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Congenital Cardiac Left to Right Shunts
Healthy Heart
Typically, post-natal systemic and pulmonary circulation run in parallel and maintain separation between low and high oxygen blood. When separation is incomplete, low and high oxygen blood mix, which produces systemic blood with insufficient oxygen concentrations.
Review fetal circulation & adult circulation
The Great Vessels
- The aorta carries blood with a high oxygen concentration to the body tissues.
- The pulmonary trunk carries blood with a low oxygen concentration to the lungs.
- Ductus arteriosus
- Allows blood to flow from pulmonary trunk to aorta, bypassing the lungs.
- The ligamentum arteriosus is the adult remnant of the ductus arteriosus.
Ventricular septal defects
Characterized by an incomplete ventricular septum, which allows oxygenated blood to pass from the left ventricle to the right, which then returns it to the lungs.
Atrial septal defects
Allow oxygenated blood from the left atrium to pass into the right heart and, ultimately, back through the pulmonary circulation.
Patent ductus arteriosus
Typically, the ductus arteriosus regresses after birth and becomes the ligamentum arteriosus; however, in some cases, the channel persists.
- Low pulmonary vascular pressure allows oxygenated blood to "backflow" from the aorta into the pulmonary trunk, which then recirculates it through the lungs.
Eisenmenger syndrome
Occurs when an uncorrected congenital left to right shunt induces anatomical changes that reverse the shunt.
- A congenital left to right shunt increases pulmonary blood flow.
- Increased pulmonary blood flow work induces hypertrophy of the right ventricle.
- Hypertrophic right ventricle becomes so powerful that it eventually overwhelms the pressure from the left ventricle and sends deoxygenated blood directly into the left ventricle, causing hypoxemia.