A 72-year-old woman from Mumbai is admitted with palpitations and dyspnea. Her ECG shows a regular narrow-complex tachycardia at 160 bpm with a PR interval of 0.08 seconds (short PR) and a slurred upstroke (delta wave) in the QRS complex. She is hemodynamically stable. What is the most appropriate immediate next step in management?

Question

Accepted Answer

D. Administer intravenous adenosine 6 mg rapid push followed by saline flush. ## ECG Diagnosis: Wolff-Parkinson-White (WPW) Syndrome with Atrioventricular Reentrant Tachycardia (AVNRT) **Key Point:** The **short PR interval (<0.12 s)** and **delta wave** (slurred QRS upstroke) are pathognomonic for **pre-excitation** via an **accessory pathway (AP)**. In the setting of a regular narrow-complex tachycardia, this is **AVNRT in WPW syndrome**. **High-Yield:** WPW-associated AVNRT is the most common tachyarrhythmia in patients with pre-excitation. The reentry circuit uses the AV node (orthodromic) and the AP (antidromic) in a reciprocal loop. ## Acute Management of Hemodynamically Stable AVNRT in WPW ### First-Line Agent: Adenosine **Mechanism:** Adenosine blocks AV nodal conduction, breaking the reentry circuit by interrupting the orthodromic limb of the circuit. **Dosing:** - Initial: **6 mg IV rapid push** followed by 10–20 mL saline flush - If no response in 1–2 minutes: **12 mg IV rapid push** - Success rate: >90% for AVNRT termination **Clinical Pearl:** Adenosine works **rapidly** (within seconds) and is **safe** even in the elderly because its half-life is <10 seconds. Transient asystole or brief hypotension is expected and self-limited. **Warning:** ~~Verapamil~~ is **contraindicated in pre-excited atrial fibrillation** (AF with WPW) because it blocks the AV node preferentially, forcing conduction down the AP, which may have a shorter refractory period and cause rapid ventricular rates or degeneration to VF. However, in **orthodromic AVNRT** (narrow-complex), verapamil is theoretically safe but is **second-line** because adenosine is faster and more reliable. ```mermaid flowchart TD A["Regular narrow-complex tachycardia
+ short PR + delta wave"]:::outcome --> B{"Hemodynamically stable?"}:::decision B -->|Yes| C["Adenosine 6 mg IV push"]:::action C --> D{"Tachycardia terminated?"}:::decision D -->|Yes| E["Diagnosis: AVNRT in WPW
Arrange EP study for ablation"]:::outcome D -->|No| F["Adenosine 12 mg IV push"]:::action F --> G{"Terminated?"}:::decision G -->|Yes| E G -->|No| H["Consider verapamil or diltiazem"]:::action B -->|No| I["Synchronized DC cardioversion"]:::urgent ``` ## Why Other Options Are Suboptimal | Option | Reason | |--------|--------| | **DC Cardioversion** | Reserved for hemodynamic instability or adenosine failure. This patient is stable and adenosine is first-line. | | **Verapamil** | Second-line agent; slower onset than adenosine. Also carries risk in pre-excited AF (though not relevant here). | | **EP Study** | Diagnostic and therapeutic (ablation) but NOT an acute management step. EP study is arranged **after** acute termination and stabilization. | **High-Yield:** The **short PR interval persists** even when the tachycardia is terminated (it is a baseline feature of WPW). Do not mistake resolution of tachycardia for resolution of pre-excitation; the AP remains and requires definitive ablation. ## Definitive Management After acute termination: 1. **Electrophysiology study** to localize the AP 2. **Radiofrequency catheter ablation** of the AP (curative; >95% success) 3. Avoid long-term rate-limiting drugs (beta-blockers, verapamil) in pre-excited AF because they increase AP conduction risk ![ECG — Waves and Intervals diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/3697.webp)

Answer

A. Perform synchronized DC cardioversion under sedation

Answer

B. Start oral verapamil 80 mg and observe for response

Answer

C. Obtain an electrophysiology study to confirm the diagnosis and plan ablation

Explanation

ECG Diagnosis: Wolff-Parkinson-White (WPW) Syndrome with Atrioventricular Reentrant Tachycardia (AVNRT)

Acute Management of Hemodynamically Stable AVNRT in WPW

First-Line Agent: Adenosine

Why Other Options Are Suboptimal

Definitive Management

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Option	Reason
DC Cardioversion	Reserved for hemodynamic instability or adenosine failure. This patient is stable and adenosine is first-line.
Verapamil	Second-line agent; slower onset than adenosine. Also carries risk in pre-excited AF (though not relevant here).
EP Study	Diagnostic and therapeutic (ablation) but NOT an acute management step. EP study is arranged after acute termination and stabilization.