A 32-year-old woman with known Wolff-Parkinson-White (WPW) syndrome presents to the emergency department with palpitations and dyspnea. On examination, heart rate is 180 bpm, BP 110/70 mmHg, and she is alert and hemodynamically stable. A 12-lead ECG shows a regular narrow-complex tachycardia with a rate of 180 bpm. What is the most appropriate immediate next step in management?

Explanation

## Clinical Context This patient has a regular narrow-complex tachycardia (orthodromic AVRT) in the setting of known WPW syndrome. She is hemodynamically stable (BP 110/70 mmHg, alert), which allows for a stepwise pharmacological approach. ## Management of Stable SVT: Stepwise Approach **Key Point:** Per ACC/AHA/HRS 2015 guidelines for SVT management, **vagal maneuvers are the recommended first-line intervention** for hemodynamically stable narrow-complex tachycardia (Class I, Level B-R). If vagal maneuvers fail, intravenous adenosine is the next step (Class I, Level B-R). Option D — "Vagal maneuvers followed by adenosine if unsuccessful" — correctly reflects this stepwise guideline-based approach. ## Why Vagal Maneuvers First? 1. **Non-invasive and immediate**: No IV access required; can be performed instantly 2. **Effective**: Modified Valsalva maneuver achieves cardioversion in ~40–50% of cases (REVERT trial, Appelboam et al., Lancet 2015) 3. **Guideline-endorsed**: ACC/AHA/HRS 2015 SVT guidelines explicitly recommend vagal maneuvers before pharmacotherapy in stable patients 4. **Safety**: No adverse drug effects; safe in WPW with narrow-complex tachycardia ## Adenosine in WPW (Narrow-Complex) **High-Yield:** In narrow-complex (orthodromic) AVRT in WPW, adenosine is **safe and effective** because the reentrant circuit depends on AV nodal conduction. Adenosine transiently blocks the AV node, terminating the circuit. It is the appropriate pharmacological step **after** vagal maneuvers fail. **Warning:** Adenosine should be used with caution if there is any possibility of pre-excited (wide-complex/antidromic) tachycardia or atrial fibrillation with WPW, as it can precipitate ventricular fibrillation in those settings. ## Why NOT Adenosine Alone (Option A) as the First Step? Administering adenosine without first attempting vagal maneuvers skips a guideline-recommended, non-invasive, effective first-line step. Option A is not wrong per se, but Option D represents the **most appropriate** best-next-step per current guidelines. ## Why NOT Verapamil (Option B)? - Second-line agent for SVT - **Contraindicated** in pre-excited AF or wide-complex tachycardia in WPW (risk of VF) - Slower onset than adenosine; sustained hemodynamic effects ## Why NOT DC Cardioversion (Option C)? DC cardioversion is reserved for hemodynamically **unstable** patients (hypotension, altered consciousness, pulmonary edema, ischemic chest pain). This patient is stable. | Intervention | Guideline Recommendation | Safety in WPW (narrow) | |---|---|---| | **Vagal maneuvers** | First-line (Class I) | Safe | | **Adenosine** | Second-line if vagal fails (Class I) | Safe | | **Verapamil** | Third-line | Use with caution | | **DC Cardioversion** | Unstable patients only | Safe | **Clinical Pearl:** The "best next step" in a stable SVT patient is always vagal maneuvers first, then adenosine — this is a classic NEET PG / board exam teaching point based on ACC/AHA/HRS 2015 SVT guidelines. [cite: ACC/AHA/HRS 2015 Guideline for SVT Management; Harrison's Principles of Internal Medicine, 21e, Ch. 235]