What is the treatment for paroxysmal short runs of Supraventricular Tachycardia (SVT)?

Treatment of Paroxysmal Short Runs of SVT

For hemodynamically stable patients with paroxysmal short runs of SVT, initiate vagal maneuvers immediately, followed by IV adenosine 6 mg rapid push if vagal maneuvers fail, with synchronized cardioversion reserved for hemodynamically unstable patients or those who fail pharmacologic therapy. 1

Acute Management Algorithm

First-Line: Vagal Maneuvers

• Perform vagal maneuvers as the initial intervention (Class I recommendation) 1
• The modified Valsalva maneuver is most effective, with success rates up to 43% and superior efficacy compared to standard carotid sinus massage 2, 3
• Technique: Patient in supine position, bearing down against closed glottis for 10-30 seconds, generating at least 30-40 mmHg intrathoracic pressure 1
• Alternative: Apply ice-cold wet towel to face (diving reflex) or carotid sinus massage for 5-10 seconds after confirming absence of bruit 1
• Vagal maneuvers terminate up to 25% of PSVTs and should be attempted before any pharmacologic intervention 1

Second-Line: Adenosine

• If vagal maneuvers fail, administer adenosine 6 mg IV rapid push through large (antecubital) vein followed by 20 mL saline flush (Class I, LOE B) 1
• Adenosine terminates 90-95% of reentrant SVTs (AVNRT, orthodromic AVRT) 1
• If no conversion within 1-2 minutes, give 12 mg rapid IV push using same technique 1
• Have defibrillator immediately available when administering adenosine due to risk of precipitating atrial fibrillation with rapid ventricular response, particularly in patients with WPW syndrome 1, 4

Critical Adenosine Dosing Adjustments:

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given via central venous access 1
• Larger doses may be required for patients with significant theophylline, caffeine, or theobromine levels 1
• Contraindicated in patients with asthma due to risk of bronchoconstriction 1, 4
• Common transient side effects include flushing, dyspnea, and chest discomfort (30% of patients) 1, 4

Third-Line: Longer-Acting AV Nodal Blockers

• If adenosine fails or SVT recurs, use calcium channel blockers (verapamil 2.5-5 mg IV or diltiazem) or beta-blockers (Class IIa, LOE B) 1
• These agents provide more sustained rhythm control and are particularly useful when adenosine unmasks atrial fibrillation or flutter requiring rate control 1
• Critical caveat: Do NOT use verapamil or diltiazem if pre-excitation (WPW) is present or suspected, as this can precipitate ventricular fibrillation 1, 5
• Avoid in patients with severe left ventricular dysfunction (ejection fraction <30%) or moderate-to-severe heart failure 5

Emergency Intervention: Synchronized Cardioversion

• Immediate synchronized cardioversion for hemodynamically unstable patients (Class I recommendation) 1
• Initial biphasic energy: 50-100 J for SVT (120-200 J for atrial fibrillation), increase stepwise if unsuccessful 1
• Also indicated for hemodynamically stable patients when pharmacologic therapy fails or is contraindicated 1

Special Considerations for Short Runs

Automatic Tachycardias

• Ectopic atrial tachycardia, multifocal atrial tachycardia (MAT), and junctional tachycardia have gradual onset/termination (unlike abrupt reentrant SVTs) 1
• These arrhythmias are NOT responsive to cardioversion 1
• Vagal maneuvers and adenosine may transiently slow ventricular rate for diagnostic purposes but will not terminate these rhythms 1
• Treat with AV nodal blocking agents (beta-blockers, calcium channel blockers) for rate control rather than rhythm conversion 1

Post-Conversion Management

• Monitor closely for recurrence after successful conversion 1
• Treat recurrent episodes with adenosine or longer-acting AV nodal blocking agents (diltiazem or beta-blocker) 1
• Patients may develop atrial or ventricular premature complexes immediately after conversion that can reinitiate tachycardia, requiring antiarrhythmic prophylaxis 1

Common Pitfalls to Avoid

1. Never administer verapamil or diltiazem for wide-complex tachycardia until VT is definitively excluded—this can cause hemodynamic collapse or ventricular fibrillation 1, 5

2. Do not use AV nodal blockers in pre-excited atrial fibrillation (WPW with AF)—use procainamide or ibutilide instead, or proceed directly to cardioversion 1

3. Ensure proper adenosine administration technique: rapid push through large peripheral vein with immediate saline flush—slow administration reduces efficacy 1

4. Recognize that short, self-terminating runs may not require acute intervention if hemodynamically tolerated, but warrant evaluation for ongoing management strategies 2, 6

5. Have resuscitation equipment immediately available before administering adenosine, as fatal cardiac arrest and ventricular arrhythmias have been reported 4