What is the initial treatment approach for a patient experiencing supraventricular tachycardia (SVT)?

Initial Treatment of Supraventricular Tachycardia

For acute SVT, immediately perform vagal maneuvers as first-line treatment, followed by adenosine 6 mg rapid IV push if vagal maneuvers fail, and proceed to synchronized cardioversion for hemodynamically unstable patients. 1, 2, 3

Immediate Assessment and First-Line Treatment

Vagal Maneuvers (Perform First)

• The modified Valsalva maneuver is the most effective vagal technique with the patient supine, bearing down against a closed glottis for 10-30 seconds (equivalent to 30-40 mmHg pressure), then immediately lying flat with legs raised 1, 2, 4
• The modified Valsalva demonstrates superior effectiveness compared to standard carotid sinus massage, with a 5.47-fold higher initial conversion rate 4
• Carotid sinus massage is an alternative: apply steady pressure over the carotid sinus for 5-10 seconds only after confirming absence of carotid bruits by auscultation 1, 5, 3
• Cold stimulus (ice-cold wet towel to face) triggers the diving reflex and serves as another vagal option 1, 5
• Switching between vagal techniques achieves an overall success rate of 27.7% 1, 3
• Never apply pressure to the eyeball—this practice is dangerous and abandoned 1, 3

Second-Line Pharmacological Treatment

Adenosine (First-Line Medication)

• Administer adenosine 6 mg rapid IV bolus through a large vein, followed immediately by saline flush if vagal maneuvers fail 1, 2, 5
• Adenosine terminates AVNRT in approximately 90-95% of patients 1, 2, 3
• Prepare for cardioversion as adenosine may precipitate atrial fibrillation 5
• Adenosine is safe during pregnancy due to its short half-life 2

Alternative Medications for Hemodynamically Stable Patients

• Intravenous diltiazem or verapamil are highly effective for converting AVNRT to sinus rhythm (Class IIa recommendation) 1, 3
• Intravenous beta blockers are reasonable but less effective than calcium channel blockers 1, 3
• Critical caveat: Avoid verapamil, diltiazem, and beta blockers in patients with pre-excited atrial fibrillation, ventricular tachycardia, or systolic heart failure—these can cause hemodynamic collapse or ventricular fibrillation 1, 5, 3

Hemodynamically Unstable Patients

Immediate Cardioversion

• Perform synchronized cardioversion immediately for hemodynamically unstable patients when vagal maneuvers and adenosine fail or are not feasible (Class I recommendation) 1, 2, 3
• Initial energy: 50-100 joules for SVT 5
• Synchronized cardioversion is safe at all stages of pregnancy if necessary 2

Special Populations and Situations

Pre-Excitation (Wolff-Parkinson-White)

• Avoid all AV nodal blocking agents (adenosine, verapamil, diltiazem, beta blockers) in patients with suspected pre-excitation 2, 3
• For hemodynamically stable pre-excited AF: use ibutilide or IV procainamide (Class I recommendation) 2, 3
• For hemodynamically unstable pre-excited AF: immediate synchronized cardioversion 3

Patients with Low Baseline Heart Rate

• Vagal maneuvers remain safe as first-line treatment 5
• Consider reduced adenosine dosing and earlier cardioversion rather than rate-controlling medications 5
• Avoid high doses of AV nodal blocking agents that may exacerbate bradycardia 5

Critical Diagnostic Step

• Always obtain a 12-lead ECG to distinguish SVT from ventricular tachycardia before initiating treatment—this is essential to avoid catastrophic outcomes from inappropriate calcium channel blocker or beta blocker administration in VT 2, 3

Common Pitfalls to Avoid

• Do not use verapamil or diltiazem in patients with systolic heart failure—risk of hemodynamic decompensation 1
• Do not perform carotid massage without first auscultating for bruits 1, 3
• Automatic tachycardias (ectopic atrial tachycardia, multifocal atrial tachycardia) may not respond to cardioversion and require different approaches 5
• Ensure proper ECG diagnosis before treatment to avoid treating VT as SVT 3