What is the first‑line treatment for a patient with symptomatic supraventricular tachycardia?

First-Line Treatment for Symptomatic SVT

For hemodynamically stable patients with symptomatic supraventricular tachycardia, vagal maneuvers—specifically the modified Valsalva maneuver—should be attempted first, followed immediately by intravenous adenosine 6 mg rapid push if vagal maneuvers fail. 1, 2

Immediate Hemodynamic Assessment

• Proceed directly to synchronized cardioversion (50–100 J) without attempting vagal maneuvers or medications if the patient exhibits hypotension, altered mental status, shock, chest pain, or acute heart failure—this restores sinus rhythm in nearly 100% of unstable cases. 1, 3, 2

First-Line: Vagal Maneuvers (Hemodynamically Stable Patients)

• The modified Valsalva maneuver is the most effective vagal technique, achieving conversion in approximately 43% of attempts, compared to 27% overall success across all vagal methods. 1, 2

• Technique: Patient lies supine and bears down against a closed glottis for 10–30 seconds (generating 30–40 mmHg intrathoracic pressure), then immediately lies flat with legs elevated. 1, 2

• Carotid sinus massage is an acceptable alternative: apply steady pressure over the carotid sinus for 5–10 seconds after confirming absence of a bruit; avoid in elderly patients or those with known carotid disease. 1, 2

• Ice-water facial immersion (cold wet towel on the face) activates the diving reflex and may terminate SVT. 1

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

Second-Line: Adenosine (When Vagal Maneuvers Fail)

• Adenosine is the first-line pharmacologic agent, terminating 90–95% of AVNRT and 78–96% of AVRT episodes. 1, 3, 2

Standard 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, 3, 2

• Second dose: If no conversion within 1–2 minutes, give 12 mg rapid IV push with saline flush. 1, 3, 2

• Third dose: A second 12 mg dose may be administered if needed (maximum cumulative dose 30 mg). 1, 3

Dose Adjustments

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, cardiac transplant recipients, or when administered via central venous access. 1, 2

• Increase dose in patients with high caffeine, theophylline, or theobromine levels, which act as competitive adenosine antagonists. 1, 2

Absolute Contraindications

• Asthma or active bronchospasm—risk of severe bronchospasm. 1, 3, 2

• Second- or third-degree AV block or sick-sinus syndrome without a pacemaker. 1, 3

• Pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White)—risk of precipitating rapid ventricular response and ventricular fibrillation. 1, 3

Safety Considerations

• A defibrillator must be immediately available when administering adenosine, particularly if Wolff-Parkinson-White syndrome is a consideration. 1, 3

• Common transient side effects (<60 seconds): flushing, dyspnea, chest discomfort, transient AV block. 1

Third-Line: Alternative Pharmacologic Agents (Adenosine Contraindicated or Failed)

• Intravenous diltiazem 15–20 mg over 2 minutes is the preferred alternative, achieving 64–98% conversion; particularly effective for patients with asthma or COPD. 1, 3

• Intravenous verapamil 2.5–5 mg over 2 minutes is an acceptable alternative calcium-channel blocker, with clinical effect typically within 3–5 minutes. 1, 3

• Intravenous beta-blockers (metoprolol 2.5–5 mg every 2–5 minutes, maximum 15 mg; or esmolol) are reasonable alternatives with excellent safety profiles, though slightly less effective than calcium-channel blockers. 1, 3

Critical Contraindications for Calcium-Channel Blockers

• Do NOT administer verapamil or diltiazem if: (1) ventricular tachycardia cannot be excluded, (2) pre-excited atrial fibrillation is present, (3) suspected systolic heart failure exists, or (4) the patient is hemodynamically unstable—these may precipitate ventricular fibrillation or cardiovascular collapse. 1, 3, 2

• Never combine IV calcium-channel blockers with IV beta-blockers due to synergistic hypotension and bradycardia. 1

Fourth-Line: Synchronized Cardioversion (Stable Patients)

• When all pharmacologic options fail or are contraindicated, elective synchronized cardioversion with appropriate sedation yields 80–98% success in hemodynamically stable patients. 1, 3, 2

Post-Conversion Management

• Continuous cardiac monitoring is essential immediately after conversion, as premature atrial or ventricular complexes frequently trigger recurrent SVT within seconds to minutes. 1, 3

• If immediate recurrence occurs, administer a longer-acting AV-nodal blocker (oral diltiazem or a beta-blocker) to prevent re-initiation. 1, 3

• If adenosine reveals atrial flutter or atrial tachycardia (by producing transient AV block without terminating the rhythm), manage with a longer-acting AV-nodal blocker for rate control rather than attempting rhythm conversion. 1

Special Population: Pregnancy

• Vagal maneuvers remain first-line in pregnant patients. 1

• Adenosine is safe and effective during pregnancy. 1

• If hemodynamically unstable, proceed to synchronized cardioversion. 1

Critical Pitfalls to Avoid

• Do not delay cardioversion in unstable patients to attempt vagal maneuvers or drug therapy. 1, 2

• Do not administer calcium-channel blockers when ventricular tachycardia or pre-excited atrial fibrillation is possible—this may precipitate ventricular fibrillation and death. 1, 3, 2

• Do not use adenosine in asthma patients due to severe bronchospasm risk. 1, 3, 2

• Always obtain a 12-lead ECG during tachycardia to differentiate SVT from VT and identify pre-excitation before administering any AV-nodal blocking agent. 1, 3