Large Mitral Valve Infective Endocarditis Missed on Initial Transthoracic Echocardiography in a Patient With Severe Aortic Stenosis and Complex Multisystem Comorbidities

Infective endocarditis is a life-threatening condition requiring early diagnosis and prompt management. Transthoracic echocardiography (TTE) is commonly used as an initial diagnostic tool; however, its sensitivity may be limited in patients with complex structural heart disease. We report a 57-year-old male with severe calcific aortic stenosis and multiple comorbidities who presented with persistent Staphylococcus aureus bacteremia. Initial TTE showed no evidence of vegetations despite high clinical suspicion. Due to ongoing clinical deterioration, transesophageal echocardiography (TEE), performed 20 days later, revealed large mitral valve vegetations measuring up to 22 × 12 mm, associated with progression to severe mitral regurgitation. This case highlights the limitations of TTE in high-risk patients and emphasizes the importance of early TEE, particularly in the presence of persistent bacteremia and clinical deterioration, to avoid delayed diagnosis and adverse outcomes.