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My name is David Bailly. I am a fellow here at Boston Children’s Hospital in the Department of Anesthesia and Critical Care. I am also a boarded Pediatrician and a boarded Pediatric Cardiologist. And I’m going to speak with you today about atrial septal defects. Atrial septal defects are very common overall and they’re common seen with other cardiac lesions. Up to 50% of all cardiac constellations include an atrial septal defect.] We’re going to talk initially about the anatomy and the physiology of the different types of atrial septal defects, followed by the usual presentations, including some of the unusual presentations, followed by the imaging and diagnostic modalities used to help us treat and diagnose atrial septal defects, followed by initial management strategies for patients with atrial septal defects and the sequel of that lesion.
Anatomy and Physiology.
So we’ll start out with the anatomy and physiology. Atrial septal defects are simply and defect in the atrial septum; they can be large, they can be small, they can be single, there can be many defects anywhere within the atrial septum. The three broad categories that we typically divide them out into are secundum atrial septal defects, which account for about 70% of the defects we see, and those are actually a defect in the primum portion of the septum from an embryologic standpoint. The second most common type is primum defects, which are defects in the atrial septum that occur in the inferior level of the atrial septum. They’re often associated with AV canal defects, but they don’t always have to be. The last type are the sinus venosus atrial septal defects, and they broadly fan out into two categories: those involving the superior vena cava, which are the most common type, and those involving the inferior vena cava, which are the least common type. Those are essentially a defect in the lumen of the SVC and the lumen of a pulmonary vein, so it’s just that there a communication. The entrance to the pulmonary veins is actually normal back into the left atrium, but because there’s a communication between the wall of the pulmonary vein and the wall of the superior vena cava, a left to right shunt occurs. So the physiology of all atrial septal defects is essentially a left to right shunt at the atrial level that evokes a volume burden on the right side of the heart. And we can use box diagrams to illustrate this quite clearly.
The box diagram here shows that we have the right atrium, the right ventricle, into the pulmonary arteries, the blood will return to the left side of the heart in to the left atrium, the left ventricle, and into the aorta. So if we draw blood flowing through the heart in the usual pathway, you’ll see, denoted here as simply an arrow, blood going to the RA, the RV, the PAs, and then back to the left side of the heart. This is the usual course of blood flow, as you all know. Now, if there is an atrial septal defect, once the blood returns to the left atrium, it essentially has a decision to make. Is it going to shunt to the right side of the heart or continue on to the left side of the heart?
The definitive point of where the blood shunts is determined by the relative compliance of the two ventricles. Now, at birth, the right ventricle is less compliant because it has essentially been behaving as a left ventricle in utero by providing systemic circulation through the ductus arteriosus. However, after birth, the placenta is detached, the lungs are inflated, the pulmonary vascular resistance drops, and the systemic vascular resistance rises over time, as the LV supports the systemic circulation. And as we go through life and have coronary artery disease and other reasons to have hypertension, the LV becomes less compliant, the RV becomes more compliant.