What are the initial medication treatments for a patient experiencing supraventricular tachycardia (SVT)?

Initial Medication Treatment for Supraventricular Tachycardia (SVT)

First-Line Acute Treatment

For hemodynamically stable patients with regular SVT, adenosine is the recommended first-line medication after attempting vagal maneuvers. 1

Adenosine Dosing Protocol

• Initial dose: 6 mg rapid IV bolus administered over 1-2 seconds through a large peripheral vein (antecubital preferred), immediately followed by a 20 mL saline flush 1

• Second dose: 12 mg rapid IV bolus if no conversion within 1-2 minutes, using the same technique 1

• Third dose: 12 mg may be repeated once more if the second dose fails 1

• Success rate: 90-95% for terminating PSVT involving the AV node (AVNRT and orthodromic AVRT) 1

Important Adenosine Considerations

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or when administering via central venous access 1, 2

• Higher doses may be needed in patients with significant theophylline, caffeine, or theobromine levels 1

• Have a defibrillator immediately available as adenosine may precipitate atrial fibrillation with rapid ventricular response in patients with pre-excitation (WPW), potentially leading to ventricular fibrillation 1

• Common transient side effects (lasting <1 minute) include flushing, dyspnea, and chest discomfort in approximately 30% of patients 1

• Contraindicated in asthma patients due to risk of bronchospasm 1

Recent Evidence on Initial Dosing

A 2025 study of 11,245 prehospital patients found that starting with 12 mg adenosine was associated with 65% increased odds of immediate conversion and 28% reduced hospital admission compared to the traditional 6 mg initial dose, with no difference in complications 3. However, current guidelines still recommend the 6 mg-12 mg-12 mg escalation protocol 1.

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

For Hemodynamically Stable Patients

Intravenous calcium channel blockers or beta-blockers are the next appropriate choices for regular SVT without pre-excitation 1:

Calcium Channel Blockers (Class I Recommendation)

• Diltiazem: 0.25 mg/kg IV bolus over 2 minutes, followed by infusion at 5-10 mg/h (up to 15 mg/h) 1

• Verapamil: 5-10 mg (0.075-0.15 mg/kg) IV bolus over 2 minutes, with additional 10 mg possible after 30 minutes if needed, then infusion at 0.005 mg/kg/min 1

• Critical warning: Never use verapamil or diltiazem if ventricular tachycardia or pre-excited atrial fibrillation is suspected, as this may precipitate ventricular fibrillation 1, 4

Beta-Blockers (Class IIa Recommendation)

• Metoprolol: 2.5-5 mg IV bolus over 2 minutes, can repeat every 10 minutes up to 3 doses 1

• Esmolol: 500 mcg/kg IV bolus over 1 minute, followed by infusion at 50-300 mcg/kg/min with repeat boluses between dosing increases 1

• Propranolol: 1 mg IV over 1 minute, can repeat at 2-minute intervals up to 3 doses 1

For Refractory Cases

If initial AV nodal blockers fail, consider combination therapy or alternative agents 4:

• Adding a beta-blocker to verapamil or vice versa may achieve success rates of 80-98% 4

• Intravenous amiodarone may be considered when other therapies are ineffective or contraindicated, though onset is slower than adenosine 1, 4

• Intravenous procainamide is an alternative option for refractory SVT 5

Synchronized Cardioversion

Immediate synchronized cardioversion is indicated in the following scenarios 1:

• Hemodynamically unstable patients at any point (Class I recommendation) 1

• Hemodynamically stable patients when pharmacological therapy fails or is contraindicated (Class I recommendation) 1

• Initial energy: 50-100 J for SVT (often sufficient), with stepwise increases if unsuccessful 1

• Success rate: essentially 100% when appropriately indicated 5

Critical Pitfalls to Avoid

• Do not use AV nodal blockers (verapamil, diltiazem, beta-blockers, digoxin) in pre-excited atrial fibrillation or atrial flutter, as they may accelerate ventricular rate and cause hemodynamic collapse 1, 4

• Avoid calcium channel blockers in patients with suspected systolic heart failure due to risk of worsening heart failure 1, 4

• Confirm narrow-complex SVT before administering AV nodal blocking agents to avoid misdiagnosing ventricular tachycardia 4

• Do not delay cardioversion to obtain a 12-lead ECG if the patient is unstable, though recording one when feasible aids diagnosis 1, 5

• Ensure adequate dosing before declaring treatment failure—a second bolus or higher dose may be effective in resistant cases 1, 4