What is the initial treatment for a patient presenting with Supraventricular Tachycardia (SVT)?

Initial Treatment for Supraventricular Tachycardia (SVT)

Begin with vagal maneuvers immediately in all hemodynamically stable patients, followed by intravenous adenosine if vagal maneuvers fail, but proceed directly to synchronized cardioversion in any hemodynamically unstable patient. 1, 2, 3

Step 1: Assess Hemodynamic Stability

The first critical decision is determining whether the patient is hemodynamically stable or unstable. 3

• Hemodynamically unstable patients exhibit hypotension, altered mental status, signs of shock, chest pain, or acute heart failure 3
• If any of these signs are present, proceed immediately to synchronized cardioversion at 50-100J without attempting vagal maneuvers or medications 2, 3
• Do not waste time with vagal maneuvers or pharmacologic therapy in unstable patients—every second counts 3

Step 2: Treatment for Hemodynamically Stable Patients

First-Line: Vagal Maneuvers (Class I, Level B Evidence)

Vagal maneuvers should be performed immediately as the first-line intervention in all stable patients with regular SVT. 1, 2

The modified Valsalva maneuver is the most effective vagal technique, with significantly higher success rates than standard carotid sinus massage. 2, 4

• Modified Valsalva technique: Patient bears down against a closed glottis for 10-30 seconds (equivalent to 30-40 mm Hg intrathoracic pressure) while supine, then immediately lies flat with legs elevated 1, 2
• The modified Valsalva is 2.8-3.8 times more effective than standard Valsalva and achieves 43% conversion rate versus 27.7% for carotid sinus massage 3, 4
• Alternative vagal maneuvers include carotid sinus massage (after confirming absence of bruit, apply steady pressure for 5-10 seconds) or applying ice-cold wet towel to the face 1
• Critical safety note: Avoid applying pressure to the eyeball—this practice is potentially dangerous and has been abandoned 1

Second-Line: Intravenous Adenosine (Class I, Level B Evidence)

If vagal maneuvers fail, adenosine is the next intervention with 90-95% effectiveness for terminating SVT. 1, 2, 3

Adenosine dosing and administration:

• Standard dose: 6 mg rapid IV bolus via large peripheral vein, followed by 20 mL saline flush 3
• If 6 mg fails, give 12 mg, then another 12 mg if needed 5
• Dose adjustments required: Reduce to 3 mg for patients taking dipyridamole, carbamazepine, or with transplanted heart 2
• Larger doses may be needed with theophylline, caffeine, or theobromine 2
• Electrical cardioversion equipment must be immediately available when administering adenosine, as it may precipitate atrial fibrillation that can conduct rapidly and cause ventricular fibrillation 1, 2, 6

Contraindications to adenosine:

• Absolute contraindication: Asthma or bronchospastic lung disease—adenosine can cause severe, life-threatening bronchoconstriction 2, 6
• Second- or third-degree AV block (unless patient has functioning pacemaker) 6
• Sinus node disease or symptomatic bradycardia (unless patient has functioning pacemaker) 6
• Known hypersensitivity to adenosine 6

Third-Line: Alternative AV Nodal Blocking Agents (Class IIa, Level B Evidence)

If adenosine fails or is contraindicated, intravenous diltiazem, verapamil, or beta blockers can be effective for hemodynamically stable SVT. 1

• These agents have 80-98% success rates for SVT termination 1
• Critical safety warning: Never use verapamil or diltiazem in patients with wide-complex tachycardia (QRS ≥120 ms) or known accessory pathways, as this can precipitate ventricular fibrillation 1, 2
• Avoid verapamil and diltiazem in patients with systolic heart failure due to risk of hemodynamic collapse 2

Fourth-Line: Synchronized Cardioversion for Stable Patients

Synchronized cardioversion is recommended when pharmacological therapy is ineffective or contraindicated in hemodynamically stable patients. 1, 2

• Perform after adequate sedation or anesthesia in stable patients 1, 2
• Start with 50-100J for SVT 2, 3
• Cardioversion is highly effective and avoids complications associated with antiarrhythmic drug therapy 1

Critical Pitfalls and Safety Warnings

Wide-Complex Tachycardia

If the QRS duration is >120 ms, it is crucial to distinguish ventricular tachycardia from SVT with aberrant conduction. 1

• Treat wide-complex tachycardia as ventricular tachycardia until proven otherwise—giving AV nodal blockers to VT can be catastrophic 3
• Obtain a 12-lead ECG immediately to determine if QRS is narrow (<120 ms) or wide (≥120 ms) 3

Pre-Excited Atrial Fibrillation (Irregular Wide-Complex)

Never give adenosine, verapamil, diltiazem, or beta blockers to patients with pre-excited atrial fibrillation, as these can accelerate ventricular rate and cause ventricular fibrillation. 3

• For unstable patients: immediate synchronized cardioversion 1, 3
• For stable patients: IV ibutilide or procainamide 1, 3

Post-Conversion Management

Patients often have atrial or ventricular premature complexes immediately after conversion that may reinitiate tachycardia. 1

• An antiarrhythmic drug may be required to prevent acute reinitiation 1, 3
• Arrange cardiology follow-up for consideration of catheter ablation, which has 94.3-98.5% single-procedure success rate 3, 5

Automatic Tachycardias

Automatic tachycardias (ectopic atrial tachycardia, multifocal atrial tachycardia, junctional tachycardia) are not responsive to cardioversion and require rate control with AV nodal blocking agents instead. 2