What is the recommended initial treatment for Supraventricular Tachycardia (SVT)?

Initial Treatment for Supraventricular Tachycardia

For hemodynamically stable SVT, perform vagal maneuvers first, followed immediately by adenosine 6 mg IV push if vagal maneuvers fail, then escalate to 12 mg adenosine if the first dose is ineffective within 1-2 minutes. 1, 2

Immediate Assessment and Stabilization

• If the patient is hemodynamically unstable (hypotension, altered consciousness, chest pain, severe dyspnea), proceed directly to synchronized cardioversion rather than attempting vagal maneuvers or medications 1, 2
• Confirm the rhythm is truly SVT and not ventricular tachycardia before administering any AV nodal blocking agents, as misdiagnosis can be fatal 2
• Look for signs of pre-excitation (delta waves, short PR interval) on prior ECGs, as this fundamentally changes your treatment approach 3, 2

First-Line: Vagal Maneuvers (Hemodynamically Stable Patients)

Vagal maneuvers terminate up to 25-27.7% of paroxysmal SVT episodes and should always be attempted first. 1, 2

Recommended Techniques (in order of preference):

• Modified Valsalva maneuver: Have the patient lie supine and forcefully exhale against a closed airway for 10-30 seconds, then immediately raise their legs to 45 degrees for 15 seconds after strain release 2, 4
• Ice-cold wet towel to face: Apply directly to the face to trigger the diving reflex 3, 2
• Carotid sinus massage: Apply steady pressure over the carotid sinus for 5-10 seconds, but ONLY after confirming absence of carotid bruits 2
• Never apply pressure to the eyeball - this dangerous practice has been abandoned 2

Critical Technique Points:

• Perform all vagal maneuvers with the patient in the supine position for maximum effectiveness 2
• If one technique fails, switch to another technique as this increases success rates to approximately 27.7% 2

Second-Line: Adenosine (If Vagal Maneuvers Fail)

Adenosine has a 91-95% effectiveness rate for terminating paroxysmal SVT and is the preferred first-line medication. 1, 2

Standard Dosing Protocol:

• Initial dose: 6 mg rapid IV push through a large antecubital vein, followed immediately by a 20 mL saline flush 1
• Second dose: 12 mg rapid IV push if no conversion within 1-2 minutes, using the same technique 1
• Have a defibrillator immediately available, as adenosine can precipitate atrial fibrillation with rapid ventricular rates in patients with Wolff-Parkinson-White syndrome 1

Dose Modifications:

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if administering via central venous access 1
• Increase doses may be required in patients with significant theophylline, caffeine, or theobromine levels 1
• Contraindicated in patients with asthma 1
• Safe and effective in pregnancy 1

Expected Side Effects:

• Flushing, dyspnea, and chest discomfort are common but transient 1

Third-Line: Calcium Channel Blockers or Beta-Blockers

If adenosine fails, intravenous diltiazem or verapamil are highly effective for converting AVNRT to sinus rhythm (Class IIa recommendation). 2

• Beta-blockers have a Class IIa recommendation but are less effective than calcium channel blockers 2
• These agents work more slowly than adenosine but have fewer severe side effects than verapamil in randomized trials 1

Critical Safety Pitfalls to Avoid

Absolute Contraindications for AV Nodal Blockers:

• Never use verapamil, diltiazem, or beta-blockers in wide-complex tachycardia of uncertain etiology - this can cause hemodynamic collapse if the rhythm is ventricular tachycardia or pre-excited atrial fibrillation 3, 2
• Never use AV nodal blocking agents in patients with manifest accessory pathways (WPW) - they can enhance accessory pathway conduction during atrial fibrillation and precipitate ventricular fibrillation 3, 2
• Avoid calcium channel blockers and beta-blockers in patients with systolic heart failure 3, 2

Special Population: Pre-Excited Atrial Fibrillation

• If the patient has pre-excited AF (irregular wide-complex tachycardia with delta waves), use procainamide or ibutilide instead of AV nodal blockers, or proceed directly to synchronized cardioversion 3, 2

When to Escalate to Cardioversion

• Hemodynamic instability at any point 1, 2
• Failure of pharmacological therapy 2
• For automatic tachycardias (ectopic atrial tachycardia, multifocal atrial tachycardia, junctional tachycardia), cardioversion is not effective - these require rate control with AV nodal blocking agents 1

Cardioversion Energy Levels:

• Initial energy for SVT: 50-100 J biphasic 1
• Increase dose stepwise if initial shock fails 1
• Monophasic waveforms should begin at 200 J 1

Patient Instructions for Future Episodes

• Teach patients to apply an ice-cold wet towel to their face immediately when symptoms begin 3
• Instruct patients to seek emergency care if vagal maneuvers fail to terminate the episode within 15-20 minutes 3
• Patients should go to the emergency department immediately if they develop syncope, hypotension, altered consciousness, chest pain, or severe dyspnea during an episode 3