Atrial Septal Defect
Anatomic Types
Patent Foramen Ovale (PFO)
PFO has been documented in 50% of children 1-5 years of age and in over 25% of adults over 20 years of age. This type of an ASD results from the lack of fusion between the septum primum and secundum, and may allow for right to left shunting in patients with high right sided pressures. It may also cause an emboli to enter the systemic circulation and result in arterial ischemic events.Ostium Secundum
This is the most common type of ASD, accounting for about 80%. It results from reabsorption of the septum primum producing an opening, or creating a short septum primum that cannot close the foramen ovale.Sinus Venosus
This type is found high in the atrial septal wall above fossa ovalis close to the junction of the superior vena cava and right atrium. This results either from the abnormal development of the septum secundum, or by the failure of sinus venosus to be absorbed into the atrial wall. * Sinus Venosus type is usually accompanied by partial anomalous venous return.Common Atrium
Atrial septum may fail to develop entirely thus resulting in a single atrial chamber. May be associated with endocardial cushion defects.
Pathophysiology
The primary pathologic process in all septal defects is the shunting of blood from one cardiac chamber to another. The relative compliance of the chambers and the area of the defct will determine the degree and direction of the shunt. Compliance would take preference in this determination because it represents the filling resistance of each chamber. Pulmonary vascular resistance decreases as the infant ages and left to right shunting occurs. Pulmonary blood flow thus tends to increase. Once the pulmonary to systemic flow ratio (Qp/Qs) exceeds three symptoms of pulmonary congestion begin to manifest. When PVR increases, right ventricular hypertrophy begins to develop with the eventual decrease in the volume of left to right shunt. Eventually, reversion of the shunt occurs resulting in cyanosis.
Hemodynamically insignificant ASD's have no effect on the life span, however, they may increase the risk of bacterial endocarditis and paradoxical emboli.
Symptoms
Young children will manifest frequent respiratory infection, adults may complain of fatigue and dyspnea. Systolic murmur is present as well as a tricuspid flow murmur resulting from tricuspid stenosis secondary to left to right shunting. EKG may show an incomplete right bundle branch block. There will be an increase in atrial oxygen saturation levels at catheterization.
Right to left shunting manifests in clubbing and cyanosis, diastolic murmur of pulmonic regurgitation may also be present. RV hypertrophy and enlargement of the main PA artery are present on the chest x-ray.
Surgical Intervention
Surgical closure of ASD is recommended preferable at 3-5 years of age. Standard midline sternotomy is recommended, and either suturing or patch is attempted based on the size of the defect.
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