Right-to-left anatomic shunt associated with a persistent left superior vena cava: the importance of injection site in demonstrating the shunt.

Anatomic right-to-left shunt causes hypoxemia that can pose a diagnostic challenge to clinicians. Among the many possible causes of right-to-left shunt, persistent left-sided superior vena cava (PLSVC) with an "unroofed" coronary sinus represents an uncommon congenital anomaly in which detection by saline-contrast echocardiogram (bubble echo) or contrast-enhanced CT scan requires injection of contrast in the left arm. We present the case of an elderly man with hypoxemia on the basis of a right-to-left shunt accompanying a PLSVC with unroofed coronary sinus in whom the shunt escaped initial detection following a bubble echo with contrast injected into the right arm. This case reminds pulmonary clinicians, who are frequently called on to assess the cause of hypoxemia, that specifying a contrast injection into the left arm is required in the pursuit of this specific shunt-producing anomaly.