What is the recommended intravenous (IV) treatment and dose for Supraventricular Tachycardia (SVT)?

Intravenous Treatment for Supraventricular Tachycardia (SVT)

The first-line intravenous treatment for SVT is adenosine, administered as a 6 mg rapid IV bolus followed by a 20 mL saline flush, with subsequent doses of 12 mg if needed. 1

Initial Management Algorithm

1. First step: Vagal maneuvers

   • Perform in supine position
   • Valsalva maneuver (bearing down against closed glottis for 10-30 seconds)
   • Carotid sinus massage (after confirming absence of bruits)
   • Success rate approximately 27.7% 1

2. Second step: Adenosine administration

   • Initial dose: 6 mg IV rapid bolus followed by immediate 20 mL saline flush 1
   • Use most proximal IV site possible
   • If no response within 30 seconds, administer 12 mg IV rapid bolus with saline flush
   • May repeat 12 mg dose once more if needed 1, 2
   • Two-syringe technique preferred (one for adenosine, one for flush) 3

3. Third step: Calcium channel blockers or beta blockers

   • If adenosine fails or is contraindicated:
     • Diltiazem: 15-20 mg (0.25 mg/kg) IV over 2 minutes; may repeat with 20-25 mg in 15 minutes if needed 1
     • Verapamil: 2.5-5 mg IV over 2 minutes; may repeat with 5-10 mg every 15-30 minutes to maximum 20-30 mg 1
     • Metoprolol: 5 mg IV over 1-2 minutes; may repeat every 5 minutes to maximum 15 mg 1
     • Esmolol: 500 mcg/kg loading dose over 1 minute, followed by infusion of 50-300 mcg/kg/min 1

4. Fourth step: Synchronized cardioversion

   • For hemodynamically unstable patients or when medications fail 1, 4

Special Considerations

Efficacy

• Adenosine has a high success rate (85-100%) for terminating SVT involving the AV node 5
• Approximately 70% of SVT cases convert with the initial 6 mg dose 6
• Calcium channel blockers (slow infusion) have shown higher conversion rates (98%) compared to adenosine (86.5%) in some studies 7

Administration Pearls

• Use rapid administration for adenosine due to its extremely short half-life (0.6-10 seconds) 5
• Continuous ECG monitoring is essential during administration
• Have a defibrillator immediately available 1

Contraindications

• Adenosine: Second/third-degree AV block, sick sinus syndrome, asthma/bronchospastic disease, heart transplant recipients 1, 2
• Calcium channel blockers: Avoid in pre-excited atrial fibrillation, ventricular tachycardia, significant LV dysfunction, PR interval >0.24 seconds, or second/third-degree AV block 4
• Beta blockers: Avoid in asthma, obstructive airway disease, decompensated heart failure 1

Pregnancy Considerations

• Adenosine is first-line for pregnant patients with SVT 1
• Beta blockers (metoprolol, propranolol) are reasonable when adenosine is ineffective 1
• Verapamil may be considered when adenosine and beta blockers are ineffective or contraindicated 1

Potential Adverse Effects

• Adenosine: Flushing, dyspnea, chest discomfort, transient AV block, brief asystole, bronchospasm 2, 5
• Calcium channel blockers: Hypotension, bradycardia, heart failure exacerbation 1
• Beta blockers: Bradycardia, hypotension, bronchospasm, heart failure exacerbation 1

Remember that adenosine's side effects are typically transient due to its very short half-life, making it generally well-tolerated despite the sometimes alarming but brief symptoms patients may experience during administration.