APCU25MPA5 The imposter beside the heart: extra – cardiac mass mimicking acute coronary syndrome

Introduction Chest pain in the emergency room often sets off alarms for acute coronary syndrome (ACS). The ECG is printed, the troponins are drawn, and treatment is often rushed. Yet sometimes the heart is not the real culprit. Rarely, a lesion lying just outside the heart can create the same fear and mimic the same signs. This case describes one such masquerader.Case Presentation A 47-year-old woman with dyslipidemia came to the hospital with two days of chest pain radiating to her shoulder and back. The pain was moderate, a steady 5/10, and unlike the classic textbook angina she had no sweating or breathlessness. Her vitals were stable except for a widened pulse pressure (BP 160/50 mmHg). On examination, nothing dramatic was found. But her ECG raised eyebrows: sinus rhythm with a Q wave in lead III, an ominous marker for inferior ischemia. The suspicion for ACS was strong. Yet, bedside echocardiography told a different story. A bright shadow appeared near the right ventricle; a mass where none should be. A formal echo confirmed good heart function (LVEF 60%, TAPSE 2.4 cm) but raised the same concern: this was not inside the heart, but pressing from outside. HRCT thorax solved the puzzle; a cystic lesion, 5 × 2.5 × 4.9 cm, sitting beside the right atrium. CT coronary angiography, finally, cleared the coronaries of any disease.Discussion This case demonstrates how an extra-cardiac mass can mimic ACS through compressive effects on the right heart. The patient’s chest pain and Q wave in lead III suggested inferior ischemia, but multimodality imaging identified the true culprit: a cystic lesion exerting external pressure. Similar cases of pericardial and mediastinal cysts have been described, where extrinsic compression leads to angina-like symptoms without coronary obstruction. Distinguishing such mimics is crucial, as treatment strategies differ entirely—management may involve surveillance or surgical excision, whereas misdiagnosis as ACS could lead to inappropriate antiplatelet or invasive therapies.Conclusion Extra-cardiac masses can simulate ACS by compressing cardiac chambers or adjacent structures, producing ischemia-like chest pain and misleading ECG changes. In patients with atypical features or persistent symptoms despite normal coronaries, clinicians must consider external cardiac compression as a differential. Vigilant use of multimodality imaging ensures accurate diagnosis and prevents unnecessary interventions.