Svt mimicry in fascicular vt: Importance of early recognition and class i ablation strategy

Abstract Background Idiopathic left fascicular ventricular tachycardia (ILFVT) is a form of ventricular tachycardia characterized by a relatively narrow QRS complex, frequently mimicking supraventricular tachycardia. Differentiating VT from SVT remains challenging despite available electrocardiography (ECG) algorithms but is essential due to differing mechanisms and treatment strategies, as misdiagnosis may result in inappropriate and potentially harmful management. Case Illustration A 42-year-old male presented with recurrent palpitations since 2021, predominantly during exertion and relieved by rest. Symptoms worsened in late 2024 and were refractory to medical therapy, including verapamil. The patient had a history of coronary artery disease with prior percutaneous coronary intervention to the proximal-mid left anterior descending artery in 2025. Physical examination and baseline electrocardiogram during sinus rhythm were unremarkable. Holter monitoring showed rare premature ventricular and atrial complexes without sustained arrhythmia. Transthoracic echocardiography demonstrated preserved left ventricular systolic function (ejection fraction 64%) with regional wall motion abnormalities consistent with prior LAD ischemia. During electrophysiological study, non-sustained ventricular tachycardia was inducible, showing right bundle branch block morphology with superior axis, suggestive of posterior fascicular ILVT. Mapping identified Purkinje potential at the inferoapical left ventricle. Radiofrequency ablation was successfully performed, and post-procedure arrhythmia was no longer inducible. The patient remained asymptomatic at follow-up. Conclusion This case highlights the importance of distinguishing fascicular VT from SVT mimics. Early electrophysiological evaluation enables accurate diagnosis and definitive treatment, while catheter ablation targeting Purkinje potentials provides a safe and effective Class I strategy.Figure 1.ECG Idiopathic left fascicular ventricular tachycardia