This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': 'In which of the following conditions left atrium is not enlarged – \nSelect and explain. \nA. Ventricular septal defect, B. Atrial septal defect, C. Aortopulmonary window, D. Patent ductus arteriosus', 'role': 'user'}, {'content': 'Answer: B \nExplanation: ASD is associated with an enlarged right atrium & right ventricle to accommodate large volume of blood. The left atrium is not enlarged because it decompresses itself by shunting blood to the right atrium at a minor difference in pressure. The left atrium may enlarge once Eisenmenger’s syndrome develops and a reversal of shunt is seen across the defect.\nAll congenital heart diseases given in option cause left to right shunt.\nSize of left atrium in left to right shunts\n\nIn left to right shunt, blood enters from left side of heart (Lt. atrium, Lt ventricle or aorta) to right side of heart (Rt atrium, Rt ventricle or pulmonary artery) depending on the site of abnormal communication.\nThis blood then flows through pulmonary circulation and again enters the left atrium.\nThe path of blood is then depending on the defect.\nIn all these defects, left atrium recieves larger volume of blood which comes through pulmonary circulation → Blood from right side of heart plus some blood from left side of heart because of shunt enter into pulmonary circulation and then into left atrium. So left atrium recieve blood volume larger than normal.\nBut the effect of larger volume on left atrium will be different in ASD and other left to right shunts. 1)In ASD\nLeft atrium recieves extra volume of blood, but fortunate for the left atrium, it also has an extra exit for blood, i.e., septal defect.\nSo, larger volume of blood is decompressed through left atrium.\n\n\n\nAmount, which is normally exits through AV valve (mitral valve) into left ventricle.\nExtra amount, which left atrium recieves, exits through septal defect into right atrium. 2) Other left to right shunts (VSD, FDA, Aortopulmonary window).\n\n\nIn these defects also, left atrium recieves extra volume of blood, But there is no extra exit.\nSo, left atrium can pump out only normal amount of blood through mitral valve, and extra volume remains in the left atrium → Volume over load → Left atrial enlargement.', 'role': 'assistant'}]