Atrial Septal Defect

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Atrial septal defect is an abnormal opening between the atria, allowing blood from the high-pressure left atrium to flow into the lower-pressure right atrium. There are three types of ASD: Ostium primum (ASD 1): Opening at lower end of septum; may be associated with mitral valve abnormalities; Ostium secundum (ASD 2): Opening near center of septum; and Sinus venosus defect: Opening near junction of superior vena cava and right atrium; may be associated with partial anomalous pulmonary venous connection. The pathophysiology explains that because left atrial pressure slightly exceeds right atrial pressure, blood flows from the left to the right atrium, causing an increased flow of oxygenated blood into the right side of the heart. Despite low pressure difference, a high rate of flow can still occur because of low pulmonary vascular resistance and the greater distensibility of the right atrium, which further reduces flow resistance. This volume is well tolerated by the right ventricle because it is delivered under much lower pressure than with a VSD. Although there is right atrial and ventricular enlargement, cardiac failure is unusual in an uncomplicated ASD. Pulmonary vascular changes usually occur only after several decades if the defect is left unrepaired. The clinical manifestations show that patients may be asymptomatic. They may develop heart failure. There is characteristic systolic murmur with a fixed split second heart sound. There may also be a diastolic murmur. Patients are at risk for atrial dysrhythmias (probably caused by atrial enlargement and stretching of conduction fibers) and pulmonary vascular obstructive disease and emboli formation later in life from chronically increased pulmonary blood flow.

References

Hockenberry, M. J. (2018). The child with cardiovascular dysfunction. In S. E. Perry, D. Leonard Lowdermilk, K. Cashion, K. Rhodes Alden, E. F. Olshansky (Assoc. Ed.), M. J. Hockenberry, D. Wilson, & C. C. Rodgers Maternal child nursing care (6th ed.), (pp. 1224-1270). St. Louis, MO: Elsevier, Inc.