A 55-year-old woman has recurrent paroxysmal supraventricular tachycardia (PSVT). ECG during an episode shows narrow QRS tachycardia at 180 bpm with retrograde P waves within the QRS. What is the mechanism and long-term ablation target?

• A AVRT (orthodromic) via accessory pathway — ablate the accessory pathway
• B Atrial flutter — ablate the cavotricuspid isthmus
• C Focal atrial tachycardia — locate and ablate the ectopic focus
• D AVNRT (typical slow-fast) — ablate the slow pathway of the AV node ✓

Explanation

Retrograde P waves buried in or immediately at the end of QRS (RP < 80 ms, P seen as a pseudo-R' in V1 or pseudo-S in inferior leads) is characteristic of typical AVNRT (slow-fast), where antegrade conduction is via the slow AV nodal pathway and retrograde conduction is rapid via the fast pathway. Catheter ablation targets the slow pathway of the AV node (posteroseptal region near the coronary sinus ostium) with > 95% success rate. In AVRT (WPW), retrograde P waves are after the QRS (RP interval ≥ 80 ms) and the accessory pathway itself is ablated.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.