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

Initial Treatment of Paroxysmal Supraventricular Tachycardia (PSVT)

Begin with vagal maneuvers immediately, followed by intravenous adenosine if vagal maneuvers fail, and proceed to synchronized cardioversion for hemodynamically unstable patients or those who fail pharmacological therapy. 1

Immediate Assessment and First-Line Therapy

Vagal Maneuvers (First-Line)

• Perform vagal maneuvers as the initial intervention for all hemodynamically stable patients with PSVT, as they terminate up to 25-27.7% of episodes and can be performed quickly without medication 1
• Modified Valsalva maneuver: Have the patient bear down against a closed glottis for 10-30 seconds while supine, generating at least 30-40 mmHg of intrathoracic pressure 1
• Carotid sinus massage: After confirming absence of carotid bruits by auscultation, apply steady pressure over the right or left carotid sinus for 5-10 seconds 1
• Cold stimulus (diving reflex): Apply an ice-cold, wet towel to the face as an alternative vagal maneuver 1, 2
• The Valsalva maneuver is more successful than carotid sinus massage, and switching between techniques increases overall success rates 1

Adenosine (Second-Line Pharmacological Therapy)

If vagal maneuvers fail, adenosine is the preferred pharmacological agent with approximately 91-95% effectiveness in terminating PSVT 1, 3

Dosing Protocol:

• Initial dose: 6 mg rapid IV push through a large (antecubital) vein, followed immediately by a 20 mL saline flush 1, 4
• If no conversion within 1-2 minutes: Give 12 mg rapid IV push using the same technique 1
• If still no conversion: May repeat 12 mg dose once more 1

Critical Dosing Modifications:

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access 1
• Larger doses may be required for patients with significant blood levels of theophylline, caffeine, or theobromine 1

Important Safety Considerations:

• Have a defibrillator immediately available when administering adenosine, as it may precipitate atrial fibrillation with rapid ventricular rates, particularly in patients with Wolff-Parkinson-White syndrome 1, 2
• Contraindicated in patients with asthma due to risk of bronchoconstriction 1, 4
• Adenosine is safe and effective in pregnancy 1
• Common but transient side effects include flushing, dyspnea, and chest discomfort 1, 4

Alternative Pharmacological Agents

Calcium Channel Blockers and Beta-Blockers

If adenosine fails or PSVT recurs, longer-acting AV nodal blocking agents are reasonable alternatives for hemodynamically stable patients 1

Intravenous Verapamil or Diltiazem:

• These agents are particularly effective in converting PSVT to sinus rhythm with success rates of 80-98% 1
• Critical contraindications: Do not use in patients with pre-excited atrial fibrillation (Wolff-Parkinson-White syndrome), ventricular tachycardia, suspected systolic heart failure, or severe left ventricular dysfunction (ejection fraction <30%) 1, 5
• Verapamil carries risk of severe hypotension and should be avoided in patients with any degree of ventricular dysfunction if they are receiving beta-blockers 5

Intravenous Beta-Blockers:

• Reasonable alternative but limited evidence for effectiveness compared to calcium channel blockers 1
• Esmolol was less effective than diltiazem in comparative trials 1

Electrical Cardioversion

Hemodynamically Unstable Patients:

Perform immediate synchronized cardioversion when patients present with hypotension, altered mental status, signs of shock, ischemic chest discomfort, or acute heart failure 1

• Synchronized cardioversion should be performed if adenosine and vagal maneuvers fail or are not feasible 1
• Initial energy: 50-100 J for SVT, increasing in stepwise fashion if unsuccessful 2

Hemodynamically Stable Patients:

Synchronized cardioversion is recommended when pharmacological therapy fails to terminate the tachycardia or is contraindicated 1

• Cardioversion is highly effective in terminating PSVT in resistant cases 1

Critical Pitfalls and Caveats

Diagnostic Considerations:

• Always obtain a 12-lead ECG to confirm narrow-complex tachycardia, as ventricular tachycardia may masquerade as PSVT on single-lead monitoring 6
• Adenosine serves both therapeutic and diagnostic purposes by unmasking atrial activity in arrhythmias such as atrial flutter or atrial tachycardia 1

Automatic Tachycardias:

• Automatic arrhythmias (ectopic atrial tachycardia, multifocal atrial tachycardia, junctional tachycardia) are not responsive to cardioversion and require different treatment approaches focused on rate control with AV nodal blocking agents 1, 2

Special Populations:

• Patients with low baseline heart rates require careful monitoring and may need reduced dosing of rate-controlling medications, with earlier consideration of cardioversion 2
• Wolff-Parkinson-White syndrome with atrial fibrillation: Avoid AV nodal blocking agents (adenosine, calcium channel blockers, beta-blockers); use procainamide or immediate cardioversion instead 1, 5

Post-Conversion Management:

• Monitor for recurrence after successful conversion 1
• If PSVT recurs, treat with adenosine or initiate longer-acting AV nodal blocking agents (diltiazem or beta-blockers) for sustained rate control 1