What is the initial management approach for a patient presenting with supraventricular tachycardia (SVT)?

Management of Supraventricular Tachycardia (SVT)

Begin with vagal maneuvers as first-line treatment, specifically the modified Valsalva maneuver performed supine with legs elevated, followed by adenosine 6 mg rapid IV push if vagal maneuvers fail, and proceed to synchronized cardioversion for hemodynamically unstable patients. 1

Initial Assessment and Hemodynamic Stability

Immediately determine hemodynamic stability by assessing for hypotension, altered mental status, chest pain, or acute heart failure—these patients require immediate synchronized cardioversion rather than sequential pharmacologic attempts. 1

First-Line Treatment: Vagal Maneuvers

Vagal maneuvers are the recommended initial intervention and should be attempted before any pharmacologic therapy in hemodynamically stable patients. 1

Modified Valsalva Maneuver (Preferred Technique)

• The modified Valsalva maneuver achieves 43.7% success rate compared to only 24.2% with standard Valsalva and 9.1% with carotid sinus massage. 2
• Perform with patient supine in Trendelenburg position, having them forcefully expire into a syringe or tubing connected to a pressure gauge for at least 15 seconds at 30-40 mmHg pressure. 1, 2, 3
• After the strain phase, immediately lay the patient flat and elevate their legs—this postural modification significantly improves success rates. 4, 2
• The modified technique increased non-pharmacological reversion from 5.3% to 31.7% in clinical practice. 3

Alternative Vagal Maneuvers

• Carotid sinus massage can be performed after confirming absence of carotid bruits by applying steady pressure over the right or left carotid sinus for 5-10 seconds. 1
• Ice-cold stimulus to the face (diving reflex) using an ice-cold wet towel is effective and can be attempted. 1, 4
• Never apply pressure to the eyeball—this technique is dangerous and has been abandoned. 1

Second-Line Treatment: Adenosine

If vagal maneuvers fail, adenosine is the recommended pharmacologic agent with 90-95% effectiveness for terminating AVNRT and orthodromic AVRT. 1

Adenosine Administration

• Dose: 6 mg rapid IV push through a large peripheral vein, followed immediately by a 20 mL saline flush. 4
• If unsuccessful after 1-2 minutes, give 12 mg rapid IV push, followed by another 12 mg if needed. 1
• Have synchronized cardioversion equipment immediately available because adenosine may precipitate atrial fibrillation that could conduct rapidly, potentially causing ventricular fibrillation in patients with accessory pathways. 1, 4
• Minor side effects (flushing, chest discomfort, dyspnea) occur in approximately 30% of patients but last less than 1 minute. 1

Critical Adenosine Pitfall

Do not use adenosine in pre-excited atrial fibrillation (wide, irregular QRS complexes suggesting Wolff-Parkinson-White syndrome with AF)—this can cause hemodynamic collapse. 1, 4

Third-Line Treatment: AV Nodal Blocking Agents

If adenosine fails or is contraindicated in hemodynamically stable patients, intravenous diltiazem or verapamil are reasonable alternatives with 80-98% success rates. 1

Calcium Channel Blocker Administration

• Intravenous diltiazem or verapamil are particularly effective for AVNRT termination. 1
• Confirm the rhythm is NOT ventricular tachycardia or pre-excited AF before administration—these agents can cause ventricular fibrillation in these scenarios. 1, 4
• Avoid in patients with systolic heart failure or hypotension—these agents can worsen hemodynamic status. 1

Beta-Blocker Alternative

• Intravenous beta-blockers (esmolol, metoprolol) are reasonable but less effective than calcium channel blockers for acute termination. 1
• Beta-blockers have an excellent safety profile and may be preferred in patients with contraindications to calcium channel blockers. 1

Synchronized Cardioversion

Synchronized cardioversion is highly effective and should be performed early in specific clinical scenarios. 1

Immediate Cardioversion Indications

• Hemodynamically unstable patients (hypotension, altered mental status, chest pain, acute heart failure) should receive immediate synchronized cardioversion without waiting for pharmacologic attempts. 1
• Pre-excited atrial fibrillation (wide, irregular complexes in WPW) requires immediate cardioversion due to risk of ventricular fibrillation. 1
• Start with 50-100 joules for SVT and increase as needed. 4

Cardioversion for Stable Patients

• Use synchronized cardioversion in hemodynamically stable patients when pharmacologic therapy fails or is contraindicated. 1
• Adequate sedation or anesthesia should be provided before cardioversion in stable patients. 1

Special Populations and Considerations

Patients with Low Baseline Heart Rate

• Use vagal maneuvers first as they won't worsen bradycardia. 4
• Consider reduced adenosine dosing and careful monitoring when administering any rate-controlling medication. 4
• Move to synchronized cardioversion earlier in the algorithm rather than using multiple AV nodal blocking agents that may worsen bradycardia. 4
• Avoid high doses of beta-blockers and calcium channel blockers as they may cause severe bradycardia. 4

Pre-Excited SVT (Wolff-Parkinson-White)

• If pre-excited AF develops, use synchronized cardioversion for unstable patients or intravenous procainamide/ibutilide for stable patients. 1
• Never use AV nodal blocking agents (adenosine, verapamil, diltiazem, beta-blockers) in pre-excited AF—they can accelerate ventricular rate and cause ventricular fibrillation. 1, 4

Common Pitfalls to Avoid

• Atrial or ventricular premature complexes immediately after successful conversion (whether by adenosine, cardioversion, or other means) may reinitiate SVT—have antiarrhythmic drugs ready if this occurs. 1
• Automatic tachycardias (ectopic atrial tachycardia, multifocal atrial tachycardia) will not respond to cardioversion and require different treatment approaches focused on rate control and treating underlying conditions. 4
• Standard Valsalva without postural modification has only 5-20% success rate—always use the modified technique with leg elevation. 5, 2, 3
• Ensure adequate IV access and saline flush preparation before adenosine administration—inadequate flush technique reduces effectiveness. 4