Congenital malformations - Edocr

Chapter 27
Septal Defects
BARBARA K. BURTON
ATRIAL SEPTAL DEFECT
(EXCLUDES PATENT FORAMEN
OVALE)
INTRODUCTION
Atrial septal defect (ASD) is a defect in the atrial
septum which leads to a communication between
the right and left atrium. The most common form
is the secundum type of ASD which represents
85% of all ASDs and 8–10% of all congenital
heart defects.
DIAGNOSIS
Most infants with a secundum ASD do not have
symptoms and the defect is rarely diagnosed in
the neonatal period unless an echocardiogram
is performed. The diagnosis is usually made
when a child is evaluated for a systolic murmur
which may be difficult to distinguish from the
murmur of pulmonic stenosis. The characteristic
finding of an ASD is a fixed split second heart
sound, however. When a large left to right shunt
is present, a mid-diastolic murmur can be heard
across the tricuspid valve in addition to the systolic
murmur across the pulmonic valve. Chest
radiography reveals volume overload on the
right side of the heart and increased pulmonary
vasculature. Electrocardiogram (ECG) reveals
right axis deviation and right ventricular hypertrophy
with an incomplete right bundle branch
block pattern. The defect can be identified by
echocardiography.
INCIDENCE AND ETIOLOGY
ASD usually occurs as an isolated anomaly with
an incidence of close to 1 per 1000 in the general
population. The defect is more common in females
than in males with a sex ratio of 1:2. Although
most commonly isolated, it can be associated with
a number of different malformation syndromes including
chromosome anomalies, single gene disorders,
and teratogenic syndromes. These are
listed in Table 27-1. One of the best known syndromes
associated with ASD is the Holt-Oram syndrome
which is associated with ASD in over 50%
of cases. Other characteristic features of this autosomal
dominant disorder include defects of the
upper limb and shoulder girdle.
Although isolated sporadic cases of ASD are
felt to most often be multifactorial in nature with
multiple genes or genes and environmental factors
playing a role in causation, specific environmental
factors have not been identified. In
some families, ASD may be inherited in a single
gene pattern with autosomal dominant transmission
being well-documented. Two specific
genes have been linked to families in which
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