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

Initial Treatment for Supraventricular Tachycardia (SVT)

Begin with immediate assessment of hemodynamic stability: if the patient is unstable (hypotension, altered mental status, shock, chest pain, or acute heart failure), proceed directly to synchronized cardioversion at 50-100J without attempting vagal maneuvers or medications; if stable, start with vagal maneuvers followed by adenosine if unsuccessful. 1, 2

Hemodynamically Unstable Patients

Perform immediate synchronized cardioversion without delay. 3, 1, 2

• Do not waste time with vagal maneuvers or pharmacologic therapy in unstable patients—every second counts and cardioversion is the definitive treatment. 2
• Start with 50-100J biphasic energy and increase stepwise if the initial shock fails. 1
• Have defibrillation capability immediately available in case the rhythm degenerates to ventricular fibrillation. 2
• Perform cardioversion after adequate sedation/anesthesia only if the patient is stable enough to tolerate brief delay. 3

Hemodynamically Stable Patients: Step-by-Step Algorithm

Step 1: Vagal Maneuvers (First-Line)

Perform vagal maneuvers immediately as Class I, Level B evidence supports this as first-line treatment. 3, 1

• Modified Valsalva maneuver is the most effective technique with 43% success rate and 2.8-3.8 times more effective than standard Valsalva. 1, 2, 4
• Technique: Patient bears down against closed glottis for 10-30 seconds (equivalent to 30-40 mm Hg intrathoracic pressure) while supine, then immediately lies flat with legs elevated. 3, 1
• Alternative: Carotid sinus massage for 5-10 seconds after confirming absence of bruit by auscultation (apply steady pressure over right or left carotid sinus). 3
• Ice-cold wet towel to face is another option based on diving reflex. 3
• Never apply pressure to the eyeball—this is dangerous and abandoned. 3

Step 2: Adenosine (If Vagal Maneuvers Fail)

Administer adenosine 6 mg rapid IV bolus as Class I, Level B recommendation with 90-95% effectiveness for terminating SVT. 3, 1, 2, 5

• Give as rapid IV push through large peripheral vein followed immediately by 20 mL saline flush. 1
• If unsuccessful, give 12 mg, then another 12 mg if needed. 1
• Critical dosing adjustments: Reduce to 3 mg for patients taking dipyridamole, carbamazepine, or with transplanted heart; larger doses may be needed with theophylline, caffeine, or theobromine. 1
• Have electrical cardioversion equipment immediately available as adenosine may precipitate atrial fibrillation that could conduct rapidly and cause ventricular fibrillation. 3, 1
• Contraindicated in asthma patients due to risk of severe bronchoconstriction. 1
• Expect minor, brief side effects (<1 minute) in approximately 30% of patients. 3
• Adenosine will also unmask atrial flutter or atrial tachycardia by causing transient AV block without terminating the rhythm. 2

Step 3: Alternative Pharmacologic Therapy (If Adenosine Fails or Contraindicated)

Intravenous diltiazem or verapamil are Class IIa, Level B recommendations for hemodynamically stable SVT. 3

• Intravenous beta blockers are also reasonable as Class IIa, Level C recommendation. 3
• These agents have 80-98% success rates for SVT termination. 3

Step 4: Synchronized Cardioversion (If Pharmacologic Therapy Fails)

Perform synchronized cardioversion after adequate sedation/anesthesia when medications are ineffective or contraindicated in stable patients. 3

• This is highly effective and is Class I, Level B recommendation. 3

Critical Safety Warnings and Pitfalls

Wide-Complex Tachycardia Warning

Never give AV nodal blocking agents (verapamil, diltiazem, adenosine, beta blockers) to patients with wide-complex tachycardia (QRS ≥120 ms) of uncertain etiology—treat as ventricular tachycardia until proven otherwise. 1, 2

• Giving verapamil or diltiazem for ventricular tachycardia can lead to hemodynamic collapse. 3
• Obtain 12-lead ECG immediately to determine if QRS is narrow (<120 ms) or wide (≥120 ms). 2

Pre-Excited Atrial Fibrillation Warning

For irregular wide-complex tachycardia (pre-excited AF), never give adenosine, verapamil, diltiazem, or beta blockers—these can accelerate ventricular rate and cause ventricular fibrillation. 3, 2

• Use synchronized cardioversion if unstable, or IV ibutilide/procainamide if stable. 3, 2
• These medications slow conduction over the accessory pathway rather than enhancing it. 3

Heart Failure Warning

Avoid verapamil and diltiazem in patients with systolic heart failure due to risk of hemodynamic collapse. 1

Post-Conversion Management

• Patients often have atrial or ventricular premature complexes immediately after conversion that may reinitiate tachycardia—an antiarrhythmic drug may be required to prevent acute recurrence. 3
• Arrange cardiology follow-up for consideration of catheter ablation, which has 94.3-98.5% single-procedure success rate. 2, 5

Special Consideration: 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. 1