Incidental Electrocardiographic Recognition of Left Anterior Fascicular Block With Delayed Troponin Elevation: A Case Report With Clinical Correlation.

Acute coronary syndrome (ACS) may present with initially nondiagnostic electrocardiographic findings and negative cardiac biomarkers, posing a diagnostic challenge and risk of delayed recognition. This is particularly relevant in cases involving coronary territories that are less well represented on standard ECG or in the setting of multivessel disease. We report the case of a 62-year-old man with hypertension who presented with typical chest pain of 2 hours' duration. Initial evaluation showed sinus rhythm with left axis deviation, consistent with likely left anterior fascicular block, without acute ST-segment elevation. High-sensitivity troponin measurements at 0, 1, and 3 hours were negative. Despite low-risk scores, the patient was admitted for observation due to persistent symptoms. Forty-eight hours later, he developed recurrent chest pain with a marked rise in troponin T and new inferolateral T-wave inversions, confirming evolving myocardial injury. Coronary angiography revealed significant stenosis of the right coronary artery and left circumflex artery, and successful percutaneous coronary intervention was performed. The patient had an uneventful recovery. This case highlights the limitations of early ECG and troponin-based assessment in ACS and underscores the importance of clinical judgment and serial reassessment, particularly in patients with persistent symptoms despite initially reassuring investigations.