Diltiazem Dosing for Acute SVT Treatment
For acute SVT in hemodynamically stable patients, administer diltiazem 0.25 mg/kg (approximately 15-20 mg for average adults) IV over 2 minutes, followed by a second dose of 0.35 mg/kg (20-25 mg) after 15 minutes if the first dose fails to convert the rhythm. 1, 2, 3
Initial Bolus Dosing
- First dose: 0.25 mg/kg IV administered over 2 minutes 1, 2, 3
- Second dose (if needed): 0.35 mg/kg IV given 15 minutes after the first dose if no therapeutic response occurs 2, 3, 4
- Expected response time: Conversion typically occurs within 2-3 minutes of administration, with maximal heart rate reduction in 2-7 minutes 3, 4
- Success rate: Diltiazem terminates SVT in 82-100% of patients, depending on the dose used 4, 5, 6
Maintenance Infusion (If Needed)
- Start continuous infusion at 5 mg/hour after successful bolus conversion 2
- Titrate up to 15 mg/hour based on heart rate response 2
- Duration of effect after bolus: Heart rate reduction may last 1-3 hours; after 24-hour infusion, effects may persist 0.5 to >10 hours (median 7 hours) 3
Critical Contraindications - Do Not Use Diltiazem If:
- Pre-excited atrial fibrillation/flutter (WPW syndrome or visible accessory pathway): May cause ventricular fibrillation and hemodynamic collapse 7, 2, 3
- Second or third-degree AV block without pacemaker 2, 3
- Decompensated heart failure or severe LV systolic dysfunction: Negative inotropic effects can worsen hemodynamics 7, 2
- Hypotension or cardiogenic shock 2, 3
- Sick sinus syndrome without pacemaker 2
- Hemodynamically unstable patients: Proceed directly to synchronized cardioversion instead 7, 2
Place in Treatment Algorithm
- First-line: Vagal maneuvers should be attempted first 7, 3
- Second-line: Adenosine is the preferred initial pharmacologic agent due to rapid action and short half-life 1, 2
- Third-line: Diltiazem is an excellent option when adenosine fails or is contraindicated 7, 1, 2
- Diltiazem is more effective than esmolol for SVT termination 7, 5
Monitoring Requirements During Administration
- Continuous ECG monitoring is mandatory throughout administration 2, 3
- Frequent blood pressure measurements during bolus and infusion 2, 3
- Defibrillator and resuscitation equipment must be immediately available 1, 2, 3
Common Adverse Effects and Management
- Hypotension: Most common adverse effect (occurs in 3-7% of patients), usually short-lived but may persist 1-3 hours 3, 4, 8
- Manage with IV fluids or Trendelenburg position; 3.2% of patients require intervention 3
- Bradycardia: May require atropine or temporary pacing if severe 1
- Worsening heart failure in predisposed patients 1
Critical Pitfall to Avoid
Never combine diltiazem with beta-blockers acutely - this combination can cause profound bradycardia and heart block 2
Mechanism of Action
Diltiazem works by slowing AV node conduction, increasing AV node refractoriness, and prolonging the AV nodal effective refractory period 1, 9, 6