What is the step‑by‑step algorithm for acute management of supraventricular tachycardia, including assessment of hemodynamic stability, vagal maneuvers, adenosine dosing, calcium‑channel blocker or beta‑blocker therapy, and synchronized cardioversion?

Supraventricular Tachycardia: Acute Management Algorithm

Step 1: Assess Hemodynamic Stability Immediately

If the patient shows hypotension, altered mental status, signs of shock, chest pain, or acute heart failure, proceed directly to synchronized cardioversion—this is the definitive treatment for hemodynamically unstable SVT. 1

• Synchronized cardioversion successfully restores sinus rhythm in essentially all hemodynamically unstable patients 2
• Initial energy: 50-100J for SVT 2
• Do not delay for pharmacologic therapy in unstable patients 1

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Step 2: For Hemodynamically Stable Patients—Vagal Maneuvers First

Vagal maneuvers are the recommended first-line intervention and should be performed immediately before any pharmacologic therapy. 1

Technique specifics:

• Modified Valsalva maneuver: Patient bears down against closed glottis for 10-30 seconds (equivalent to 30-40 mm Hg intrathoracic pressure) in supine position 1
• Carotid sinus massage: Apply steady pressure over carotid sinus for 5-10 seconds after confirming absence of bruit 1
• Ice-water facial immersion: Apply ice-cold wet towel to face 1
• Overall success rate: approximately 27.7% 1, 2

Critical pitfall: Never apply pressure to the eyeball—this is dangerous and abandoned 1

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Step 3: Adenosine Administration (If Vagal Maneuvers Fail)

Adenosine is the recommended pharmacologic agent for acute SVT termination, with 90-95% success rate for AVNRT and 78-96% for AVRT. 1, 3, 2

Dosing protocol:

• Initial dose: 6 mg IV push (not 12 mg) via large proximal vein 3
• Follow immediately with 20 mL saline flush 3
• If no conversion within 1-2 minutes: 12 mg IV push 3
• May repeat 12 mg dose once more if needed 3

Dose modifications:

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, transplanted hearts, or central venous access 3
• Increase dose for patients with significant theophylline, caffeine, or theobromine levels 3

Contraindications:

• Absolute contraindication: Asthma (risk of severe bronchospasm) 3, 2
• AV block (2nd or 3rd degree), sick sinus syndrome 3

Expected side effects (transient, <60 seconds):

• Flushing, dyspnea, chest discomfort 3
• May precipitate atrial fibrillation 2

Critical safety measure:

• Have defibrillator available when administering adenosine if Wolff-Parkinson-White syndrome is a consideration, as adenosine may initiate AF with rapid ventricular rates 3

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Step 4: Alternative Pharmacologic Agents (If Adenosine Fails or Contraindicated)

For hemodynamically stable patients when adenosine fails or is contraindicated (e.g., asthma), use IV calcium channel blockers or beta-blockers. 1

Calcium channel blockers (preferred alternative):

• IV diltiazem 15-20 mg over 2 minutes (64-98% conversion rate) 2, 4
• IV verapamil 2.5-5 mg over 2 minutes 2, 4
• Diltiazem and verapamil are particularly effective for AVNRT 1

Beta-blockers:

• IV esmolol is especially useful for short-term control of SVT, particularly with concurrent hypertension 1
• IV metoprolol is an alternative 1

Critical warnings:

• Do NOT give verapamil or diltiazem if:
  • Ventricular tachycardia cannot be excluded 1
  • Pre-excited atrial fibrillation (Wolff-Parkinson-White) is present—may cause ventricular fibrillation 1, 2
  • Suspected systolic heart failure 1
• Administer slowly (over 20 minutes if possible) to minimize hypotension risk 4

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Step 5: Synchronized Cardioversion (If Pharmacologic Therapy Fails)

For hemodynamically stable patients when pharmacologic therapy is ineffective or contraindicated, proceed to elective synchronized cardioversion. 1

• Highly effective in terminating SVT (AVRT and AVNRT) 1
• Success rate: essentially 100% 2
• Initial energy: 50-100J 2

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Step 6: Post-Conversion Management

Monitor continuously for recurrence immediately after conversion—this is critical as recurrence commonly occurs within seconds to minutes. 3

If recurrence occurs:

• Treat with adenosine again, OR 3
• Consider longer-acting AV nodal blocking agent (diltiazem or beta-blocker) 3

If adenosine unmasks another SVT mechanism:

• Consider treatment with longer-acting AV nodal blocking agent 3

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Special Populations

Pregnancy:

• Vagal maneuvers first-line 1
• Adenosine is safe and effective during pregnancy 3
• Electrical cardioversion if hemodynamically unstable 1

Adult Congenital Heart Disease (ACHD):

• Acute antithrombotic therapy recommended for AT or atrial flutter (align with AF guidelines) 1
• IV adenosine recommended 1
• IV diltiazem or esmolol with caution (observe for hypotension) 1
• Do NOT give flecainide if significant ventricular dysfunction present 1

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Critical Diagnostic Consideration During Treatment

Always obtain 12-lead ECG during tachycardia before treatment to differentiate SVT mechanisms and exclude ventricular tachycardia or pre-excited atrial fibrillation. 2

• Irregular rhythm suggests AF, multifocal atrial tachycardia, or premature depolarizations—NOT typical AVNRT/AVRT 2
• QRS duration >120 ms requires distinguishing VT from SVT with aberrancy 2
• Adenosine has diagnostic utility: unmasks atrial flutter or atrial tachycardia 1, 3