Cardiac shunt

A cardiac shunt is a pattern of blood flow in the heart that deviates from the normal circuit of the

or both. The presence of a shunt may also affect left and/or right heart pressure either beneficially or detrimentally.

Terminology

The left and right sides of the

. A cardiac shunt is when blood follows a pattern that deviates from the systemic circulation, i.e., from the body to the right atrium, down to the right ventricle, to the lungs, from the lungs to the left atrium, down to the left ventricle and then out of the heart back to the systemic circulation.

A left-to-right shunt is when blood from the left side of the heart goes to the right side of the heart. This can occur either through a hole in the ventricular or atrial septum that divides the left and the right heart or through a hole in the walls of the arteries leaving the heart, called

in the left heart is higher than the right heart, which is the normal condition in birds and mammals.

Congenital shunts in humans

The most common

).

Acquired shunts in human

Biological

Some acquired shunts are modifications of congenital ones: a

may also be used to construct artificial passages.

Evaluation can be done during a

, 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 using the Flamm formula

${\displaystyle S_{v}O_{2}={\frac {3}{4}}\times SVC+{\frac {1}{4}}\times IVC}$

and Qp:Qs ratio

${\displaystyle Qp:Qs={\frac {\text{change in oxygen concentration across the pulmonary circulation}}{\text{change in oxygen concentration across the systemic circulation}}}={\frac {P_{V}-P_{A}}{S_{A}-S_{V}}}}$

where ${\displaystyle P_{V}}$ is the pulmonary vein, ${\displaystyle P_{A}}$ is the pulmonary artery, ${\displaystyle S_{A}}$ is the systemic arterial, and ${\displaystyle S_{V}}$ is the mixed-venous The Qp:Qs ratio is based upon the Fick principle and it is reduced to the above equation and eliminates the need to know cardiac output and hemoglobin concentration.

Mechanical

Mechanical shunts such as the

or blood pressure.

Reptile

All reptiles have the capacity for cardiac shunts.^[5]

References