INFECTIVE ENDOCARDITIS OF THE MITRAL VALVE COMPLICATED BY PLATYPNEA-ORTHODEOXIA SYNDROME IN AN ADULT WITH ATRIAL SEPTAL DEFECT AND BIDIRECTIONAL SHUNTING

Case Presentation: BackgroundAtrial septal defect (ASD) accounts for 20–40% of congenital heart disease in adults. Since intracardiac shunt velocity is typically low, the risk of infective endocarditis (IE) is considered minimal. However, rare cases of IE have been reported in patients with right-to-left or bidirectional shunting, which may allow septic emboli to bypass the pulmonary circulation.Case PresentationA 48-year-old man with a childhood history of ASD presented with progressive musculoskeletal pain and worsening dyspnea. Twenty-one days before admission, he developed left shoulder and low-back pain that progressed to severe difficulty with movement, prompting emergency transport to our hospital. On arrival, he was alert with a Glasgow Coma Scale score of E4V3M6, blood pressure of 126/88 mmHg, heart rate of 120 bpm, oxygen saturation of 91% on 5 L/min supplemental oxygen, and a systolic murmur. Digital clubbing and Osler’s nodes were noted. Laboratory findings revealed marked inflammatory response, acute kidney injury, and elevated NT-proBNP level. Transthoracic echocardiography revealed a 10-mm vegetation on the anterior leaflet of the mitral valve. Computed tomography revealed cerebral high-density lesions, cavitary pulmonary nodules, and splenic and renal infarcts. Blood cultures identified methicillin-sensitive Staphylococcus aureus (MSSA), leading to a diagnosis of mitral valve IE with multiple septic emboli. Ampicillin/Sulbactam at 12 g/day was initiated.During hospitalization, the patient developed severe hypoxemia when moved to a semi-upright position. Transesophageal echocardiography revealed ASD with bidirectional shunting. Given the pulmonary findings, hypoxemia was attributed to Platypnea–Orthodeoxia Syndrome (POS) related to right-to-left shunting. His condition gradually improved with antimicrobial therapy and respiratory support. An elective ASD closure was planned, and he was transferred to a rehabilitation hospital on hospital day 44.

Discussion: DiscussionThis case highlights that patients with ASD and a right-to-left or bidirectional shunt may have a higher risk of systemic IE due to septic material entering the systemic circulation. The concomitant POS reflected a substantial hemodynamic consequence of the shunt. In addition, pulmonary lesions typical of right-sided IE raise the possibility of concurrent septic embolization to both the pulmonary and systemic circulations.

Conclusions: ConclusionAlthough IE is uncommon in ASD with low shunt velocity, progression to bidirectional shunting can predispose to systemic IE. Clinicians should consider IE when ASD patients present with fever or embolic manifestations.