Editing Cardiac catheterization (section)

===Shunt evaluation===
[[File:Atrial septal defect-en.png|thumb|Atrial septal defect with left-to-right shunt]]

[[Cardiac shunt]]s can be evaluated through catheterization. Using oxygen as a marker, the [[oxygen saturation]] of blood can be sampled at various locations in and around the heart. For example, a left-to-right [[atrial septal defect]] will show a marked increase in oxygen saturation in the right atrium, ventricle, and pulmonary artery as compared to the [[mixed venous oxygen saturation]] from the oxygenated blood from the lungs mixing into the venous return to the heart. Utilizing the [[Fick principle]], the ratio of blood flow in the lungs (Qp) and system circulations (Qs) can calculate the Qp:Qs ratio. Elevation of the Qp:Qs ratio above 1.5 to 2.0 suggests that there is a hemodynamically significant left-to-right shunt (such that the blood flow through the lungs is 1.5 to 2.0 times more than the systemic circulation). This ratio can be evaluated non-invasively with [[echocardiography]] too, however.{{citation needed|date=March 2021}}

A "shunt run" is often done when evaluating for a shunt by taking blood samples from [[superior vena cava]] (SVC), [[inferior vena cava]] (IVC), [[right atrium]], [[right ventricle]], [[pulmonary artery]], and system arterial. Abrupt increases in oxygen saturation support a left-to-right shunt and lower than normal systemic arterial oxygen saturation supports a right-to-left shunt. Samples from the SVC & IVC are used to calculate [[mixed venous oxygen saturation]].{{citation needed|date=March 2021}}
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