How Do the Heart and Lungs Work?
To understand intracardiac shunts, it is important to understand normal cardiac anatomy and physiology. The heart is divided into two sides, left and right. The right side receives venous (low oxygen) blood returning from the rest of the body. The blood is pumped to the lungs to be re-oxygenated. Blood flowing through the lungs is exposed to oxygen from breathing and is returned to the left side of the heart as high oxygen blood. The blood is pumped though arteries to the body.
What Is Intracardiac Shunting?
Intracardiac shunting occurs when cardiac blood flow takes a shortcut within the heart. This is the result of a hole in the walls that normally separate arterial (high oxygen) from venous (low oxygen) blood. This shortcut allows the mixing of arterial and venous blood without the normal pathway being used to re-oxygenate blood through the lungs. This mixing of blood can lead to low oxygen levels or decompression illness (the bends from scuba diving). These holes in the walls are sometimes associated with strokes. More rarely, this can lead to heart rhythm problems, heart failure, and pulmonary hypertension.
Most often, these holes exist within the wall of the heart that divides the top chambers of the heart (atria), called the interatrial septum. Less frequently, these holes exist within the lower part of the septum, called the interventricular septum. Defects in the interatrial septum include patent foramen ovale (PFO) and atrial septal defect (ASD). In the lower heart, they are called ventricular septal defects (VSD).
Do All of Us Have Holes in Our Hearts?
All of us have a PFO early in our development. In fact, PFOs are necessary to support our circulation in fetal life.
However, shortly after birth, PFOs close spontaneously in about 70 percent of people. While about 30 percent of the population has a residual PFO after birth, only a small percentage will ever require treatment. In contrast, ASDs are relatively rare, occurring in less than 1 percent of the population.