Parasinusal Atrial Tachycardia Mimicking Inappropriate Sinus Tachycardia: Successful ECG-Guided Ablation without Three-Dimensional Mapping: A Case Report

Abstract

Background: Parasinusal atrial tachycardia (AT) is an uncommon form of focal supraventricular tachycardia that may closely mimic inappropriate sinus tachycardia (IST), creating diagnostic and therapeutic challenges. Differentiating these entities is crucial, as IST is primarily managed medically, whereas focal AT is amenable to curative ablation. Although three-dimensional (3D) electroanatomical mapping facilitates precise localization, it is not universally available, making surface electrocardiography (ECG) analysis essential. Case Summary: We report the case of a 54-year-old woman presenting with recurrent palpitations and dizziness. Initial ECG demonstrated a narrow-complex tachycardia with a ventricular rate of approximately 130 bpm. Detailed P-wave analysis revealed biphasic P waves in leads V1 and aVL, suggesting a right atrial origin. Electrophysiological study induced a parasinusal atrial tachycardia with earliest activation near the sinus node region, reproducing the patient’s symptoms. No evidence of accessory pathway or sinus node dysfunction was found. Despite beta-blocker therapy, symptoms persisted. Radiofrequency ablation was successfully performed using fluoroscopic guidance and ECG-based localization, without 3D mapping, resulting in complete arrhythmia suppression. Conclusion: This case highlights the diagnostic value of meticulous P-wave morphology analysis in distinguishing parasinusal AT from IST. Even in the absence of advanced mapping technologies, systematic ECG-guided localization can enable accurate diagnosis and effective curative ablation, particularly in resource-limited settings.