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

Treatment of Paroxysmal Supraventricular Tachycardia

For hemodynamically stable patients with paroxysmal SVT, perform vagal maneuvers immediately as first-line treatment, followed by IV adenosine 6 mg if vagal maneuvers fail; for hemodynamically unstable patients, proceed directly to synchronized cardioversion. 1, 2

Initial Assessment: Hemodynamic Stability

Determine hemodynamic stability immediately - unstable patients show hypotension, altered mental status, signs of shock, chest pain, or acute heart failure. 2

• If hemodynamically unstable: Proceed directly to synchronized cardioversion (Class I recommendation). 1, 2
• If hemodynamically stable: Follow the stepwise algorithm below. 1

Acute Management Algorithm for Stable Patients

Step 1: Vagal Maneuvers (First-Line)

Perform vagal maneuvers with the patient in the supine position - this is the recommended first-line intervention with a 27.7% overall success rate when switching between techniques. 1, 3

Specific techniques include:

• Modified Valsalva maneuver: Patient bears down against a closed glottis for 10-30 seconds, generating at least 30-40 mm Hg intrathoracic pressure. 1, 2
• Carotid sinus massage: Apply steady pressure over the right or left carotid sinus for 5-10 seconds only after confirming absence of carotid bruits by auscultation. 1, 3
• Diving reflex: Apply an ice-cold, wet towel to the face. 1, 3

Critical pitfall: Never apply pressure to the eyeball - this practice is dangerous and has been abandoned. 1, 3

Step 2: IV Adenosine (If Vagal Maneuvers Fail)

Adenosine is the first-line pharmacologic agent with 91-95% effectiveness for terminating AVNRT and AVRT. 1, 2, 4

Dosing protocol (American Heart Association):

• Initial dose: 6 mg IV push via large proximal vein, followed immediately by 20 mL saline flush. 2
• If no conversion within 1-2 minutes: 12 mg IV push with saline flush. 2
• If still no conversion: May repeat 12 mg IV push one more time. 2

Dose modifications:

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access. 2
• Increase dose for patients with significant blood levels of theophylline, caffeine, or theobromine. 2

Absolute contraindication: Do not give adenosine to patients with asthma due to risk of severe bronchospasm. 2, 3

Safety: Have a defibrillator available when administering adenosine if Wolff-Parkinson-White syndrome is a consideration, as adenosine may initiate atrial fibrillation with rapid ventricular rates. 2

Common side effects: Flushing, dyspnea, and chest discomfort (transient, lasting <60 seconds). 2, 5

Step 3: IV Calcium Channel Blockers or Beta-Blockers (If Adenosine Fails)

For patients in whom adenosine fails or is contraindicated (e.g., asthma), use IV calcium channel blockers or beta-blockers (Class IIa recommendation). 1, 3

• IV diltiazem: 15-20 mg over 2 minutes (64-98% conversion rate). 2
• IV verapamil: 2.5-5 mg over 2 minutes. 2
• IV beta-blockers: Class IIa recommendation, though less effective than calcium channel blockers. 3

Critical caveat: Avoid AV nodal blocking agents (verapamil, diltiazem, beta-blockers) in patients with suspected pre-excitation (Wolff-Parkinson-White syndrome), as they may accelerate ventricular rate and precipitate ventricular fibrillation. 3

Step 4: IV Amiodarone or Synchronized Cardioversion

If all pharmacologic therapy is ineffective or contraindicated, proceed to:

• IV amiodarone (Class IIb recommendation). 1
• Synchronized cardioversion (Class I recommendation for stable patients when pharmacologic therapy fails). 1

Post-Conversion Management

Monitor continuously for recurrence - patients commonly experience atrial or ventricular premature complexes that may trigger recurrent SVT within seconds to minutes. 2

If immediate recurrence occurs:

• Treat with adenosine again, or
• Consider longer-acting AV nodal blocking agent (diltiazem or beta-blocker). 2

Long-Term Management

Catheter ablation is recommended as first-line therapy for preventing recurrent symptomatic PSVT, with single-procedure success rates of 94.3-98.5% and low complication rates. 1, 4, 6

Alternative pharmacologic options for patients who decline or are not candidates for ablation:

• Oral beta-blockers, diltiazem, or verapamil (Class IIb for acute treatment, reasonable for long-term prevention). 1, 3
• Flecainide or propafenone for patients without structural heart disease. 3

Patient education: Teach vagal maneuvers for self-termination of future episodes. 2, 3

Special Population: Pregnancy

Adenosine is safe and effective during pregnancy and should be used as first-line pharmacologic therapy. 2