Introduction: A coronary sinus atrial septal defect, also known as an unroofed coronary sinus (UCS), is an exceedingly rare congenital anomaly with rates of less than 1% of all atrial septal defects. This defect often presents with left to right shunting and may be misdiagnosed as idiopathic pulmonary arterial hypertension (PAH) leading to right heart failure. Description: A 75 year-old female with diagnosed with idiopathic PAH presented for evaluation of dyspnea, lower extremity edema, and signs of right heart failure which was confirmed on initial workup. Subsequent transthoracic echocardiography demonstrated a severely dilated right atrium, right ventricle (RV), and left atrium with severely reduced RV systolic function and preserved left ventricular function. CT was reviewed again which revealed a possible UCS and this was confirmed on cardiac MRI as a 1.8cm wide coronary sinus atrial septal defect with no evidence of persistent left superior vena cava. This is known as a type II UCS. She underwent a right heart catheterization which showed left to right shunting with an oxygen step-up from 68% to 90.6% in the RA and a calculated shunt ratio of 2.2 and Qp/Qs of 2.4. The patient’s symptoms improved with diuresis, and she was referred for surgical correction. Discussion: This case highlights the challenge posed by rare congenital defects in adults presenting with unexplained PAH or acute right heart failure. The delayed recognition and absence of a persistent left superior vena cava further illustrates the need for multimodal imaging and reasonable clinical suspicion. Early identification and repair may improve symptoms and percent long term complications such as paradoxical emboli and progressive RV failure.
Fowajuh et al. (2026) studied this question.