Bolus Dose of Diltiazem (Cardizem) for SVT Management
The recommended bolus dose of diltiazem (Cardizem) for acute management of supraventricular tachycardia is 0.25 mg/kg IV administered over 2 minutes. 1, 2
Dosing Protocol for Diltiazem in SVT
Initial Bolus Dose
Follow-up Dosing (if initial dose is inadequate)
- After 15 minutes, a second bolus of 0.35 mg/kg IV over 2 minutes may be administered (approximately 25 mg for an average adult) 1, 2
- Some patients may respond to a lower initial dose of 0.15 mg/kg, though the duration of action may be shorter 2
Maintenance Infusion
- Following successful bolus administration, continuous IV infusion can be initiated at 5-10 mg/hour
- The infusion rate may be increased in 5 mg/hour increments up to 15 mg/hour as needed
- Infusion can be maintained for up to 24 hours 2
Efficacy Evidence
Diltiazem has demonstrated excellent efficacy in terminating SVT:
- 100% conversion rate with 0.25 mg/kg dose in controlled studies 3
- Superior to esmolol for SVT termination (100% vs 25% efficacy) 4
- Effective in both AV nodal reentrant tachycardia (100% conversion) and AV reciprocating tachycardia (81% conversion) 5
Mechanism of Action
Diltiazem terminates SVT by:
- Prolonging refractoriness in the AV node
- Slowing conduction through the AV node
- Interrupting reentrant circuits that involve the AV node 5, 6
Precautions and Contraindications
Diltiazem should be avoided in patients with:
- AV block greater than first degree or SA node dysfunction (without pacemaker)
- Wolff-Parkinson-White syndrome with atrial fibrillation/flutter
- Hypotension
- Decompensated systolic heart failure/LV dysfunction
- Cardiogenic shock
- Significant hepatic or renal dysfunction 1
Potential Adverse Effects
- Hypotension (most common, occurs in approximately 11% of patients)
- Bradycardia
- Worsening heart failure in patients with pre-existing ventricular dysfunction
- Abnormal liver function tests
- Acute hepatic injury (rare) 1, 7
Clinical Pearls
- Always ensure the patient is hemodynamically stable before administering diltiazem
- Confirm the rhythm is SVT and not ventricular tachycardia or pre-excited atrial fibrillation
- Have resuscitation equipment readily available
- Monitor blood pressure and heart rate continuously during administration
- The median time to tachycardia termination is approximately 2 minutes after completion of the diltiazem infusion 5
- In elderly patients, careful monitoring is essential as they may be more susceptible to hypotension and bradycardia 7
For patients who do not respond to diltiazem or have contraindications to its use, alternative options include adenosine, beta-blockers, or synchronized cardioversion depending on clinical circumstances 1, 8.