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

Initial Management of Supraventricular Tachycardia

Begin with immediate hemodynamic assessment, then proceed with vagal maneuvers in stable patients or direct cardioversion in unstable patients, followed by adenosine if vagal maneuvers fail. 1, 2

Immediate Hemodynamic Assessment

The first critical decision point is determining hemodynamic stability—unstable patients require immediate synchronized cardioversion without attempting vagal maneuvers or medications. 2

• Hemodynamically unstable patients (hypotension, altered mental status, chest pain, acute heart failure) should proceed directly to synchronized cardioversion at 50-100 J biphasic energy 2
• Stable patients can proceed through the stepwise algorithm below 1

First-Line Treatment: Vagal Maneuvers (Hemodynamically Stable Patients)

Vagal maneuvers are Class I, Level B recommendations and should be attempted immediately in all stable patients before any pharmacologic intervention. 1, 2

Modified Valsalva Maneuver (Most Effective)

• The modified Valsalva maneuver is significantly more effective than standard carotid sinus massage and should be the preferred initial vagal technique. 2, 3
• Technique: Patient bears down against a closed glottis for 10-30 seconds (generating 30-40 mm Hg intrathoracic pressure) while supine, then immediately lies flat with legs elevated 1, 2
• The modified version has a SUCRA value of 0.9992 for initial response, with a relative risk of 5.47 compared to carotid sinus massage 3

Alternative Vagal Maneuvers

• Carotid sinus massage: Apply steady pressure over right or left carotid sinus for 5-10 seconds after confirming absence of bruit by auscultation 1
• Ice-cold wet towel to face (diving reflex) 1
• Overall success rate when switching between techniques reaches 27.7% 1
• Never apply pressure to the eyeball—this practice is dangerous and abandoned 1

Second-Line Treatment: Adenosine

If vagal maneuvers fail, adenosine is the next intervention with 90-95% effectiveness for terminating SVT and is a Class I, Level B recommendation. 1, 2, 4

Adenosine Administration Protocol

• Standard dose: 6 mg rapid IV push through a large peripheral vein, followed immediately by 20 mL saline flush 2
• If first dose fails, give 12 mg rapid IV push 2
• Adenosine terminates approximately 95% of AVNRT cases 1
• Have electrical cardioversion equipment immediately available at bedside during administration 2

Critical Dosing Adjustments

• Reduce to 3 mg for patients taking dipyridamole, carbamazepine, or with transplanted hearts 2
• Larger doses may be needed with theophylline, caffeine, or theobromine 2
• Adenosine is absolutely contraindicated in asthma patients due to risk of severe bronchoconstriction 2

Third-Line Treatment: Alternative Pharmacologic Agents (If Adenosine Fails)

Intravenous beta blockers, diltiazem, or verapamil are reasonable (Class IIa, Level B) for hemodynamically stable patients when adenosine fails. 1

Calcium Channel Blockers

• Diltiazem and verapamil are particularly effective for converting AVNRT to sinus rhythm 1
• Critical safety warning: Never use verapamil or diltiazem in patients with wide-complex tachycardia, suspected ventricular tachycardia, pre-excited atrial fibrillation, or systolic heart failure—these can cause hemodynamic collapse or precipitate ventricular fibrillation 1, 2

Beta Blockers

• Esmolol is less effective than diltiazem but has an excellent safety profile 1
• Reasonable to attempt in hemodynamically stable patients 1

Synchronized Cardioversion

Synchronized cardioversion is Class I, Level B for both unstable patients (immediate) and stable patients who fail pharmacologic therapy. 1, 2

• Unstable patients: Immediate cardioversion without attempting other interventions 1, 2
• Stable patients: After failed vagal maneuvers and adenosine 1
• Initial energy: 50-100 J biphasic, increase stepwise if initial shock fails 2
• Provide adequate sedation/anesthesia in stable patients before cardioversion 2

Critical Diagnostic Considerations During Treatment

Record a 12-lead ECG to differentiate tachycardia mechanisms, particularly to distinguish wide-complex tachycardia (which may be ventricular tachycardia) from SVT with aberrancy. 1

• Adenosine serves dual diagnostic and therapeutic roles—it will unmask atrial activity in atrial flutter or atrial tachycardia while terminating AVNRT 1
• If QRS duration >120 ms, distinguish VT from SVT with aberrant conduction before administering AV nodal blocking agents 1
• Automatic tachycardias (ectopic atrial tachycardia, multifocal atrial tachycardia, junctional tachycardia) will not respond to cardioversion and require rate control instead 2

Common Pitfalls to Avoid

• Never use AV nodal blocking agents in patients with known accessory pathways or wide-complex tachycardia of uncertain etiology—this can precipitate ventricular fibrillation 2
• Do not use verapamil or diltiazem in suspected systolic heart failure 1, 2
• Avoid performing vagal maneuvers with patient upright—supine position is essential 1
• Do not delay cardioversion in hemodynamically unstable patients to attempt vagal maneuvers or medications 2

Post-Conversion Management

All patients treated for SVT should be referred to a heart rhythm specialist for long-term management decisions, which may range from conservative observation to catheter ablation depending on symptom frequency and patient preference. 5