Atypical ECG in AVNRT: Teaching Points from a Common Tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common form of regular supraventricular tachycardia, typically characterized by retrograde P waves that are negative or absent in the inferior leads. We report a case of a 63-year-old man presenting with recurrent palpitations and documented narrow QRS tachycardia. Surface electrocardiogram during tachycardia revealed an atypical finding: positive P waves in the inferior leads, suggestive of atrial tachycardia. Comprehensive electrophysiological study demonstrated dual AV nodal physiology, induction of short RP tachycardia, and a VAV response to ventricular entrainment, confirming the diagnosis of typical (slow-fast) AVNRT. Detailed mapping identified an altered atrial activation sequence, accounting for the unusual P wave polarity. The patient underwent successful slow pathway ablation with complete resolution of symptoms. This case underscores the importance of recognizing that typical AVNRT can occasionally present with unexpected P wave morphology, potentially mimicking other arrhythmias. Accurate interpretation of surface ECG findings, combined with systematic electrophysiological evaluation, is essential to avoid misdiagnosis and ensure appropriate management. Electrophysiologists should be aware of such atypical presentations to optimize diagnostic accuracy and therapeutic outcomes in patients with supraventricular tachycardia.