A case of atrial septal defect with right-to-left shunting without pulmonary hypertension

We report a case of a 54-year-old man with atrial septal defect who presented with oxygen desaturation on pulse oximetry. Cardiac magnetic resonance imaging and transesophageal echocardiography showed right-to-left shunting through an atrial septal defect, which was confirmed by superior vena cavography and suggested Eisenmenger syndrome. However, cardiac catheterization revealed a normal pulmonary arterial pressure. Simultaneous measurement of interatrial pressure identified two transient interatrial pressure gradient points, where the right atrial pressure was higher than the left atrial pressure. The patient was finally diagnosed with atrial septal defect without pulmonary hypertension. Right-to-left shunting was primarily caused by a transient interatrial pressure gradient due to a time delay in both initial atrial contraction and completion of passive ventricular filling between the right and left sides of the heart. Surgical closure of the atrial septal defect was performed, and hypoxemia improved. This is the first report of right-to-left shunting without pulmonary hypertension caused by a transient interatrial pressure gradient due to a time delay between the right and left cardiac cycles. Precise assessment of the simultaneous interatrial pressure in addition to diagnostic imaging played a pivotal role in clarifying the etiology of this rare condition.

Atrial septal defect with right-to-left shunting without Eisenmenger syndrome is a rare condition. We identified transient interatrial pressure gradients associated with a time delay in both initial atrial contraction and completion of the passive ventricular filling phase, which we considered as the primary mechanism underpinning right-to-left shunting. Simultaneous measurement of interatrial pressure played a pivotal role in elucidating the hemodynamics and abnormal shunt flow mechanism.