Options
ATRIAL SEPTAL DEFECTS
- ATRIAL SEPTAL DEFECTS
-
ATRIAL SEPTAL DEFECTS
exam > 11-08-2014, 12:10 PM
ASDs are some of the most common congenital defects,
representing 10% to 17% of cases, with a higher prevalence
in women (60%). Defects are classified according to their
location in the interatrial septum. The most common ASD
(60%), the ostium secundum defect, involves the fossa
ovalis. Ostium primum defects (20%) involve the atrioven-
tricular junction and are at one end of the spectrum of atrio-
ventricular septal defects (or endocardial cushion defects).
Primum ASDs are usually associated with a cleft mitral valve
and mitral regurgitation. In rare cases, primum ASD can be
associated with a large VSD and a single atrioventricular
(AV) valve, forming an AV septal defect. Sinus venosus
defects are located in the superior septum and may be associ-
ated with partially anomalous pulmonary venous drainage
into the superior vena cava or right atrium.
In patients with uncomplicated ASDs (e.g., with normal
pulmonary vascular resistance), oxygenated blood shunts
from the left to the right atrium. The magnitude of the
shunting is determined by the size of the defect and the
compliance of the left and right ventricles. Small ASDs
accommodate the increased blood flow in the right atrium
without sequelae and no significant hemodynamic compro-
mise of the right heart. If the defect is large, the right atrium
and right ventricle dilate to accommodate the increased
volume of shunted blood (Fig. 7-1). Pressure in the pulmo-
nary artery increases secondary to the increased volume
of blood; however, with the exception of extremely large,
long-standing defects, pulmonary vascular resistance usually
remains normal.
Most patients with ASD are asymptomatic until adult-
hood, when symptoms such as fatigue, dyspnea, and poor
exercise tolerance develop, secondary to right ventricular
dysfunction. Older patients may decompensate when
acquired heart disease leads to a rise in left ventricular filling
pressures and more blood is shunted from the left atrium to
the already volume-overloaded right heart. Patients with
ASD are prone to atrial fibrillation, especially after 50 years
of age. Irreversible pulmonary vascular obstruction resulting
in right-to-left shunting and cyanosis (Eisenmenger syn-
drome) is uncommon and occurs infrequently (<5% of
patients with ASDs). The presence of an ASD may be her-
alded by a paradoxical embolus traversing the defect, result-
ing in stroke or transient ischemic attack.
A prominent right ventricular pulsation may be observed
on physical examination, along the left sternal border sec-
ondary to a dilated, hyperdynamic right ventricle (Table
7-1). The S2 sound is widely split and fixed. Wide splitting
occurs because right ventricular volume overload results in
a prolonged ejection period and delayed closure of the pul-
monic valve. Fixed splitting results from a lack of respiratory
variation in right ventricular filling with variation in the left-
to-right shunt, compensating for varying venous return. An
ejection-quality murmur that increases with inspiration is
commonly heard at the left sternal border and is secondary
to increased blood flow across the pulmonic valve. If severe
pulmonary vascular obstruction develops, the P2 sound
becomes loud, the splitting of S2 narrows, and a right ven-
tricular gallop may be heard.
The diagnosis of ASD is usually made with two-dimen-
sional and color Doppler echocardiography. In particular,
transesophageal imaging allows for excellent visualization of
the interatrial septum as well as associated congenital defects
such as anomalous pulmonary veins, VSDs, and abnormali-
ties of the mitral leaflets. This technique provides additional
information pertaining to right ventricular size and function
and the degree of shunt flow. Cardiac magnetic resonance
imaging (MRI) is another noninvasive imaging modality
that provides excellent visualization of the interatrial septum
and pulmonary veins and can provide diagnostic informa-
tion in cases of uncertainty after echo imaging. MRI is par-
ticularly well suited for analysis of right ventricular size
and function. Cardiac catheterization is useful to assess and
define the shunt fraction (Qp/Qs ratio) to measure pulmo-
nary arterial pressures and to estimate pulmonary vascular
resistance, but is rarely necessary after noninvasive imaging.
The most common indication for catheterization is now the
identification of concomitant coronary artery disease in
adults older than 40 years who are contemplating surgical
repair.
Once diagnosed, ASDs should be closed without delay.
The presence of right ventricular enlargement should prompt
referral for closure, even in the absence of symptoms. Para-
doxical embolism, elevation of pulmonary artery pressure,
or a net left-to-right shunt should also prompt consideration
of closure. Defects less than 8 mm in diameter are rarely
significant. Significant pulmonary hypertension is a con-
traindication to ASD closure. When pulmonary arterial
pressures exceed two thirds of systemic pressure, evidence of
ongoing significant left-to-right shunt must also be present,
or the reversibility of pulmonary hypertension with the
administration of vasodilators or oxygen must be adminis-
tered to justify the increased risk for closure.
Percutaneous device closure of a secundum ASD is an
acceptable alternative to surgical closure and is becoming the
preferred intervention for this condition. A sufficient rim of
tissue is required for successful device deployment. Short-
and intermediate-term results with the Amplatzer closure
device have been excellent. The long-term results remain
unknown, and patients who have received such devices
should continue to receive close follow-up care. Primum
and sinus venosus defects should be surgically closed.
Closure of a hemodynamically significant ASD before the
age of 25 years is expected to convey a mortality benefit.
Closure before the age of 40 years of age is expected to
decrease the long-term risk for atrial arrhythmias. After the
fourth decade, symptoms are usually significantly improved
after surgical repair; however, some degree of right ventricu-
lar dysfunction may persist. Antibiotic prophylaxis for infec-
tive endocarditis is not required for small ASDs or patent
foramen ovale or after ASD closure.
