Atrial septal defect - Secundum
An atrial septal defect of the secundum type is relatively common and occurs from failure of the septum secundum to develop. This results in a communication between the left and right atrium directly causing a left to right shunt. Over time, pulmonary hypertension can develop causing right heart enlargement and eventual pulmonary hypertension. When this pulmonary hypertension is severe enough, the direction of shunt reverses to right to left causing Eisenmenger’s syndrome.
Diagnosis is made on transthoracic echocardiography. The 12-lead ECG will show an incomplete right bundle branch block with right axis deviation (in contrast to the priumum ASD which has a left axis deviation).
The image to the right shows the location of the different types of atrial septal defects while looking from the right atrium.
1 = Upper sinus venosus defect
2 = Lower sinus venosus defect
3 = Ostium secundum atrial septal defect
4 = Coronary sinus atrial septal defect
5 = Ostium Primum atrial septal defect
The murmur produced by an ASD is due to increased flow through the pulmonic valve, thus it is remarkably similar to that of pulmonic stenosis. The difference lies in the intensity and splitting pattern of the S2 heart sound. The intensity of S2 should remain unchanged and may infact be accentuated if pulmonary hypertension develops. The S2 is fixed-split in a person with an ASD. This differs from the widened split S2 seen in severe pulmonic stenosis. Also, the murmur of an ASD does not increase in intensity with inspiration like that of pulmonic stenosis.
A secundum atrial septal defect is diagnosed on transthoracic echocardiography. The 12-lead ECG will show an incomplete right bundle branch block and right axis deviation (in contrast to the primum ASD which has a left axis deviation).
Closure of an atrial septal defect can be done either percutaneously with a closure device or surgically. ASD closure is indicated when right heart enlargement is present, however not in the presence of severe pulmonary hypertension and Eisenmenger’s syndrome.