• Heart is positioned such that the the inferior border is
facing towards your left. View of inflow tract of rt. V..
• Note the thin transluscent tricuspid valve between the
right ventricle below and atrium above.
• Note the 2 defects (arrow) just above the T.valve ring.
• Note the curved rim of the fossa ovalis just above the
handle of the arrow. This is the inferior margin of the
septum secundum, with the septum below it being of
septum primum origin.
• This is therefore a defect of the septum primum type.
|Arial Septal Defect (ASD)|
•Unknown in > 90% of cases. Identifiable chromosomal
abnormalities in 5% of cases, i.e. trisomies 18 & 21.
•Clear that etiology not entirely genetic, since
only one of monozygotic twins may develop an anomaly,
and rubella in the mother during the first
trimester leads to congenital heart disease (CHD) and a variety of defects in
other systems, including immunodeficiencies.
•Definite evidence of radiation, and chemicals also
being etiologic factors.
•Septum primum, septum secundum, and the sinus
venosus are involved anlagen in three types of defects.
•Failure of S. primum to form completely results in a
low ASD adjoining AV valve.
•Failure of normally partially formed S. secundum to
reach antero-inferiorly far enough, &/or excessive S.
primum resorption results in fossa ovalis ASD^s.
•Primitive sinus venosus contributes to atrial walls,
septum, ostia of superior and inferior vena cavas and pulmonary veins.
•Defects form high or low in septum near V. cava ostia.
•ASD found in 5% of all cases of CHD.
•CHD most common form of heart disease in childhood.
•Incidence is 6-8/1000 live full term births.
•Incidence higher in stillborns and premature births.
•90% of ASD^s are of the septum secundum type, and 5%
of the septum primum type.
•A left to right atrial shunt increases pulmonary blood
flow, but may be asymptomatic throughout life if the
defect is much less than 1 cm in diameter.
•Arrhythmias and a murmur developing in the third
decade with larger defects prompt evaluations for
corrective low risk surgery to prevent later
potential pulmonary hypertension.
•Chronic 2-4 X normal pulmonary blood flow may provoke
pulmonary hypertension with right to left shunt and
heart failure in less than 10% of cases.
|General Gross Description|
•Septum primum defects are adjacent to AV valve ring,
antero-inferior to fossa ovalis.
•Septum secundum defects form within the fossa ovalis
or along its superior margin if S. secundum development
•Sinus venosus defects are located immediately adjacent
to the ostia of the superior or inferior vena cavas,
and are often associated with anomalies of pulmonary
venous drainage into the right atrium or superior vena
|General Micro Description|
•Individual layers of involved structures are histologically normal.
• Cotran RS et. al.: Robbins Pathologic Basis of Disease. 5th edition. Philadelphia, W.B. Saunders, 1994, pp. 573-4.
• Harrison^s Principles of Internal Medicine, 13th Edition: Isselbach et. al. (eds). New York, McGraw-Hill, 1994, pp. 1040-1.