A A PILLAI, A HANDA, V BALASUBRAMANIAN, SARANYA GOUSY Atrial septal defects (ASDs) are common, constituting approximately 8–10% of congenital heart disorders, with a reported prevalence at birth of approximately 2 per 1000 live births. The clinical consequences of an ASD are related to the anatomic location of the defect, its size and the presence or absence of other cardiac anomalies.1 ASDs may be related to mutations in regulatory genes or sarcomeric genes. Heterozygous mutations in NKX2.5 were first reported in families with ostium secundum ASD as autosomal dominant inheritance. Mutations in other transcription factors such as TBX5, GATA4, TBX 2.0 have also been reported. Although most ASDs occur sporadically, familial mode of inheritance has been reported. ASDs have been reported to occur along with cardiomyopathies and are also associated to occur with syndromes such as Noonan, Down, Williams and Ellis-van Crevald. In addition to above-mentioned genetic diseases, they are also associated with maternal and environmental risk factors such as diabetes, anticonvulsants, anti-inflammatory drugs, retinoids, smoking and alcohol. The risk of congenital heart disease in the offspring of women with ostium secundum ASD is higher. The various types of ASDs are classified on their different anatomic locations and abnormal embryogenesis: Secundum ASD Primum ASD Sinus venosus ASD Coronary sinus ASD Patent foramen ovale (PFO) is also an open communication between the right and left atria; however, PFO is not considered an ASD because no septal tissue is missing. Secundum defects—Secundum defects constitute approximately 75% of all ASDs and occur twice as often in females as in males.2–5 Familial recurrent rate has been estimated to be about 7–10%.6,7 A comprehensive review reported an incidence of 564 per million live births. The true incidence of secundum ASD may be much higher as many ASDs are commonly undiagnosed in infancy and childhood and spontaneously resolve before detection. Secundum ASDs are located typically within the fossa ovalis (remnant of the foramen ovale in the right atrium). This type of ASD can result from arrested growth of the secundum septum or excessive absorption of the primum septum (Figure 1.1). If the floor of the fossa ovalis is fenestrated, multiple defects can be seen. The defects can vary greatly in size, from less than 5 mm to greater than 20 mm. Figure 1.1 (a) The normal atrial septum as well as various types of ASDs is shown. (b) Secundum ASD formed by the poor growth of the septum secundum or excessive absorption of the septum primum. (c) Primum ASD formed by the failure of the septum primum to fuse with the endocardial cushions. The fossa ovalis is normal. The frontal view of the primum ASD shows the caudal location of the ASD just above the endocardial cushions. (d) Sinus venosus ASD caused by the malposition of the insertion of the superior or inferior vena cava and is outside the area of the fossa ovalis. (Illustration by Saranya Gousy.) Secundum ASDs may be associated with or continuous with other ASDs, such as a sinus venosus defect or a primum defect. Some patients with secundum ASD have functional mitral valve prolapse, perhaps related to a change in the left ventricular geometry associated with right ventricular volume overload.8,9 Primum defects—The primum type ASD develops if the septum primum does not fuse with the endocardial cushions, leaving a defect at the base of the interatrial septum that is usually large (Figure 1.1
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Classification and natural history
INTRODUCTION
CLASSIFICATION
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