Hyperpolarized ¹²⁹Xe Pulmonary MRI and Asymptomatic Atrial Septal Defect

In an asymptomatic 19-year-old who regularly underwent cardiopulmonary fitness testing for national lifeguard-accreditation, ¹²⁹Xe MRI unexpectedly revealed an abnormally augmented RBC signal and RBC-to-alveolar-capillary-tissue ratio with spatially homogeneous ventilation, tissue barrier, and RBC images. Pulmonary function was normal, but cardiopulmonary follow-up including transthoracic and transesophageal echocardiogram, heart catheterization, and contrast-enhanced cardiac CT imaging led to the diagnosis of a large (20 × 27 mm) secundum atrial septal defect (ASD) with a net right-to-left shunt (Qp:Qs = 0.5) and normal pulmonary pressures. This novel, unexpected case revealed that ¹²⁹Xe RBC signal intensity likely reflected erythrocytosis, compensatory to the abnormal cardiovascular hemodynamics that resulted from a large congenital ASD. Unlike ASD cases that present with dyspnea and exercise limitation, this ¹²⁹Xe MRI abnormality was detected in an asymptomatic teenager. This is the first report of asymptomatic adult congenital heart disease diagnosed subsequent to novel ¹²⁹Xe MRI that led to early intervention, avoiding long-term complications of cyanosis, including ventricular fibrosis and thromboembolic and bleeding risks.