Bilateral Superior Venae Cavae With Crisscross Atrial Drainage.

To the Editor: We read with great interest the article by Tripathi and colleagues that reported the anomalous connection of the right superior vena cava (RSVC) to the left atrium (LA) and the left superior vena cava (LSVC) draining into the right atrium via the coronary sinus in a patient with sick sinus syndrome. It is an extremely rare anomaly. The authors diagnosed the patient as having an “RSVC draining into the LA and persistent LSVC (PLSVC) draining into the right atrium (RA) with symptomatic sinus node dysfunction.” The diagnosis is adequate judging from the hemodynamics. However, we consider that it is inappropriate as the anatomic diagnosis. Embryologically, the LSVC draining to the LA via the coronary sinus can be explained as the persistent left cardinal vein. However, the RSVC draining to the LA is incapable of being accounted for without some kind of defect. Actually, the computed tomography image showed that the RSVC connected not to the LA but to the right upper pulmonary vein. Therefore, the anatomic diagnosis of the patient is sinus venosus defect without (or with atretic) RSVC-RA connection and PLSVC. It is strange that the patient did not experience cyanosis. As the authors say, it could be explained by the existence of an azygos vein. The azygos vein usually exists distal to the sinus venous defect, and the computed tomography image proved the existence of the azygos vein. Therefore, the venous return from the right upper body could be partly drained to the inferior vena cava via the azygos vein. However, the azygos vein demonstrated on the computed tomography image is too narrow to drain the total RSVC blood flow. Thus, we surmise that the patient’s oxygen saturation was ≈90%. The authors did not mention oxygen saturation. We would like to know the oxygen saturation of the blood in the patient’s systemic artery (or the percutaneous oxygen saturation) and the pulmonary vein. Because the patient experienced sick sinus syndrome, we would like to know whether the patient was diagnosed as having heterotaxy syndrome or not, although the LSVC usually connects to the upper part of the left atrium in the patient with this syndrome.