Diltiazem for Supraventricular Tachycardia
For acute SVT termination in hemodynamically stable patients, give diltiazem 0.25 mg/kg (15-20 mg for average adult) IV over 2 minutes, followed by a second dose of 0.35 mg/kg (20-25 mg) after 15 minutes if needed. 1, 2
Acute Management Protocol
Initial Dosing
- First bolus: 0.25 mg/kg (approximately 15-20 mg for average 70 kg patient) administered IV over 2 minutes 1, 2
- Second bolus: If inadequate response after 15 minutes, give 0.35 mg/kg (approximately 20-25 mg) IV over 2 minutes 1, 2
- Success rate: Diltiazem terminates SVT in 64-98% of hemodynamically stable patients 1
- Time to conversion: Median 2-3 minutes after infusion initiation 3, 4
Continuous Infusion (for rate control)
- Initial rate: 10 mg/hour after successful bolus conversion 1, 2
- Titration: May increase by 5 mg/hour increments up to maximum 15 mg/hour 1, 2
- Duration: Maximum 24 hours (longer durations not studied) 2
- Some patients maintain response at 5 mg/hour 2
Oral Therapy for Ongoing Management
For patients declining catheter ablation or requiring chronic suppression, oral diltiazem is a Class I recommendation. 1
- Starting dose: 120 mg daily 5
- Maximum dose: 480 mg daily (proven effective in randomized trials) 5
- Diltiazem is well-tolerated and effective as an alternative to ablation for long-term AVNRT management 1
Critical Safety Considerations
Absolute Contraindications
Do not give diltiazem if any of the following are present: 1, 5
- Wide-complex tachycardia (unless proven supraventricular origin) - risk of hemodynamic collapse if ventricular tachycardia 1
- Pre-excited atrial fibrillation/flutter (WPW syndrome with AF) - may accelerate ventricular rate and cause ventricular fibrillation 1, 5
- Systolic heart failure or severe LV dysfunction - negative inotropic effects worsen cardiac output 1, 5
- Hypotension - diltiazem causes further blood pressure reduction 5
- AV block greater than first degree (without pacemaker) 5
Common Adverse Effects
- Hypotension: Most frequent side effect, occurring in approximately 6-11% of patients 5, 3
- Slow infusion over 20 minutes may reduce hypotension risk 1
- Bradycardia: Monitor for excessive rate slowing, especially with concurrent beta-blocker use 1
Clinical Pearls
When to Use Diltiazem
- Second-line agent after adenosine fails or when adenosine is contraindicated 1, 5
- Preferred over beta-blockers for acute SVT termination - diltiazem more effective than esmolol in head-to-head comparison 1, 6
- Useful for recurrent SVT after adenosine conversion due to longer duration of action 1
- Particularly effective when AV node is part of reentrant circuit (AVNRT, orthodromic AVRT) 4
Drug Interactions
Avoid sequential administration with beta-blockers - the longer half-life of both agents causes overlapping effects and risk of profound bradycardia 1
Mechanism
Diltiazem works by slowing AV nodal conduction and increasing AV nodal refractoriness, terminating reentrant tachycardias dependent on the AV node 5, 4
Efficacy by SVT Type
- AVNRT: 100% conversion rate in studies 4
- AVRT (orthodromic): 81-84% conversion rate 3, 4
- Atrial fibrillation/flutter: Effective for rate control but lower conversion rates 7