What are the recommended AV (atrioventricular) nodal blocking agents for managing supraventricular tachycardias?

AV Nodal Blocking Agents for Supraventricular Tachycardia

For acute management of hemodynamically stable SVT, adenosine is the first-line AV nodal blocking agent after vagal maneuvers, followed by IV diltiazem or verapamil if adenosine fails, with IV beta-blockers as reasonable alternatives. 1

Acute Management Algorithm

First-Line: Adenosine

• Adenosine terminates 90-95% of AVNRT episodes and serves both therapeutic and diagnostic purposes 2, 3
• Administer 6 mg rapid IV push via large peripheral vein, followed immediately by 20 mL saline flush 4
• If unsuccessful after 1-2 minutes, give 12 mg rapid IV push; may repeat 12 mg dose once more if needed 1
• Peak therapeutic effects occur within 3-5 minutes, with plasma half-life of less than 10 seconds 5, 6
• Have cardioversion equipment ready during administration due to risk of transient arrhythmias 3, 7

Second-Line: Calcium Channel Blockers

IV diltiazem or verapamil achieve 80-98% conversion rates for hemodynamically stable SVT and are more effective than beta-blockers 2, 4

Verapamil Dosing:

• Give 2.5-5 mg IV bolus over 2 minutes (over 3 minutes in elderly patients) 1
• If no response and no adverse effects, repeat with 5-10 mg every 15-30 minutes to total dose of 20 mg 1
• Alternative regimen: 5 mg bolus every 15 minutes to total dose of 30 mg 1

Diltiazem Dosing:

• Give 15-20 mg (0.25 mg/kg) IV over 2 minutes 1
• If needed after 15 minutes, give additional 20-25 mg (0.35 mg/kg) 1
• Maintenance infusion: 5-15 mg/hour, titrated to heart rate 1

Third-Line: Beta-Blockers

• IV beta-blockers (metoprolol, atenolol, esmolol) are reasonable alternatives with excellent safety profile, though less effective than diltiazem 2, 4
• These agents antagonize sympathetic tone in nodal tissue, slowing AV conduction 1
• Use with caution in obstructive pulmonary disease or congestive heart failure 1

Long-Term Management

Oral beta-blockers, diltiazem, or verapamil are first-line for ongoing management in patients with symptomatic SVT who do not have ventricular pre-excitation 1

• Oral verapamil or diltiazem can be used for patients not pursuing catheter ablation 2, 3
• Catheter ablation remains the most effective long-term therapy with 94.3-98.5% success rates 2, 3

Critical Contraindications and Warnings

Never Use AV Nodal Blockers In:

• Pre-excited atrial fibrillation or flutter (Wolff-Parkinson-White with AF)—may precipitate ventricular fibrillation 1, 4
• Wide-complex tachycardia of uncertain origin—assume ventricular tachycardia until proven otherwise 4
• Hemodynamically unstable patients—proceed directly to synchronized cardioversion 4

Verapamil-Specific Contraindications:

• Impaired ventricular function or heart failure 1
• Wide-complex tachycardias 1
• Should only be given for narrow-complex reentry SVT or arrhythmias known with certainty to be supraventricular 1

Adenosine-Specific Warnings:

• Second- or third-degree AV block (except with functioning pacemaker) 7
• Sinus node disease or symptomatic bradycardia (except with functioning pacemaker) 7
• Known bronchoconstrictive or bronchospastic lung disease (e.g., asthma) 7
• Fatal cardiac arrest, sustained ventricular tachycardia, and myocardial infarction have occurred—avoid in acute myocardial ischemia 7

Important Drug Interactions

• Methylxanthines (caffeine, aminophylline, theophylline) interfere with adenosine activity and may increase seizure risk 7
• Dipyridamole and other nucleoside transport inhibitors increase adenosine activity 7
• Avoid combining AV nodal blocking agents with longer duration of action (e.g., verapamil followed by beta-blocker)—can cause profound bradycardia 1
• Adenosine's short half-life allows safe follow-up with calcium channel blockers or beta-blockers if needed 1

Common Pitfalls to Avoid

• Do not use AV nodal blockers if VT or pre-excited atrial fibrillation is suspected—this can precipitate ventricular fibrillation 2, 4
• Ensure rapid bolus administration of adenosine via large peripheral vein with immediate saline flush—slow administration reduces efficacy 4
• Recognize that adenosine commonly produces transient chest discomfort, dyspnea, and flushing lasting less than 1 minute—these are expected and self-limited 8, 6
• Monitor for approximately 6% incidence of AV block with adenosine (3% first-degree, 3% second-degree, 0.8% third-degree) 7
• Be prepared for new-onset atrial fibrillation with adenosine, which typically begins 1.5-3 minutes after initiation and spontaneously converts within 15 seconds to 6 hours 7