A Rare Case of Chronic Thromboembolic Pulmonary Hypertension in an Elderly With Atrial Septal Defect and Eisenmenger Syndrome.

Atrial septal defects (ASDs) are among the most common congenital heart anomalies and often remain undetected until adulthood. While small ASDs may close spontaneously, larger unrepaired defects can lead to serious complications such as right heart failure, pulmonary arterial hypertension, Eisenmenger syndrome (ES), and thromboembolic events. We present a case of a 66-year-old Filipino female with a longstanding unrepaired secundum-type ASD, who was admitted with progressive dyspnea and hypoxemia. The patient developed atrial flutter, and further workup revealed severe pulmonary hypertension, right ventricular failure, and pulmonary embolism. Imaging confirmed chronic thromboembolic pulmonary hypertension (CTEPH), a rare but life-threatening complication in patients with ES. Despite aggressive medical management, including anticoagulation, antibiotics for pneumonia, and antiarrhythmic therapy, the patient's condition deteriorated, and she eventually succumbed to her illness. This case highlights the critical importance of early detection and surgical repair of large ASDs to prevent irreversible pulmonary vascular disease and associated complications such as ES and CTEPH, particularly in resource-limited settings where definitive interventions are often inaccessible.