During congenital intracardiac surgery, excessive venous blood draining into the right atrium may indicate the presence of a/an:

The presence of excessive venous blood draining into the right atrium during congenital intracardiac surgery can indeed suggest the occurrence of a persistent left superior vena cava (SVC). This anatomical variation occurs when the left SVC remains present additional to the normal right SVC, which can lead to an increased volume of blood returning to the right atrium from the left side of the body.

In a normal scenario, venous blood from the upper body and head drains into the right atrium via the right SVC. However, if there is a persistent left SVC, the left upper extremity and part of the thoracic cavity can also contribute to blood flow directed towards the right atrium, resulting in a volume overload situation.

Conditions like patent ductus arteriosus, patent foramen ovale, or anomalous pulmonary venous return involve communication or connections between different circulatory pathways but do not primarily lead to excessive blood volume returning to the right atrium from the systemic venous return like a persistent left SVC does. In cases of the other options, the blood flow dynamics are predominantly altered during events like shunting rather than an increase in overall venous return to the right atrium itself.