When is medication indicated for a patient with Supraventricular Tachycardia (SVT)?

When to Medicate for Supraventricular Tachycardia

Medication is indicated immediately for hemodynamically stable SVT after vagal maneuvers fail, starting with adenosine 6 mg IV push, or immediately for hemodynamically unstable SVT (though synchronized cardioversion is preferred unless the rhythm is regular narrow-complex, in which case adenosine can be tried first). 1, 2

Acute Treatment Algorithm

Step 1: Assess Hemodynamic Stability

Hemodynamically Unstable SVT (hypotension, altered mental status, signs of shock, chest pain, or acute heart failure):

• Proceed directly to synchronized cardioversion as the treatment of choice 1, 2
• However, adenosine may still be considered first if the tachycardia is regular with narrow QRS complex 1, 3
• Do not delay cardioversion to attempt medications if the patient is deteriorating 1

Hemodynamically Stable SVT:

• Attempt vagal maneuvers first (modified Valsalva maneuver has 43% success rate) 4, 5
• If vagal maneuvers fail, proceed immediately to medication 1, 2

Step 2: First-Line Medication - Adenosine

Adenosine is the first-line medication for hemodynamically stable regular SVT 1, 2, 3:

• Initial dose: 6 mg rapid IV bolus over 1-2 seconds through a large peripheral vein, followed immediately by 20 mL saline flush 2, 3
• If no conversion within 1-2 minutes: 12 mg rapid IV bolus with same technique 2, 3
• If still no conversion: repeat 12 mg one more time 3
• Success rate: 90-95% for AVNRT and 78-96% for AVRT 2, 3

Critical contraindications to adenosine 3, 6:

• Asthma or bronchospastic lung disease (absolute contraindication due to severe bronchospasm risk) 3, 6
• Second- or third-degree AV block without pacemaker 6
• Sick sinus syndrome without pacemaker 6

Dose modifications for adenosine 3:

• Reduce to 3 mg if patient is taking dipyridamole or carbamazepine, has transplanted heart, or receiving via central line 3
• Increase dose if patient has significant theophylline, caffeine, or theobromine levels 3

Step 3: Second-Line Medications

If adenosine fails or is contraindicated, use calcium channel blockers or beta-blockers 1, 2:

Diltiazem (64-98% conversion rate) 1, 2:

• 0.25 mg/kg (typically 15-20 mg) IV bolus over 2 minutes 2
• Followed by infusion at 5-10 mg/hour if needed 2

Verapamil (64-98% conversion rate) 1, 2:

• 5-10 mg (0.075-0.15 mg/kg) IV bolus over 2 minutes 2
• Additional 10 mg possible after 30 minutes if needed 2
• Then infusion at 0.005 mg/kg/min 2

Metoprolol 2:

• 2.5-5 mg IV bolus over 2 minutes 2
• Can repeat every 10 minutes up to 3 doses 2

Esmolol 2:

• 500 mcg/kg IV bolus over 1 minute 2
• Followed by infusion at 50-300 mcg/kg/min 2

Step 4: Synchronized Cardioversion

Cardioversion is indicated when 1, 2:

• Pharmacological therapy fails in hemodynamically stable patients 1, 2
• Pharmacological therapy is contraindicated 1, 2
• Initial energy: 50-100 J for SVT, with stepwise increases if unsuccessful 2
• Success rate: essentially 100% when appropriately indicated 2

Critical Pitfalls to Avoid

Never use AV nodal blockers (adenosine, calcium channel blockers, beta-blockers) in pre-excited atrial fibrillation or flutter 2:

• These can accelerate ventricular rate and cause hemodynamic collapse or ventricular fibrillation 1, 2
• Check for pre-excitation pattern (delta waves) on baseline ECG 4

Avoid calcium channel blockers in 1, 2, 7:

• Suspected systolic heart failure (ejection fraction <30%) 1, 7
• Severe left ventricular dysfunction 7
• Patients already on beta-blockers (risk of severe bradycardia or heart failure) 7

Confirm narrow-complex SVT before administering AV nodal blocking agents 2:

• Misdiagnosing ventricular tachycardia as SVT and giving calcium channel blockers can be fatal 2

Long-Term Medication Management

After successful acute conversion, medication for ongoing management is indicated for 1, 4:

Frequent episodes (>2 per year) 4:

• Initiate oral beta-blockers, diltiazem, or verapamil as first-line suppressive therapy 1, 4
• These medications have Class I recommendation for ongoing management 1, 4

Infrequent episodes (1-2 per year) 4:

• Teach vagal maneuvers as primary management 4
• Consider "pill-in-the-pocket" approach with oral calcium channel blockers or beta-blockers for patient self-administration 3

However, catheter ablation should be discussed as first-line definitive therapy 4:

• Success rates of 94-98% 4, 5
• More cost-effective than long-term medication 4
• Preferred over chronic pharmacotherapy for recurrent symptomatic SVT 4

Special Populations

Pregnancy: Adenosine is safe and effective 3

Asthma/COPD: Use IV diltiazem or verapamil instead of adenosine; use beta-blockers with extreme caution 3

Heart transplant patients: Reduce adenosine dose to 3 mg initially 3