

• AV block greater than first degree or SA node dysfunction (in absence of pacemaker). 1
• Decompensated systolic heart failure or severe left ventricular dysfunction (particularly for calcium channel blockers). 1, 6
• Hypotension. 1

Clinical Pearls

• The short elimination half-life of adenosine allows for safe follow-up treatment with a calcium channel blocker or beta-blocker if needed. 1
• Beta-blockers are preferred in patients with myocardial ischemia, myocardial infarction, hyperthyroidism, and post-operative states. 7
• Nondihydropyridine calcium channel blockers are preferred in patients with bronchial asthma or chronic obstructive pulmonary disease where beta-blockers should be avoided. 1, 7