What is the role of diltiazem infusion in the management of supraventricular tachycardia (SVT)?

Role of Diltiazem Infusion in SVT Management

Intravenous diltiazem is highly effective for acute treatment in hemodynamically stable patients with SVT, with success rates of 80-98% for terminating the tachycardia. 1

Acute Management Algorithm for SVT

For Hemodynamically Unstable Patients:

1. Synchronized cardioversion (Class I, Level B-NR) - First-line treatment for hemodynamically unstable SVT 1
   • Perform when adenosine and vagal maneuvers fail or are not feasible
   • Highly effective in restoring sinus rhythm

For Hemodynamically Stable Patients:

1. Vagal maneuvers (Class I, Level B-R) - First-line treatment 2
2. Adenosine IV (Class I, Level B-R) - Second-line treatment 1
   • Rapidly terminates AVNRT in approximately 95% of patients
   • Short half-life with minimal prolonged side effects
3. IV diltiazem (Class IIa, Level B-R) - Third-line treatment 1, 3
   • Dosing: 0.25 mg/kg IV bolus over 2 minutes 4, 5
   • May be followed by continuous infusion if needed 3
   • Particularly effective in converting AVNRT to sinus rhythm
   • Success rates of 82-100% in clinical studies 4, 5, 6
4. IV beta blockers (Class IIa, Level B-R) - Alternative third-line treatment 1
   • Less effective than diltiazem (25% vs 100% conversion rate in comparative studies) 5
   • Consider when diltiazem is contraindicated
5. Synchronized cardioversion - Fourth-line treatment when pharmacological therapy fails 1

Important Considerations for Diltiazem Use

Efficacy:

• Diltiazem works by inhibiting calcium influx during cardiac membrane depolarization 3
• Exhibits frequency-dependent effects on AV nodal conduction, selectively reducing heart rate during tachycardias 3
• In comparative studies, diltiazem (0.25 mg/kg) demonstrated superior efficacy to esmolol (0.5 mg/kg) for terminating PSVT (100% vs 25% success rate) 5
• When first bolus is ineffective, a second bolus after 5 minutes often succeeds 5

Safety Profile:

• Most common adverse effect is hypotension (approximately 11% of patients) 4
• Symptoms related to hypotension occur in only about 6% of cases 4
• Bradycardia may occur, particularly in elderly patients 7
• Side effects typically resolve quickly after cessation of the drug 7

Contraindications:

• Do not use in patients with:
  • Ventricular tachycardia or pre-excited atrial fibrillation (e.g., WPW syndrome) 1, 3
  • Systolic heart failure 1
  • Hemodynamic instability 3
  • Accessory bypass tract 3

Monitoring Requirements:

• Continuous ECG monitoring during administration 3
• Frequent blood pressure measurements 3
• Defibrillator and emergency equipment should be readily available 3

Long-term Management

For patients with recurrent SVT who are not candidates for catheter ablation:

• Oral diltiazem or verapamil is recommended (Class I, Level B-R) 1
• Well-tolerated and effective for ongoing treatment of AVNRT 1
• Oral diltiazem (90 mg every 8 hours) has shown significant reduction in SVT recurrence 8
• Response to IV diltiazem may predict subsequent response to oral therapy 8

Clinical Pearls

• Response to diltiazem usually occurs within 3 minutes, with maximal heart rate reduction in 2-7 minutes 3
• Heart rate reduction may last 1-3 hours after bolus administration 3
• During continuous infusion, 83% of patients maintain at least 20% heart rate reduction 3
• When transitioning from IV to oral therapy, response to IV diltiazem predicts subsequent clinical response to oral diltiazem 8

Remember that while diltiazem is highly effective for SVT, proper patient selection is crucial to avoid potentially dangerous outcomes in contraindicated conditions.