What are the treatment options and dosages for Atrioventricular Nodal Reentrant Tachycardia (AVNRT)?

AVNRT Treatment: Drugs and Dosages

For acute AVNRT termination in hemodynamically stable patients, start with vagal maneuvers followed immediately by adenosine 6 mg IV rapid push (can repeat with 12 mg if needed), which terminates AVNRT in approximately 95% of cases. 1

Acute Treatment Algorithm

First-Line: Vagal Maneuvers

• Modified Valsalva maneuver with patient supine: bear down against closed glottis for 10-30 seconds, generating intrathoracic pressure of at least 30-40 mmHg 1, 2
• Modified Valsalva is 2.8-3.8 times more effective than standard technique 2
• Carotid sinus massage: apply steady pressure over carotid sinus for 5-10 seconds after confirming absence of bruit by auscultation 1
• Ice-cold wet towel to face is an alternative vagal maneuver 1
• Overall success rate of vagal maneuvers is approximately 27.7% when switching between techniques 1

Second-Line: Adenosine (Class I Recommendation)

• Initial dose: 6 mg rapid IV push through large vein, followed immediately by saline flush 2, 3
• If unsuccessful: 12 mg rapid IV push (can repeat once) 2
• Alternative dosing: start with 3 mg, then escalate to 6 mg, 9 mg, or 12 mg 4
• Success rate: 90-95% termination of AVNRT 1, 2, 4
• Have cardioversion equipment ready during administration 2

Critical caveat: Adenosine has marginal efficacy in critically ill surgical/trauma patients (only 44% success initially, 34% for relapses), requiring progression to other agents more frequently 5

Third-Line: IV Calcium Channel Blockers or Beta-Blockers (Class IIa Recommendation)

Verapamil

• Initial dose: 0.075-0.1 mg/kg IV (typically 5-10 mg) 4
• Subsequent bolus: 5 mg can be given to maximal total dose of 15-20 mg 4
• Success rate: 80-98% conversion 1, 6
• Particularly effective for AVNRT termination 1

Diltiazem

• IV diltiazem (specific dosing not provided in guidelines, but equally effective to verapamil) 1
• Success rate: 80-98% conversion 1
• More effective than esmolol in head-to-head comparison 1

Beta-Blockers

• Esmolol or metoprolol IV (specific dosing not detailed in guidelines) 1
• Less effective than calcium channel blockers but excellent safety profile 1

Major contraindications for calcium channel blockers/beta-blockers:

• Never give if ventricular tachycardia or pre-excited atrial fibrillation suspected—can precipitate ventricular fibrillation 1, 6
• Avoid in suspected systolic heart failure 1
• Avoid in severe conduction abnormalities or sinus node dysfunction 1

Fourth-Line: IV Amiodarone (Class IIb Recommendation)

• IV amiodarone when other therapies ineffective or contraindicated 1
• Specific dosing not provided in guidelines
• Effective in small cohort studies for AVNRT termination 1
• Long-term toxicity not seen with short-term IV use 1

Oral Agents for Acute Treatment (Class IIb Recommendation)

• Oral beta-blockers, diltiazem, or verapamil may be reasonable, particularly when IV access unavailable 1
• Combination of oral diltiazem plus propranolol demonstrated success in studies 1
• Can be administered in conjunction with vagal maneuvers 1

Synchronized Cardioversion (Class I Recommendation)

• Immediate cardioversion for hemodynamically unstable patients when adenosine/vagal maneuvers fail or not feasible 1, 6
• Initial energy: 50-100 joules for SVT 2
• Also indicated for stable patients when pharmacological therapy fails or contraindicated 1
• Highly effective at terminating AVNRT 1

Ongoing/Chronic Management

First-Line Pharmacological Therapy (Class I Recommendation)

• Oral verapamil or diltiazem for patients not pursuing catheter ablation 1, 6
• Well-tolerated and effective alternatives to ablation 1
• Monitor for bradyarrhythmias and hypotension when initiating 1
• Avoid in systolic heart failure 1

Alternative Chronic Agents

• Digoxin alone or with beta-blockers: effective in approximately 50% of cases, especially when combination proved successful during electrophysiological testing 4
• Class IC agents (flecainide, propafenone): can terminate reentry by lengthening refractory period of fast pathway 4
• Class IA agents (procainamide): alternative option 4

Important warning about flecainide: Proarrhythmic effects occur in 4% of supraventricular arrhythmia patients; therapy should be initiated in hospital for high-risk patients 7

Definitive Therapy: Catheter Ablation (Class I Recommendation)

• Slow pathway ablation is first-line definitive therapy 1
• Success rate: 94.3-98.5% 6
• Potentially curative, eliminating need for chronic pharmacological therapy 1
• Should be considered in patients with poor anterograde fast pathway conduction to avoid AV block 8

Key Clinical Pearls

Relapse prevention: 50% of patients develop relapses after initial conversion in ICU settings; suppressive therapy with calcium channel blockers or beta-blockers essential during period of maximal cardiovascular stress 5

Plasma level monitoring: For chronic oral therapy, therapeutic plasma levels of 0.2-1 mcg/mL may be needed for maximal effect; levels above 0.7-1 mcg/mL associated with higher cardiac adverse events 7

Post-conversion management: Atrial or ventricular premature complexes may occur immediately after conversion; antiarrhythmic drug may be required to prevent acute reinitiation 2