What is the appropriate emergency department management for a 23-year-old man presenting with supraventricular tachycardia and no known cardiac disease?

Emergency Department Management of SVT in a 23-Year-Old Male Without Cardiac History

Begin with vagal maneuvers immediately, followed by adenosine if unsuccessful, and proceed directly to synchronized cardioversion only if the patient becomes hemodynamically unstable. 1

Initial Assessment and Documentation

• Obtain a 12-lead ECG immediately to document the rhythm, differentiate SVT from ventricular tachycardia, and identify any pre-excitation pattern (delta wave, short PR interval) that would contraindicate certain medications. 1
• Assess hemodynamic stability by checking for signs of shock, altered mental status, chest pain, severe dyspnea, or hypotension—if any are present, skip pharmacologic therapy and proceed directly to synchronized cardioversion. 1
• Do not rely on automated ECG interpretation; these systems are unreliable and frequently misclassify arrhythmias. 1

Acute Treatment Algorithm for Hemodynamically Stable Patients

First-Line: Vagal Maneuvers (Class I Recommendation)

• Perform vagal maneuvers with the patient in the supine position, including Valsalva maneuver or carotid sinus massage. 1
• These terminate approximately 27.7% of SVT episodes and should be attempted before any medication. 2
• Never apply pressure to the eyeball—this is dangerous and abandoned. 2

Second-Line: Adenosine (Class I Recommendation)

• Adenosine is the definitive first-line pharmacologic agent with a 90-95% success rate in terminating SVT. 1, 3, 4
• Dosing protocol:
  • Initial dose: 6 mg rapid IV push through the most proximal IV line, followed immediately by saline flush
  • If no response after 1-2 minutes: 12 mg rapid IV push
  • If still no response: repeat 12 mg dose once more 1
• Continuous ECG monitoring and immediate defibrillator availability are mandatory during adenosine administration. 2
• Adenosine has a half-life of only seconds, so adverse effects (chest discomfort, dyspnea, flushing) are brief and self-limited. 3

Third-Line: IV Calcium Channel Blockers or Beta-Blockers (Class IIa Recommendation)

Critical caveat: Before administering these agents, you must confirm the absence of pre-excitation on the baseline ECG. 5

• IV diltiazem or verapamil can be effective for hemodynamically stable SVT if adenosine fails. 1
• IV beta-blockers are a reasonable alternative. 1
• Verapamil and diltiazem are absolutely contraindicated in patients with Wolff-Parkinson-White syndrome (pre-excitation pattern) because they can precipitate ventricular fibrillation. 5
• Verapamil carries warnings for severe hypotension, cardiogenic shock, and should not be given within hours of IV beta-blockers due to additive negative inotropic effects. 5
• Diltiazem may cause symptomatic hypotension in 3.2% of patients and can rarely cause high-degree AV block. 6

Last Resort: Synchronized Cardioversion (Class I Recommendation)

• Synchronized cardioversion is indicated when pharmacologic therapy is ineffective or contraindicated in hemodynamically stable patients. 1
• For hemodynamically unstable patients, proceed immediately to synchronized cardioversion at 0.5-1 J/kg without attempting medications. 1, 7

Critical Pitfalls to Avoid

• Do not administer verapamil or diltiazem if there is any suspicion of pre-excitation (even subtle delta waves on baseline ECG), as this can cause ventricular fibrillation and death. 5
• Do not administer verapamil or diltiazem for wide-complex tachycardia unless you are certain it is SVT with aberrancy—if it is ventricular tachycardia, these agents can cause marked hemodynamic deterioration and ventricular fibrillation. 1, 5
• Do not give IV beta-blockers and IV calcium channel blockers in close temporal proximity (within a few hours) due to additive negative inotropic and conduction effects. 5

Post-Conversion Management

• Maintain continuous cardiac monitoring after successful conversion to detect recurrence. 2
• Refer all patients to cardiology or cardiac electrophysiology for outpatient evaluation, as catheter ablation has a high success rate and is first-line for long-term management of recurrent symptomatic SVT. 1, 8
• If pre-excitation is present on the baseline ECG, immediate cardiology referral is mandatory due to sudden death risk, even if the patient is now asymptomatic. 1
• Educate the patient on vagal maneuvers (Valsalva, carotid massage) for self-management of future episodes. 1

Diagnostic Considerations for This Young Patient

• In a 23-year-old with no cardiac history, SVT most commonly represents atrioventricular nodal reentrant tachycardia (AVNRT) or atrioventricular reentrant tachycardia (AVRT), both of which respond well to adenosine. 1, 4, 8
• Obtain an echocardiogram to exclude structural heart disease, though physical examination and ECG usually cannot detect it. 1
• Check for precipitating factors including excessive caffeine, alcohol, nicotine, recreational drugs (especially stimulants), or hyperthyroidism. 1, 9