What is the recommended acute management algorithm for a patient presenting with supraventricular tachycardia, including assessment of hemodynamic stability and treatment steps?

Acute Management of Supraventricular Tachycardia

For hemodynamically unstable SVT (systolic BP <90 mmHg, altered mental status, shock, ischemic chest pain, or acute heart failure), proceed immediately to synchronized cardioversion at 50–100 J without attempting vagal maneuvers or medications—this achieves near-100% termination. 1

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Step 1: Assess Hemodynamic Stability Within 60 Seconds

Unstable indicators:

• Systolic blood pressure <90 mmHg 1
• Altered mental status 1
• Signs of shock 1
• Ischemic chest pain 1
• Acute heart failure or pulmonary edema 1

If any of these are present: perform synchronized cardioversion immediately (50–100 J) after procedural sedation; do not delay for vagal maneuvers or drugs. 1 Have defibrillation equipment and resuscitation drugs at bedside. 1

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Step 2: Hemodynamically Stable Patients—Modified Valsalva Maneuver (First-Line)

Technique:

• Position patient supine 2
• Instruct patient to bear down against a closed glottis for 10–30 seconds, generating intrathoracic pressure ≥30–40 mmHg 1, 2
• Success rate: 43% (2.8–3.8× more effective than standard Valsalva) 1, 2

Alternative vagal maneuvers (if modified Valsalva fails):

• Carotid sinus massage: apply steady pressure for 5–10 seconds after confirming absence of carotid bruit by auscultation 1, 2
• Ice-cold wet towel applied to face 1
• Overall success across all vagal techniques: ~27.7% 1

Critical safety warning: Never apply pressure to the eyeball. 3, 1

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Step 3: Adenosine (First-Line Pharmacologic Agent)

If vagal maneuvers fail, adenosine is the drug of choice, achieving 90–95% conversion for AVNRT and 78–96% for AVRT. 3, 1

Dosing Protocol:

• Initial dose: 6 mg rapid IV push (over 1–2 seconds) via large proximal vein (antecubital preferred), followed immediately by 20 mL saline flush 3, 1
• If no conversion within 1–2 minutes: give 12 mg rapid IV push with saline flush 3, 1
• If still no conversion: repeat 12 mg once more 3, 1
• Maximum cumulative dose: 30 mg (6 + 12 + 12 mg) 3
• Average time to conversion: ~30 seconds after effective dose 3

Dose Adjustments:

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, cardiac transplant recipients, or when given via central venous access 3, 1
• Increase dose if patient has high theophylline, caffeine, or theobromine levels 3, 1

Absolute Contraindications:

• Asthma or active bronchospasm (risk of severe bronchospasm) 3, 1
• Second- or third-degree AV block or sick sinus syndrome without pacemaker 3, 1
• Pre-excited atrial fibrillation (Wolff-Parkinson-White with AF) 3, 1

Common Transient Side Effects (<60 seconds):

• Flushing, dyspnea, chest discomfort (occur in ~30% of patients) 3, 1

Safety Requirement:

• Defibrillator must be immediately available because adenosine can precipitate rapid atrial fibrillation, especially in patients with possible WPW syndrome 3, 1

Diagnostic Role:

• If adenosine fails to convert but produces transient AV block that unmasks atrial flutter or atrial tachycardia, shift to rate control with a longer-acting AV-nodal blocker rather than attempting further rhythm conversion 3, 1

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Step 4: Second-Line Pharmacologic Therapy (If Adenosine Fails or Is Contraindicated)

IV diltiazem is the preferred alternative, achieving 64–98% conversion. 3, 1

Calcium-Channel Blockers:

• Diltiazem: 15–20 mg (≈0.25 mg/kg) IV over 2 minutes 3, 1
• Verapamil: 2.5–5 mg IV over 2 minutes (conversion within 3–5 minutes) 3, 1

Beta-Blockers (Alternative):

• Metoprolol: 2.5–5 mg IV every 2–5 minutes, maximum 15 mg over 10–15 minutes 3, 1
• Esmolol: useful for short-term control, especially with concurrent hypertension 3

Absolute Contraindications for Calcium-Channel Blockers:

• Wide-complex tachycardia where ventricular tachycardia cannot be excluded (risk of hemodynamic collapse) 3, 1
• Pre-excited atrial fibrillation (WPW with AF)—can trigger ventricular fibrillation 3, 1
• Suspected systolic heart failure or severe left-ventricular dysfunction (negative inotropic effects) 3, 1
• Hemodynamic instability 3, 1

Critical Safety Warning:

• Never combine IV calcium-channel blockers with IV beta-blockers due to synergistic hypotensive and bradycardic effects 1

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Step 5: Synchronized Cardioversion (Rescue for Drug-Refractory or Contraindicated Cases)

If pharmacologic therapy fails or is contraindicated in stable patients, perform elective synchronized cardioversion starting at 50–100 J—this achieves near-100% termination of AVRT/AVNRT. 3, 1

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Step 6: Post-Conversion Management

Continuous cardiac monitoring is essential immediately after conversion:

• Watch for premature atrial or ventricular complexes that can trigger recurrent SVT within seconds to minutes 3, 1
• If immediate recurrence occurs: administer a longer-acting AV-nodal blocker (diltiazem or beta-blocker) 3, 1
• Consider prophylactic antiarrhythmic therapy in patients with frequent premature complexes post-conversion 3, 1

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Special Populations

Pregnancy:

• Vagal maneuvers remain first-line 1, 2
• Adenosine is safe and the first-line pharmacologic agent during pregnancy 3, 1
• Synchronized cardioversion is safe at all gestational stages when drugs fail; place pads away from the uterus and perform fetal monitoring if feasible 1, 2

Adult Congenital Heart Disease (ACHD):

• IV adenosine is appropriate for SVT termination 3, 1
• IV diltiazem or esmolol may be used cautiously with close monitoring for hypotension 3, 1
• Avoid flecainide in patients with significant ventricular dysfunction 3, 1
• Synchronized cardioversion is recommended for hemodynamically unstable ACHD patients 1

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Diagnostic Considerations

Obtain a 12-lead ECG during tachycardia to:

• Differentiate SVT mechanisms 3, 1
• Exclude ventricular tachycardia 3, 1
• Exclude pre-excited atrial fibrillation 3, 1
• Guide long-term management decisions 1

If diagnosis remains uncertain after acute management, refer to electrophysiology for invasive study and potential catheter ablation. 1

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Long-Term Management After Acute Episode

Catheter ablation is the first-line definitive therapy for symptomatic recurrent SVT, with single-procedure success rates of 94.3–98.5%. 1, 4

Oral Pharmacologic Options (for patients declining or not candidates for ablation):

• First-line: oral beta-blockers, diltiazem, or verapamil (preferred in patients without ventricular pre-excitation) 1
• Second-line: flecainide or propafenone (only in patients without structural heart disease or coronary artery disease) 1
• Third-line: sotalol or dofetilide (when first-line agents fail) 1

Patient Education:

• Teach vagal maneuvers (modified Valsalva, carotid massage, facial cooling) for self-termination of future episodes 3, 1
• Consider "pill-in-the-pocket" therapy as a personalized self-directed option 3, 1