What is the next step in managing a 22-year-old patient with new onset palpitations, no chest pain (CP), dizziness, or shortness of breath (SOB), normal vitals except for tachycardia with a heart rate of 180 beats per minute, and an electrocardiogram (ECG) showing narrow complex tachycardia?

Management of Narrow Complex Tachycardia in a Hemodynamically Stable Young Patient

In this hemodynamically stable 22-year-old with regular narrow complex tachycardia at 180 bpm, the next step is to obtain a 12-lead ECG during tachycardia (if not already done), then attempt vagal maneuvers, followed by IV adenosine if vagal maneuvers fail. 1, 2

Immediate Diagnostic Priorities

A 12-lead ECG during tachycardia is essential and should be obtained immediately, but should not delay therapy if hemodynamic instability develops. 1 At minimum, a monitor strip should be captured before any intervention. 1

• The narrow QRS complex (<120 ms) with regular rhythm indicates this is almost certainly supraventricular tachycardia (SVT), most likely atrioventricular nodal reentrant tachycardia (AVNRT) or atrioventricular reciprocating tachycardia (AVRT). 1, 2, 3
• The sudden onset of regular palpitations strongly suggests AVNRT or AVRT rather than sinus tachycardia, which accelerates and terminates gradually. 1, 2
• Look specifically for P waves: if no P waves are visible with regular RR intervals, AVNRT is most likely; if P waves are present in the ST segment separated from QRS by >70 ms, AVRT is most likely. 1, 2, 3
• Pseudo r' wave in lead V1 and pseudo S waves in inferior leads (II, III, aVF) are pathognomonic for AVNRT. 1, 2

Acute Management Algorithm for Hemodynamically Stable Patient

Step 1: Vagal Maneuvers

• Attempt vagal maneuvers first as they may terminate the arrhythmia and further support a reentrant tachycardia involving AV nodal tissue. 1, 2, 4, 5
• The Valsalva maneuver is safer and more efficacious than carotid massage, especially in elderly patients. 6
• Record a 12-lead ECG during vagal maneuver attempts to observe the response. 1, 2

Step 2: IV Adenosine

• If vagal maneuvers fail, adenosine is the first-line pharmacologic agent for acute termination of narrow complex tachycardia. 6, 4, 5, 7
• Adenosine should be administered as a rapid IV push (6 mg initially, followed by 12 mg if needed). 6, 4
• Record a 12-lead ECG during adenosine administration as the response aids in differential diagnosis. 1, 2
• Adenosine is contraindicated in second- or third-degree AV block, sick sinus syndrome, bronchospastic lung disease (asthma), and known hypersensitivity. 8

Step 3: Alternative Pharmacologic Agents

• If adenosine fails or is contraindicated, calcium channel blockers (diltiazem or verapamil) or beta blockers (metoprolol) can be used acutely. 4, 5, 7

Critical Safety Considerations

Hemodynamic stability must be continuously reassessed. If the patient becomes hemodynamically unstable at any point (hypotension, altered mental status, chest pain suggesting ischemia, acute heart failure), immediate synchronized DC cardioversion is indicated starting at 100-200 joules. 1, 9

Important Caveats About Adenosine Use

• Use adenosine with extreme caution if the diagnosis is uncertain, particularly if there is any possibility of atrial fibrillation with pre-excitation (Wolff-Parkinson-White syndrome), as adenosine may precipitate ventricular fibrillation in this setting. 9
• Methylxanthines (caffeine, aminophylline, theophylline) interfere with adenosine activity, while dipyridamole increases its activity. 8
• Common adverse reactions include flushing, chest discomfort, shortness of breath, headache, and throat/neck/jaw discomfort. 8

Post-Conversion Management

Once sinus rhythm is restored:

• Obtain a 12-lead ECG in normal sinus rhythm to look for pre-excitation (short PR interval, delta wave, wide QRS). 1, 9, 2
• If delta waves are present, this confirms Wolff-Parkinson-White syndrome and requires immediate referral to an arrhythmia specialist due to risk of sudden death. 1, 9
• All patients with documented SVT should be referred to a cardiac arrhythmia specialist for consideration of electrophysiologic study and catheter ablation, which has >95% success rate and is curative. 1, 9, 5, 7

Common Pitfalls to Avoid

• Do not rely on automatic ECG interpretation systems, as they are unreliable and commonly suggest incorrect arrhythmia diagnoses. 1, 2
• Do not assume hemodynamic stability rules out ventricular tachycardia if the QRS is wide—stable vital signs during tachycardia are not helpful for distinguishing SVT from VT. 1
• Do not give verapamil or diltiazem for wide complex tachycardia of uncertain etiology, as these may precipitate hemodynamic collapse if the rhythm is ventricular tachycardia. 1
• In this young patient with no chest pain, dizziness, or dyspnea and normal vitals except tachycardia, the rhythm is almost certainly SVT, but continuous monitoring is essential. 6, 4