What is the initial treatment for a patient with Supraventricular Tachycardia (SVT)?

Initial Treatment for Supraventricular Tachycardia (SVT)

Begin with vagal maneuvers immediately in hemodynamically stable patients, specifically the modified Valsalva maneuver performed supine for 10-30 seconds generating 30-40 mmHg intrathoracic pressure, which is 2.8-3.8 times more effective than standard Valsalva. 1, 2

First-Line: Vagal Maneuvers

• Position the patient supine before attempting any vagal maneuver 2
• The modified Valsalva maneuver is the most effective vagal technique, with superior efficacy compared to carotid sinus massage 2
• Have the patient bear down against a closed glottis for 10-30 seconds, generating at least 30-40 mmHg pressure 1
• If Valsalva fails, attempt carotid sinus massage for 5-10 seconds after confirming absence of carotid bruits by auscultation 1, 2
• Alternative techniques include applying ice-cold wet towels to the face (diving reflex) 1
• Vagal maneuvers successfully terminate approximately 25-28% of paroxysmal SVT (PSVT) cases 1

Second-Line: Adenosine

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

• Adenosine terminates AVNRT in approximately 90-95% of cases 1, 2
• If no conversion within 1-2 minutes, give 12 mg rapid IV push using the same technique 1
• Have a defibrillator immediately available when administering adenosine, particularly if Wolff-Parkinson-White syndrome is suspected 1
• 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 in patients with significant theophylline, caffeine, or theobromine levels 1
• Do not give adenosine to patients with asthma 1
• Common transient side effects include flushing, dyspnea, and chest discomfort 1

Third-Line: IV Calcium Channel Blockers or Beta-Blockers

For hemodynamically stable patients who fail adenosine, use IV diltiazem or verapamil, which achieve 80-98% success rates. 1, 2

• IV diltiazem and verapamil are particularly effective for converting AVNRT to sinus rhythm 1
• Absolutely ensure the rhythm is not ventricular tachycardia or pre-excited atrial fibrillation before administering these agents, as they can cause hemodynamic collapse and ventricular fibrillation 1, 2
• Avoid diltiazem or verapamil in patients with suspected systolic heart failure 1
• IV beta-blockers (such as esmolol) are reasonable alternatives with excellent safety profiles, though diltiazem is more effective 1, 3
• Esmolol is FDA-approved for rapid ventricular rate control in atrial fibrillation/flutter and noncompensatory sinus tachycardia in emergent circumstances 3

Immediate Cardioversion

Perform synchronized cardioversion immediately in hemodynamically unstable patients, or when pharmacological therapy fails or is contraindicated in stable patients. 1

• Use initial energy of 50-100 J for SVT with biphasic waveforms 1, 2
• Increase dose stepwise if initial shock fails 1
• Synchronized cardioversion is highly effective, terminating SVT in the vast majority of cases 1
• For monophasic waveforms, begin at 200 J and increase stepwise 1

Critical Pitfalls to Avoid

• Never give calcium channel blockers or beta-blockers to patients with pre-excited atrial fibrillation (Wolff-Parkinson-White with AF)—this requires immediate cardioversion, not AV nodal blockade 2
• Do not perform carotid massage without first confirming absence of bruits 1, 2
• Automatic tachycardias (ectopic atrial tachycardia, multifocal atrial tachycardia, junctional tachycardia) are not responsive to cardioversion and require rate-controlling drugs 1
• Vagal maneuvers and adenosine only transiently slow atrial fibrillation or flutter but will not terminate these rhythms 1
• Monitor for recurrence after successful conversion and be prepared to re-treat 1