What are the recommended doses for acute management of Supraventricular Tachycardia (SVT)?

Recommended Doses for Acute Management of Supraventricular Tachycardia

For acute SVT management, start with adenosine 6 mg IV rapid bolus, followed by up to two doses of 12 mg if needed, with each dose pushed rapidly and followed immediately by a 20 mL normal saline flush. 1

First-Line Pharmacologic Therapy: Adenosine Dosing

Standard Dosing Protocol:

• Initial dose: 6 mg IV rapid bolus over 1-2 seconds 1
• Second dose: 12 mg IV rapid bolus if first dose ineffective after 1-2 minutes 1
• Third dose: 12 mg IV rapid bolus if second dose ineffective 1
• Administration technique: Must be given as rapid IV push followed immediately by 20 mL normal saline flush to ensure drug reaches the heart before metabolism 1, 2

Higher Doses in Refractory Cases:

• Doses up to 24 mg have been safely reported and may be necessary in select patients 1
• In cases of impaired venous return (e.g., right heart failure, pulmonary hypertension), doses up to 36 mg have been used successfully, though this exceeds standard recommendations 3, 4
• Consultation with cardiology is recommended before exceeding 12 mg doses 4

Second-Line IV Medications (When Adenosine Fails or is Contraindicated)

Calcium Channel Blockers:

• Diltiazem or verapamil are reasonable alternatives with 64-98% success rates 1, 5
• Use only in hemodynamically stable patients 1
• Critical caveat: Must exclude ventricular tachycardia or pre-excited atrial fibrillation before administration, as these agents can cause hemodynamic collapse or ventricular fibrillation in these rhythms 1, 5

Beta Blockers:

• Esmolol: Loading dose of 500 mcg/kg over 1 minute, followed by maintenance infusion of 50 mcg/kg/min for 4 minutes, titrated up to maximum 200 mcg/kg/min 6
• Metoprolol or propranolol IV are reasonable alternatives 1
• Beta blockers have excellent safety profile but may be less effective than calcium channel blockers for acute termination 1

Special Population: Pregnant Patients

Adenosine dosing remains the same in pregnancy:

• 6 mg initial dose, then 12 mg × 2 if needed 1
• Adenosine is safe due to extremely short half-life (unlikely to reach fetal circulation) 1
• Maternal side effects (chest discomfort, flushing) are transient 1

Alternative agents if adenosine fails:

• IV metoprolol or propranolol are reasonable second-line options 1
• IV verapamil may be considered but carries higher risk of maternal hypotension compared to adenosine 1

Synchronized Cardioversion (Non-Pharmacologic)

Indications:

• Hemodynamically unstable patients: immediate cardioversion 1
• Hemodynamically stable patients when pharmacologic therapy fails or is contraindicated 1
• Energy dosing follows standard protocols (not specified in guidelines but typically start at 50-100 J synchronized) 1

Critical Pitfalls to Avoid

• Inadequate adenosine administration: The drug must be pushed rapidly as a bolus with immediate saline flush; slow administration results in complete metabolism before reaching the heart 2
• Wrong rhythm identification: Never give calcium channel blockers or beta blockers if ventricular tachycardia or pre-excited atrial fibrillation is possible 1, 5
• Peripheral IV access: Adenosine given through peripheral IV may require higher doses due to longer transit time; central access is preferable if available 3
• Caffeine/theophylline use: These adenosine antagonists may require higher doses for effectiveness 2