How is a dominant ventricle identified in single-ventricle physiology?

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In single-ventricle physiology, the dominant ventricle is identified by which ventricle appears larger on the four-chamber view. The larger ventricle is the one bearing the greater workload and thus becomes the dominant, systemic ventricle. This size relationship is a direct, practical clue visible in a single image plane that compares both ventricles side by side, making it a reliable way to define dominance during prenatal assessment.

Other criteria are less reliable in this scenario. Simply noting which ventricle pumps to the pulmonary artery doesn’t reliably establish dominance, because the outflow connections can vary in univentricular hearts. Determining dominance by which ventricle pumps systemically would be circular if dominance hasn’t been established yet. And the mere presence of a single ventricle on imaging doesn’t always reflect functional dominance, since two ventricles can be present with one acting as the dominant, systemic ventricle.