What is the appropriate acute management for a hemodynamically stable patient with supraventricular tachycardia?

Acute Management of Hemodynamically Stable Supraventricular Tachycardia

For a hemodynamically stable patient with SVT, begin with vagal maneuvers—specifically the modified Valsalva maneuver—followed by adenosine 6 mg IV push if vagal techniques fail, then escalate to 12 mg doses or consider IV diltiazem if adenosine is unsuccessful or contraindicated. 1

Step 1: Confirm Hemodynamic Stability

• Stable patients have systolic BP ≥ 90 mmHg, normal mental status, no chest pain, no signs of shock, and no acute heart failure. 1
• Unstable patients (hypotension, altered mental status, shock, chest pain, acute heart failure) require immediate synchronized cardioversion at 50–100 J without attempting vagal maneuvers or drug therapy. 1, 2

Step 2: Vagal Maneuvers (First-Line for Stable Patients)

• Modified Valsalva maneuver is the most effective vagal technique, terminating SVT in approximately 43% of attempts. 1, 2
• Technique: Patient lies supine and bears down against a closed glottis for 10–30 seconds, generating 30–40 mmHg intrathoracic pressure. 1, 2
• Alternative vagal maneuvers include carotid sinus massage (5–10 seconds after confirming no carotid bruit) or ice-water facial immersion. 1, 2
• Overall vagal maneuver success rate across all techniques is approximately 27–28%. 1
• Critical safety warning: Never apply pressure to the eyeball—this technique is dangerous and abandoned. 1, 2

Step 3: Adenosine (First-Line Pharmacologic Agent)

Dosing Protocol

• Initial dose: 6 mg rapid IV push (over 1–2 seconds) through a large proximal vein (antecubital preferred), followed immediately by a 20 mL saline flush. 1
• Second dose: If no conversion within 1–2 minutes, give 12 mg rapid IV push with saline flush. 1
• Third dose: A second 12 mg dose may be administered if needed (maximum cumulative dose 30 mg). 1

Efficacy

• Adenosine terminates 90–95% of AVNRT and 78–96% of AVRT episodes. 1, 3
• Average time to termination after an effective dose is approximately 30 seconds. 1

Dose Adjustments

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, cardiac transplant recipients, or when administered via central venous access. 1
• Increase dose in patients with significant blood levels of theophylline, caffeine, or theobromine. 1

Absolute Contraindications

• Active asthma or bronchospasm (risk of severe bronchospasm). 1
• Second- or third-degree AV block or sick sinus syndrome without a pacemaker. 1
• Pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White syndrome)—risk of rapid ventricular response and ventricular fibrillation. 1

Common Side Effects

• Flushing, dyspnea, and chest discomfort occur commonly but resolve within <60 seconds. 1, 3
• A defibrillator must be immediately available because adenosine can precipitate rapid atrial fibrillation, especially in patients with WPW. 1

Step 4: Alternative Pharmacologic Options (When Adenosine Fails or Is Contraindicated)

Intravenous Diltiazem (Preferred Alternative)

• Dose: 15–20 mg (≈0.25 mg/kg) IV over 2 minutes; a slower infusion over 20 minutes reduces hypotension risk. 1, 4
• Efficacy: Converts 64–98% of SVT cases. 1
• Preferred for patients with asthma or COPD where adenosine is contraindicated. 1

Intravenous Verapamil (Alternative Calcium-Channel Blocker)

• Dose: 2.5–5 mg IV over 2 minutes; clinical effect typically within 3–5 minutes. 1, 5
• Efficacy: Comparable to diltiazem with 64–98% conversion rates. 1

Intravenous Beta-Blockers (Third-Line)

• Metoprolol: 2.5–5 mg IV every 2–5 minutes (maximum 15 mg over 10–15 minutes). 1
• Esmolol: Useful for short-term rate control, particularly when concurrent hypertension is present. 1
• Use cautiously in severe COPD and never combine IV calcium-channel blockers with IV beta-blockers due to synergistic hypotension and bradycardia. 1

Absolute Contraindications for Calcium-Channel Blockers

• Cannot exclude ventricular tachycardia (may precipitate ventricular fibrillation and death). 1, 4
• Pre-excited atrial fibrillation (WPW syndrome). 1
• Suspected systolic heart failure or severe left-ventricular dysfunction. 1, 4
• Any hemodynamic instability (hypotension, shock). 1

Step 5: Synchronized Cardioversion (Rescue for Stable Patients)

• When all pharmacologic options fail or are contraindicated, elective synchronized cardioversion with appropriate sedation achieves 80–98% success. 1
• This is appropriate even in hemodynamically stable patients when drugs are ineffective. 1

Step 6: Post-Conversion Management

• Continuous cardiac monitoring is essential immediately after conversion because premature atrial or ventricular complexes frequently trigger recurrent SVT within seconds to minutes. 1
• If immediate recurrence occurs, administer a longer-acting AV-nodal blocker (e.g., oral diltiazem or a β-blocker) to prevent re-initiation. 1
• If adenosine reveals atrial flutter or atrial tachycardia (by transient AV block), manage with a longer-acting AV-nodal blocker for rate control rather than attempting rhythm conversion. 1

Special Populations

Pregnancy

• Vagal maneuvers remain first-line. 1, 2
• Adenosine is safe and effective during pregnancy. 1
• If hemodynamically unstable, synchronized cardioversion is indicated. 1

Adult Congenital Heart Disease

• Adenosine is appropriate for SVT termination. 1
• IV diltiazem or esmolol may be used cautiously with close blood-pressure monitoring. 1
• Avoid flecainide when significant ventricular dysfunction is present. 1

Critical Pitfalls to Avoid

• Never delay cardioversion in unstable patients to attempt vagal maneuvers or drug therapy. 1
• Never administer calcium-channel blockers when ventricular tachycardia or pre-excited atrial fibrillation is possible—this may precipitate ventricular fibrillation and death. 1, 4
• Never use adenosine in patients with asthma due to risk of severe bronchospasm. 1
• Never combine IV calcium-channel blockers with IV beta-blockers due to synergistic hypotension and bradycardia. 1
• Always obtain a 12-lead ECG during tachycardia to differentiate SVT from VT and identify pre-excitation. 1
• Never apply pressure to the eyeball as a vagal maneuver. 1, 2