In which of the following conditions left atrium is not enlarged -
Ans. is `b' i.e., ASD 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. All congenital hea diseases given in option cause left to right shunt. Size of left atrium in left to right shunts o In left to right shunt, blood enters from left side of hea (Lt. atrium, Lt ventricle or aoa) to right side of hea (Rt atrium, Rt ventricle or pulmonary aery) depending on the site of abnormal communication. o This blood then flows through pulmonary circulation and again enters the left atrium. o The path of blood is then depending on the defect. o In all these defects, left atrium recieves larger volume of blood which comes through pulmonary circulation --> Blood from right side of hea plus some blood from left side of hea because of shunt enter into pulmonary circulation and then into left atrium. So left atrium recieve blood volume larger than normal. o But the effect of larger volume on left atrium will be different in ASD and other left to right shunts. 1)In ASD Left atrium recieves extra volume of blood, but founate for the left atrium, it also has an extra exit for blood, i.e., septal defect. So, larger volume of blood is decompressed through left atrium. i) Amount, which is normally exits through AV valve (mitral valve) into left ventricle. ii) Extra amount, which left atrium recieves, exits through septal defect into right atrium. 2) Other left to right shunts (VSD, PDA, Aoopulmonary window). In these defects also, left atrium recieves extra volume of blood, But there is no extra exit. So, 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.
Ventricular septal defect
Atrial septal defect
Aoopulmonary window
Patent ductus aeriosus