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

Initial Treatment for Supraventricular Tachycardia

Begin with immediate hemodynamic assessment: if the patient is unstable (hypotension, altered consciousness, chest pain, severe dyspnea), proceed directly to synchronized cardioversion at 50-100 J biphasic energy; if stable, start with the modified Valsalva maneuver, followed by adenosine 6 mg rapid IV push if vagal maneuvers fail. 1

Hemodynamic Stability Assessment

First, determine if the patient is hemodynamically unstable by looking for:

• Hypotension 2
• Altered consciousness 2
• Chest pain 2
• Severe dyspnea 2
• Syncope 2

If any of these are present, skip all other interventions and perform immediate synchronized cardioversion without attempting vagal maneuvers or medications. 1

Treatment Algorithm for Hemodynamically Stable Patients

Step 1: Modified Valsalva Maneuver (First-Line)

The modified Valsalva maneuver is the most effective vagal technique and should be attempted first in all stable patients. 1

Technique:

• Have the patient bear down against a closed glottis for 10-30 seconds while supine 1
• Immediately after, have them lie flat with legs elevated 1
• This modified approach has significantly higher success rates than standard carotid sinus massage 1

The modified Valsalva maneuver carries Class I, Level B evidence from the ACC/AHA/HRS guidelines. 1 Alternative vagal maneuvers like carotid sinus massage or applying an ice-cold wet towel to the face can be used if the modified Valsalva fails. 2, 1

Step 2: Adenosine (If Vagal Maneuvers Fail)

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

Dosing:

• Standard dose: 6 mg rapid IV push through a large peripheral vein 1
• Follow immediately with a 20 mL saline flush 1
• Have electrical cardioversion equipment immediately available at bedside 1

Critical dosing adjustments:

• Reduce to 3 mg for patients taking dipyridamole, carbamazepine, or with transplanted heart 1
• Larger doses may be needed with theophylline, caffeine, or theobromine 1

Absolute contraindication: Adenosine is contraindicated in asthma patients due to risk of severe bronchoconstriction. 1, 3

Step 3: Synchronized Cardioversion (If Adenosine Fails)

After failed pharmacotherapy in stable patients, proceed to synchronized cardioversion with adequate sedation/anesthesia. 1

Critical Safety Warnings

Never use AV nodal blocking agents (verapamil, diltiazem, 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 2, 1
• Patients with known accessory pathways (WPW syndrome) who develop atrial fibrillation—use procainamide or ibutilide instead, or perform immediate cardioversion 2
• Patients with systolic heart failure 2, 1

Common pitfall: Administering calcium channel blockers or beta-blockers to patients with wide-complex tachycardia can precipitate ventricular fibrillation if an accessory pathway is present. 2

Special Considerations

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

Always have resuscitation equipment available when administering adenosine, as fatal cardiac events including cardiac arrest, ventricular arrhythmias, and myocardial infarction have occurred. 1, 3