What is meant by single ventricle physiology and how is it identified prenatally?

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Single ventricle physiology means one ventricle is responsible for pumping blood to both the systemic and pulmonary circulations. In this situation there is not a clearly separated left and right ventricle, so the circulations run in parallel rather than in the normal serial fashion. Prenatally, this is identified with fetal echocardiography by finding a single dominant ventricular chamber receiving inflow from both atria (often via a common AV valve or a severely hypoplastic second ventricle) and by abnormal or absent outflow tract patterns. Color Doppler can show the aorta and pulmonary artery arising in a way that suggests parallel paths from the single ventricle, with mixing of blood at the atrial or ventricular level.

The other descriptions describe normal anatomy or a specific condition that is not the general definition. Two normal ventricles with separate circulations and a normal heart with two outflow tracts are not single ventricle physiology. Isolated left heart hypoplasia is a specific form that can lead to single ventricle physiology, but it is not the broad definition being tested.