144: EXTRINSIC COMPRESSION OF LAD BY UNDIAGNOSED METASTATIC COLON CANCER: A RARE CAUSE OF CARDIAC ARREST

Introduction: Acute coronary syndrome (ACS) and ST-elevation myocardial infarction (STEMI) are primarily caused by atherosclerotic coronary artery disease, plaque rupture, and thrombosis. However, 5% of ACS cases arise from non-atherosclerotic causes such as vasospasm, embolism, infections, or infiltrative diseases. Tumor-related coronary compression is exceedingly rare. We present a case of undiagnosed metastatic colon cancer that first presented as ACS. Description: A 69-year-old man with coronary artery disease (s/p stent), COPD, hypertension, and hyperlipidemia presented with two weeks of intermittent chest and abdominal pain. EKG showed diffuse ST elevations. Echocardiogram revealed a small pericardial effusion with preserved wall motion. Troponin peaked at 36 ng/mL. He remained hemodynamically stable, and pericarditis was suspected. CT chest showed cavitary lung nodules; abdominal CT revealed ascites without masses. On hospital day four, he developed hypotension, worsening chest pain, and lactic acidosis. Repeat EKG showed new anterolateral ST elevations. He was transferred to the ICU in shock and had cardiac arrest. Despite CPR and emergent pericardiocentesis, he could not be resuscitated. Autopsy revealed metastatic colon adenocarcinoma with peritoneal spread and pulmonary metastases. A tumor deposit on the anterior cardiac surface compressed the left anterior descending (LAD) artery, causing myocardial infarction. Discussion: Coronary compression from metastasis is an extremely rare etiology of STEMI. Most cardiac metastases involve the pericardium and are asymptomatic. In this case, the initial presentation mimicked pericarditis due to diffuse ST elevations and preserved function. The troponin elevation was mild. Rapid clinical deterioration and ST changes were the first true signs of ischemia. The final diagnosis was external LAD compression by metastatic colon cancer, identified only on autopsy. This case highlights the need to consider malignancy in an unexplained constellation of signs that involve multiple organ systems, even in the absence of cancer history. In our case, diagnostic tests were inconclusive of a unifying etiology. Such atypical scenarios require consideration of broad differential diagnoses, early advanced imaging (MRI/ PET) and tissue sampling for a timely diagnosis.