What is the initial management of a patient with supraventricular tachycardia, including approach for hemodynamically stable versus unstable presentations?

Management of Supraventricular Tachycardia

For hemodynamically unstable SVT (hypotension, altered mental status, shock, chest pain, or acute heart failure), perform immediate synchronized cardioversion after sedation without attempting vagal maneuvers or medications—this restores sinus rhythm in nearly 100% of cases. 1, 2

Immediate Hemodynamic Assessment

Determine stability by checking for:

• Hypotension (systolic BP <90 mmHg)
• Altered mental status or confusion
• Signs of shock (cold extremities, poor perfusion)
• Ischemic chest pain
• Acute heart failure (pulmonary edema, severe dyspnea) 1, 2

If any of these are present, proceed directly to cardioversion—do not waste time with vagal maneuvers or drugs. 1, 2

Management Algorithm for Hemodynamically Stable SVT

Step 1: Vagal Maneuvers (First-Line)

Begin with vagal maneuvers before any medication—they terminate SVT in approximately 27-43% of cases. 1, 2

Perform in this order:

• Modified Valsalva maneuver: Patient supine, bearing down against closed glottis for 10-30 seconds (generating 30-40 mmHg intrathoracic pressure)—most effective single technique with 43% success rate 1, 2
• Carotid sinus massage: After confirming absence of bruit by auscultation, apply steady pressure over carotid sinus for 5-10 seconds (avoid in elderly or those with carotid disease) 1, 2
• Ice-water facial immersion: Apply ice-cold wet towel to face to activate diving reflex 1, 2

Critical safety warning: Never apply pressure to the eyeball—this technique is dangerous and has been abandoned. 1, 2

Step 2: Adenosine (First-Line Pharmacologic)

If vagal maneuvers fail, adenosine is the drug of choice—it terminates 90-95% of AVNRT and 78-96% of AVRT episodes. 1, 2, 3

Dosing protocol:

• 6 mg rapid IV push (over 1-2 seconds) through large proximal vein (antecubital preferred), followed immediately by 20 mL saline flush 1, 2
• If no conversion within 1-2 minutes: 12 mg rapid IV push with flush 1, 2
• If still no conversion: second 12 mg dose (maximum cumulative 30 mg) 1, 2

Dose adjustments:

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, cardiac transplant recipients, or when giving via central line 1, 2
• Increase dose in patients with high caffeine, theophylline, or theobromine levels 1, 2

Absolute contraindications:

• Asthma or active bronchospasm—risk of severe bronchospasm 1, 2
• Second- or third-degree AV block or sick sinus syndrome without pacemaker 1, 2

Expected side effects (occur in ~30%, resolve in <60 seconds):

• Flushing (most common)
• Chest discomfort
• Dyspnea 1, 2, 4

Critical preparation: Have defibrillator immediately available—adenosine can precipitate rapid atrial fibrillation, especially in Wolff-Parkinson-White syndrome. 1, 2

Step 3: Calcium-Channel Blockers or Beta-Blockers (Second-Line)

If adenosine fails or is contraindicated (e.g., asthma), use IV calcium-channel blockers—they achieve 64-98% conversion rates. 1, 2

Preferred agent: Diltiazem

• 15-20 mg (0.25 mg/kg) IV over 2 minutes 1, 2
• Slower infusion over 20 minutes reduces hypotension risk 2, 5

Alternative: Verapamil

• 2.5-5 mg IV over 2 minutes, clinical effect within 3-5 minutes 1, 2

Alternative: Beta-blockers (slightly less effective but excellent safety profile)

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

Absolute contraindications for calcium-channel blockers:

• Ventricular tachycardia cannot be excluded—may cause hemodynamic collapse 1, 2, 5
• Pre-excited atrial fibrillation (WPW syndrome)—can precipitate ventricular fibrillation and death 1, 2, 5
• Suspected systolic heart failure—negative inotropic effects 1, 2, 5
• Hemodynamic instability 1, 2

Never combine IV calcium-channel blockers with IV beta-blockers—synergistic hypotension and bradycardia. 2, 5

Step 4: Synchronized Cardioversion (Rescue for Stable Patients)

When all medications fail or are contraindicated, perform elective synchronized cardioversion with appropriate sedation—achieves 80-98% success in stable patients. 1, 2, 5

Post-Conversion Management

Continuous cardiac monitoring is essential immediately after conversion—premature atrial or ventricular complexes commonly trigger recurrent SVT within seconds to minutes. 1, 2

If immediate recurrence occurs:

• Administer a longer-acting AV-nodal blocker (diltiazem or beta-blocker) to prevent reinitiation 1, 2
• Consider antiarrhythmic drug for patients with frequent premature complexes 2

If adenosine revealed atrial flutter or atrial tachycardia (by unmasking atrial activity):

• Treat with longer-acting AV-nodal blocker for rate control rather than attempting rhythm conversion 1, 2

Special Populations

Pregnancy

• Vagal maneuvers remain first-line 1, 2
• Adenosine is safe and effective during pregnancy 1, 2
• Synchronized cardioversion if unstable 2, 6

Adult Congenital Heart Disease

• Adenosine appropriate for SVT termination 2
• IV diltiazem or esmolol may be used cautiously, monitoring for hypotension 2
• Avoid flecainide in significant ventricular dysfunction 2

Critical Pitfalls to Avoid

• Never delay cardioversion in unstable patients to attempt vagal maneuvers or drugs 1, 2, 5
• Never give calcium-channel blockers when VT or pre-excited AF is possible—can cause ventricular fibrillation and death 1, 2, 5
• Never use adenosine in asthma—risk of severe bronchospasm 1, 2
• Never apply eyeball pressure—dangerous and abandoned 1, 2
• Always obtain 12-lead ECG during tachycardia to differentiate SVT from VT and identify pre-excitation 1, 2

Long-Term Management

Catheter ablation should be offered as first-line definitive therapy for all patients with symptomatic recurrent SVT—single-procedure success rates are 94.3-98.5% with low complication rates, providing cure without chronic medication. 2, 5, 3, 7

If ablation declined or unsuitable, pharmacologic options:

• Oral beta-blockers, diltiazem, or verapamil (first-line for prevention) 1, 2, 5
• Flecainide or propafenone (86-93% effective at 12 months) only in patients without structural heart disease, ischemic heart disease, or LV dysfunction—absolutely contraindicated otherwise due to pro-arrhythmic risk 2, 5
• Sotalol when first-line agents fail 2, 5
• Dofetilide when all other options ineffective or contraindicated 2, 5

Patient education: Teach all patients vagal maneuvers (modified Valsalva, carotid massage when appropriate, facial cooling) for self-termination of future episodes—perform supine for maximum effectiveness. 2, 5