What is the recommended dosing regimen of diltiazem (initial bolus, repeat bolus, and maintenance infusion) for acute paroxysmal supraventricular tachycardia in adults?

Diltiazem Dosing for Acute PSVT in Adults

For acute PSVT management in hemodynamically stable adults, administer diltiazem 0.25 mg/kg (approximately 15-20 mg) IV over 2 minutes, followed by a second dose of 0.35 mg/kg (approximately 20-25 mg) after 15 minutes if the initial dose fails to terminate the arrhythmia or adequately control ventricular rate. 1, 2

Initial Bolus Dosing

• First dose: 0.25 mg/kg IV administered over 2 minutes 1, 2, 3

  • For an average 70-80 kg adult, this equals approximately 15-20 mg 1
  • Conversion typically occurs within 2-3 minutes after infusion completion in responding patients 3, 4

• Second dose (if needed): 0.35 mg/kg IV given 15 minutes after the first dose if no therapeutic response 2, 3

  • This equals approximately 20-25 mg for average adults 2
  • The American College of Cardiology recommends this repeat dosing strategy for non-responders 2

Maintenance Infusion

• Start at 5 mg/hour and titrate up to 15 mg/hour based on heart rate response 2
• Continuous infusion maintains rate control after successful conversion 2

Critical Pre-Administration Considerations

Absolute contraindications that must be ruled out before giving diltiazem:

• Pre-excited atrial fibrillation/flutter (WPW syndrome): Diltiazem can accelerate ventricular response and cause hemodynamic collapse or ventricular fibrillation 5, 2
• Hemodynamic instability: Proceed directly to synchronized cardioversion instead 5, 2
• Decompensated heart failure or severe LV dysfunction: Negative inotropic effects can worsen heart failure 5, 1, 2
• Second or third-degree AV block without pacemaker 2
• Hypotension or cardiogenic shock 1, 2
• Sick sinus syndrome without pacemaker 2

Treatment Algorithm

1. First-line: Attempt vagal maneuvers 5
2. Second-line: Adenosine is preferred as first pharmacologic agent due to rapid action and short half-life 1, 2
3. Third-line: If adenosine fails or is contraindicated, diltiazem is an excellent alternative 5, 1
4. Last resort: Synchronized cardioversion if medications fail 5

Efficacy Data

• Conversion rates: 82-100% success in clinical trials, with higher rates (90-100%) at the 0.25 mg/kg dose 3, 6, 4
• Time to conversion: Median 2-5 minutes after infusion initiation 3, 6, 4
• Mechanism-specific efficacy: 100% conversion in AV nodal reentrant tachycardia vs. 81% in AV reciprocating tachycardia 3

Monitoring Requirements

Essential monitoring during administration:

• Continuous ECG monitoring throughout drug administration 2
• Frequent blood pressure measurements (hypotension occurs in 6-7% of patients) 7, 4
• Defibrillator and resuscitation equipment immediately available 1, 2

Common Pitfalls to Avoid

• Do not combine with beta-blockers acutely: Risk of profound bradycardia and heart block 2
• Avoid slow infusion in unstable patients: If hemodynamically unstable, skip medications entirely and cardiovert 2
• Do not use if uncertain about rhythm mechanism: Must rule out VT or pre-excited AF first, as these can deteriorate with diltiazem 5

Management of Adverse Effects

Most common side effects:

• Hypotension (most common): Usually responds to IV fluids; occurred in 2-7% of patients in trials 1, 7, 4, 8
• Bradycardia: May require atropine or temporary pacing if severe 1, 7
• Worsening heart failure in predisposed patients 1

Side effects typically reverse rapidly after cessation of diltiazem 7

Mechanism of Action

Diltiazem terminates PSVT by slowing AV node conduction and increasing AV node refractoriness, breaking the reentrant circuit 1, 3