A 58-year-old man from Delhi presents to the emergency department with sudden-onset palpitations and syncope. ECG shows a regular narrow-complex tachycardia at 180 bpm with retrograde P waves visible in the ST segment. He has no structural heart disease on echocardiography. Adenosine IV bolus terminates the arrhythmia. What is the most appropriate next step in management?

Explanation

## Clinical Diagnosis **Key Point:** The clinical presentation — regular narrow-complex tachycardia with retrograde P waves in the ST segment, adenosine-responsive, and no structural heart disease — is pathognomonic for **atrioventricular reentrant tachycardia (AVRT)** due to an **accessory pathway** (Wolff-Parkinson-White syndrome or concealed pathway). ## Mechanism of AVRT AVRT occurs when an **accessory pathway** (bypass tract) outside the AV node provides an alternative route for conduction. The reentrant circuit typically involves: 1. Antegrade conduction via the normal AV node 2. Retrograde conduction via the accessory pathway 3. This produces retrograde P waves (inverted, buried in or immediately after the QRS or in the ST segment) ## Why Adenosine Works **High-Yield:** Adenosine blocks the AV node (slows conduction through the normal pathway), which breaks the reentrant circuit and terminates AVRT. This adenosine responsiveness is diagnostic. ## Next Step: Definitive Management **Clinical Pearl:** Once AVRT is diagnosed, the patient has experienced a **symptomatic arrhythmia with syncope** — a high-risk feature. The definitive and curative treatment is **electrophysiological study (EPS) with radiofrequency ablation (RFA)** of the accessory pathway. - **EPS** allows precise localization of the pathway - **RFA** ablates the pathway with >95% success rate and low recurrence - This is curative and eliminates the need for lifelong antiarrhythmic therapy - Indicated in symptomatic patients, especially those with syncope or hemodynamic compromise ## Why Other Options Are Suboptimal | Option | Why Not Correct | |--------|----------------| | Beta-blocker monotherapy | Addresses symptoms only; does not cure the underlying accessory pathway. Patient remains at risk for recurrent arrhythmias and syncope. Not definitive. | | Repeat adenosine challenge | Adenosine was already diagnostic and therapeutic. Repeating it adds no new information and delays definitive treatment. | | Coronary angiography | No clinical indication. Echo already ruled out structural disease. CAD is not the cause of AVRT. | **Mnemonic:** **AVRT = Accessory pathway + Reentrant circuit → EPS + RFA = Cure**