ATRIAL SEPTAL DEFECT



Atrial septal defects are classified according to their location in the atrial septum. Ostium secun­dum defects are in the region of the fossa ovalis, ostium primum in the low atrial septum, and sinus venosus in the upper septum near the junc­tion of the vena cava and the right atrium. Ostium primum atrial septal defects are often associated with other endocardial cushion developmental defects, such as a cleft mitral valve or ventricular septal defect. Sinus venosus defects are almost al­ways associated with partial anomolous pulmo­nary venous return (a pulmonary vein enters the right atrium or vena cava instead of the left atrium, adding to the left-to-right shunt).
In most atrial septal defects, the pressure equili­brates between the left and the right atrium, and the degree of left-to-right shunt depends not on a pressure gradient but instead on the relative com­pliance of the right ventricle and pulmonary ar­terial system compared to the left ventricle and systemic arterial system. Pulmonary vascular re­sistance and pulmonary arterial pressure tend to remain low, and thus pulmonary hypertension and right-to-left shunt (Eisenmenger’s syndrome) do not occur commonly.
Atrial septal defects may go undetected in chil­dren because there are minimal or no symptoms and the ejection murmur across the pulmonic valve is thought to be functional. Survival into adulthood is expected but longevity is shortened, and death is usually due to cardiac failure. Oc­casionally, a young adult develops pulmonary hy­pertension. In addition to findings of congestive heart failure, atrial tachyarrhythmias become more frequent in patients over age 40 and may be the presenting symptom.
Patients with atrial septal defects generally ap­pear normal. However, patients with the Holt-Oram syndrome have upper extremity skeletal ab­normalities- with a secundum defect, and patients with Down’s syndrome have the typical features of mongolism and often a primum defect. The murmur is generated by the increased stroke vol­ume flowing into a dilated pulmonary trunk; a murmur across the atrial septal defect is rare. Echo­cardiography reveals the dilated right ventricle and abnormal motion of the interventricular sep-ocardiography reveals the dilated right ventricle and abnormal motion of the interventricular sep­tum; these findings are referred to as “right ven­tricular volume overload” and are also present in pulmonic regurgitation, tricuspid regurgitation, and Ebstein’s anomaly. Ostium primum defects and many ostium secundum defects can be vis­ualized directly with two-dimensional echocar­diography or indirectly after peripheral venous injection of echocardiographic contrast. However, cardiac catheterization may be required to deter­mine the degree of shunt and evaluate for asso­ciated defects. Patients who have uncomplicated atrial septal defects without pulmonary hyperten­sion and shunt ratios exceeding 1.5 should undergo repair electively, preferably during childhood.





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