Unidentified Flying Objects: An Infected Left Atrial Appendage Thrombus as a Nidus for Persistent Methicillin-Resistant Staphylococcus aureus Bacteremia

Infections of intracardiac thrombi are exceptionally rare but pose significant clinical risks, especially when located in the left atrial appendage (LAA). We present a unique case of a 51-year-old male with multiple comorbidities who was found to have an infected LAA thrombus causing persistent methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) bacteremia and systemic symptoms. Initial presentation included altered mental status, diabetic ketoacidosis, and classic signs of endocarditis such as splinter hemorrhages. Transesophageal echocardiogram imaging revealed a thrombus in the LAA, which was later confirmed to be infected and was acting as a nidus for sepsis. Surgical intervention and targeted antibiotic therapy led to clinical improvement. This case highlights the need for heightened clinical suspicion and a multidisciplinary approach when managing unexplained bacteremia, particularly in patients with known thrombotic risk factors. It also underscores the rare but significant potential for cardiac thrombi to become secondarily infected, warranting further study into diagnostic and therapeutic strategies.