What is the next best step in managing a patient with Paroxysmal Supraventricular Tachycardia (PSVT)?

Management of Paroxysmal Supraventricular Tachycardia (PSVT)

Begin with vagal maneuvers immediately, followed by adenosine 6 mg IV rapid push if vagal maneuvers fail, and proceed to synchronized cardioversion only if the patient is hemodynamically unstable or pharmacologic therapy fails. 1

Initial Assessment and Stabilization

Determine hemodynamic stability first - assess for hypotension, altered mental status, chest pain, acute heart failure, or signs of shock. 1

• Hemodynamically unstable patients require immediate synchronized cardioversion at 50-100 J (biphasic), increasing stepwise if initial shock fails 1, 2
• Hemodynamically stable patients proceed with the vagal-adenosine algorithm below 1

First-Line Treatment: Vagal Maneuvers

Perform vagal maneuvers as the immediate first intervention - these terminate up to 25-28% of PSVT episodes and should be attempted before any pharmacologic therapy. 1, 2

Specific Techniques (in order of preference):

• Valsalva maneuver: Patient bears down against closed glottis for 10-30 seconds (equivalent to 30-40 mm Hg intrathoracic pressure) in the supine position 1
• 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 towel to face: Apply ice-cold, wet towel to activate diving reflex 1

Critical caveat: Valsalva is more successful than carotid massage, and switching between techniques achieves a 27.7% overall success rate. 1 Never apply pressure to the eyeball - this is dangerous and abandoned. 1

Second-Line Treatment: Adenosine

If vagal maneuvers fail, immediately administer adenosine 6 mg IV rapid push through a large proximal vein (antecubital preferred) followed by 20 mL saline flush. 1, 2

Adenosine Dosing Protocol:

• Initial dose: 6 mg IV rapid push + 20 mL saline flush 1, 3
• Second dose: If no conversion within 1-2 minutes, give 12 mg IV rapid push + flush 1, 3
• Third dose: May repeat 12 mg once more if needed 3
• Success rate: Terminates 90-95% of PSVT (AVNRT and orthodromic AVRT) 1, 3

Dose Modifications:

• Reduce to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given via central venous access 1, 3, 4
• Increase dose may be needed for patients with significant theophylline, caffeine, or theobromine levels 1, 3, 4

Absolute Contraindications to Adenosine:

• Second- or third-degree AV block (without pacemaker) 4
• Sick sinus syndrome or symptomatic bradycardia (without pacemaker) 4
• Asthma or bronchospastic lung disease - adenosine causes bronchoconstriction and respiratory compromise 1, 3, 4
• Known hypersensitivity to adenosine 4

Critical Safety Measures:

Have a defibrillator immediately available when administering adenosine, as it may precipitate atrial fibrillation with rapid ventricular rates in 1-15% of patients, particularly dangerous in Wolff-Parkinson-White syndrome. 1, 2, 3

Monitor continuously during and after administration - patients commonly develop atrial or ventricular premature complexes immediately after conversion that may trigger recurrent PSVT episodes. 1, 2, 3

Common transient side effects (<1 minute duration): flushing, dyspnea, chest discomfort occur in ~30% of patients. 1, 3, 4

Third-Line Treatment: Calcium Channel Blockers

If adenosine fails or is contraindicated (except in asthma where CCBs are preferred), administer IV diltiazem or verapamil. 1, 2

• These agents have 80-98% success rates for PSVT termination 1
• Diltiazem and verapamil are highly effective alternatives with longer duration of action than adenosine 2, 5
• Critical warning: Never give IV calcium channel blockers and beta-blockers concomitantly - this causes severe hypotension and bradycardia 2

Fourth-Line Treatment: Beta-Blockers

IV beta-blockers are reasonable but less effective than diltiazem for acute PSVT termination in stable patients. 2

Synchronized Cardioversion

Perform synchronized cardioversion for:

• Hemodynamically unstable patients when vagal maneuvers/adenosine fail or are not feasible 1, 2
• Hemodynamically stable patients when all pharmacologic therapy fails or is contraindicated 1

Energy settings: Start at 50-100 J (biphasic), increase stepwise if unsuccessful 1, 2

Post-Conversion Management

Monitor continuously for recurrence - atrial/ventricular premature complexes after conversion commonly trigger immediate PSVT reinitiation. 1, 2, 3

For recurrent episodes: Treat with repeat adenosine or initiate longer-acting AV nodal blocking agent (diltiazem or beta-blocker) for sustained rate control. 1, 2, 3

If adenosine unmasks atrial fibrillation or flutter: Transition to longer-acting AV nodal blocking agent for ventricular rate control. 1, 3

Special Population: Wolff-Parkinson-White Syndrome

Critical distinction: If pre-excited atrial fibrillation is suspected (wide, irregular QRS), NEVER use AV nodal blocking agents (adenosine, calcium channel blockers, beta-blockers, digoxin) - these can precipitate ventricular fibrillation. 1, 2

Management of pre-excited AF:

• Unstable: Immediate synchronized cardioversion 1, 2
• Stable: IV procainamide or ibutilide 1, 2

Common Pitfalls to Avoid

• Never start with 12 mg adenosine - 70% of patients convert with 6 mg or less, and side effects are dose-dependent 3
• Never give adenosine to asthmatics - use calcium channel blockers instead 1, 3, 4
• Never combine IV calcium channel blockers with IV beta-blockers - severe hemodynamic compromise results 2
• Never use AV nodal blockers in wide-complex irregular tachycardia - assume pre-excited AF until proven otherwise 1, 2
• Never perform carotid massage without first auscultating for bruits - risk of stroke 1

Pregnancy Considerations

Adenosine is safe and effective in pregnancy and remains the drug of choice after vagal maneuvers. 1, 3