Role of Cardizem (Diltiazem) in the Treatment of Supraventricular Tachycardia (SVT)
Intravenous diltiazem is highly effective for acute treatment of hemodynamically stable SVT, with conversion success rates of 64-98% of patients, and should be considered a first-line pharmacological treatment option after vagal maneuvers and adenosine. 1
Mechanism of Action
- Diltiazem inhibits calcium ion influx during cardiac membrane depolarization, specifically slowing AV nodal conduction time and prolonging AV nodal refractoriness 2
- It exhibits frequency-dependent effects on AV nodal conduction, selectively reducing heart rate during tachycardias involving the AV node 2
- Diltiazem converts paroxysmal SVT to normal sinus rhythm by interrupting the reentry circuit in AV nodal reentrant tachycardias and reciprocating tachycardias 2
Acute Management of SVT
Treatment Algorithm
First-line approaches:
Second-line pharmacological options:
When pharmacological therapy fails:
- Synchronized cardioversion (Class I recommendation) 1
Efficacy of IV Diltiazem
- Conversion rates with diltiazem doses of 0.15-0.45 mg/kg are superior to placebo (82-100% vs 25%) 4
- Median time to conversion is approximately 2-3 minutes after diltiazem administration 4, 5
- Diltiazem can effectively rescue cases not responsive to adenosine (35% of adenosine failures) 6
Important Considerations
- Ensure tachycardia is not ventricular tachycardia or pre-excited atrial fibrillation before administering diltiazem, as these patients may become hemodynamically unstable 1
- Diltiazem should be avoided in patients with suspected systolic heart failure 1
- A slow infusion of diltiazem up to 20 minutes may reduce the risk of hypotension 1
Long-term Management of SVT
Oral diltiazem is a Class I recommendation (highest level) for ongoing management of symptomatic SVT in patients without ventricular pre-excitation 1
Other Class I options include:
For patients who cannot undergo or prefer not to have catheter ablation, oral diltiazem provides effective long-term control of SVT symptoms 1, 7
Specific SVT Types and Diltiazem Efficacy
- AV Nodal Reentrant Tachycardia (AVNRT): Diltiazem has shown 100% conversion rates in clinical studies 5
- AV Reciprocating Tachycardia: Diltiazem demonstrates 81% conversion rates 5
- Atrial Fibrillation/Flutter: Diltiazem effectively controls ventricular rate and occasionally converts to sinus rhythm 8
Safety Profile
- Most common adverse effect is hypotension (approximately 11% of patients), typically responding well to fluid administration 4, 8
- Contraindicated in patients with:
- Severe hypotension
- Sick sinus syndrome without pacemaker
- Second or third-degree AV block without pacemaker
- Cardiogenic shock 2
Diltiazem's excellent efficacy and relatively favorable safety profile make it a valuable option in both acute and chronic management of SVT when used appropriately in hemodynamically stable patients.