EPIDEMIOLOGY AND PATHOGENESIS
Atrial septal defects (ASDs) include a group of abnormalities that result in a communication between the right and left atria. They are among the most common of all congenital heart defects with a prevalence of 1.6 per 1000 births worldwide.1
In the absence of additional pathology, ASDs result in a left-to-right shunt. Although almost uniformly these shunts occur at low pressure owing to relatively passive blood flow between two low-pressure chambers, the long-standing volume load on the right atrium, right ventricle, and pulmonary artery vasculature may lead to atrial arrhythmias, right-sided chamber enlargement and dysfunction, and, rarely pulmonary arteriolar hypertension.2
There are several types of ASDs, each resulting from a unique developmental abnormality (Figure 106.1)
. Most commonly encountered are secundum ASDs, which are located within the fossa ovalis, resulting from defects within the septum primum. Secundum defects vary greatly in size and shunt volume. Primum ASDs result from incomplete septation at the crux of the heart where the atrioventricular (AV) valves and atrial and ventricular septa meet and are part of a larger constellation of abnormalities known as endocardial cushion defects or AV septal abnormalities. These lesions, by definition, involve abnormalities of the developing AV valves and are often associated with ventricular septal defects (VSDs). As such, treatment indications and considerations for primum ASDs are described in a separate section (see section “Atrioventricular Septal Defects”). Sinus venosus ASDs are located superiorly at the junction of the superior vena cava (SVC
) and the roof of the right atrium. These defects result from a deficiency in the development of the wall that normally separates the right pulmonary veins from the SVC
and are accompanied by a posterosuperior ASD
Thus, the definition of a sinus venosus ASD
includes abnormal pulmonary venous return and typically results in a significant left-to-right shunt. The least common of all ASDs, an unroofed coronary sinus, results from a deficiency of the septal tissue surrounding the ostium of the coronary sinus, creating a communication between the atria.
Atrial septal defect anatomy. ASD
, atrial septal defect.
CLINICAL PRESENTATION AND DIAGNOSIS: ATRIAL SEPTAL DEFECTS
A substantial proportion of adult patients with an undiagnosed ASD
have minimal to no recognizable symptoms. When present, the most common symptom is mild to modest exertional dyspnea. Frequently, it is only after an ASD
is repaired that long-standing exertional intolerance is realized in retrospect. In the presence of large shunts or advanced age, symptoms of congestive heart failure may manifest. ASDs are also associated with early-onset atrial arrhythmias, and younger patients presenting with new-onset atrial fibrillation should prompt further evaluation for structural cardiac abnormalities.
Physical examination findings are often unremarkable; however, cardiac auscultation may reveal subtle signs of excessive pulmonary blood flow. A fixed split S2 may be heard throughout the respiratory cycle, and a pulmonary systolic flow murmur may be present over the second intercostal space. In rare cases, a loud and palpable P2, jugular venous distension, or dependent edema may be present as a sign of either significant pulmonary hypertension or right ventricular dysfunction.
An electrocardiogram (ECG
) may reveal evidence of right atrial enlargement and a right bundle branch block with or without right axis deviation. Septum primum defects are the exception with a right bundle branch block associated with left axis deviation. Sinus venosus defects may show an ectopic atrial rhythm (ie, negative P waves in the inferior ECG
leads). Transthoracic echocardiography (TTE
) typically establishes the diagnosis demonstrating evidence of flow between the atria on color Doppler; however, transesophageal echocardiography (TEE
) provides a more comprehensive assessment of defect anatomy. Sinus venosus defects and associated abnormal pulmonary venous return are frequently difficult to visualize in an adult by TTE
imaging. A significantly dilated right ventricle without identifiable intracardiac pathology by TTE
should raise concerns for this diagnosis and prompt further evaluation with either a TEE
or cross-sectional imaging. Cross-sectional imaging with either cardiac magnetic resonance (CMR
) imaging or a cardiac computed tomographic angiogram (CCTA
) provides an excellent assessment of sinus venosus anatomy and the number and location of anomalous pulmonary venous drainage. Both CMR
are useful adjuncts in other types of ASDs and offer accurate assessment of chamber size, presence of additional abnormalities, and, in the case of CMR
, an estimate of the shunt magnitude.
Shunt lesions management. ASD
, atrial septal defect; PAPVC
, partial anomalous pulmonary venous connection; PDA
, patent ductus arteriosus; PVR
, pulmonary vascular resistance; SVR
, systemic vascular resistance; VSD
, ventricular septal defect.
Cardiac catheterization can aid in the diagnosis by confirming the presence of a shunt. Often, direct passage of a catheter through the defect is possible, helping to identify shunt location. Additionally, cardiac catheterization provides important hemodynamic information regarding intracardiac filling pressures, shunt magnitude, and pulmonary vascular resistance, all of which may influence treatment decisions.
MANAGEMENT: ATRIAL SEPTAL DEFECTS
ASD closure is recommended in the presence of impaired functional capacity, right atrial or ventricular enlargement, right ventricular dysfunction, or paradoxical embolism (Algorithm 106.1)
. Closure is not recommended and possibly harmful in the presence
of significant pulmonary vascular resistance at greater than one-half to two-thirds systemic levels.4
These patients should be comanaged with a pulmonary hypertension specialist.
Both surgical and transcatheter techniques exist for ASD
closure; however, not all ASDs allow for transcatheter closure at present. Transcatheter ASD
closure is the treatment of choice for secundum ASDs when anatomically feasible. In the presence of adequate circumferential tissue, device closure of secundum ASDs has a high rate of success at low risk.5
Device embolization is infrequent and often successfully managed in the cardiac catheterization laboratory.6
Device erosion is a life-threatening complication often requiring urgent surgical intervention. This rare complication remains poorly understood and, while associated with ASD
rim tissue deficiency, no single identifiable subpopulation is recognized to be at substantially elevated risk to warrant contraindication of device closure.7
Surgery remains the mainstay of therapy for individuals with primum ASDs, sinus venosus defects, and unroofed coronary sinuses; however, new transcatheter techniques are emerging for the treatment of a subpopulation of sinus venosus lesions.8
closure remains an effective option for those with contraindications to transcatheter closure with very low mortality and an excellent long-term prognosis.5
In general, patients with an indication for ASD
closure who are not eligible for transcatheter occlusion should be referred for surgery.
FOLLOW-UP PATIENT CARE: ATRIAL SEPTAL DEFECTS
Lifelong follow-up is typically recommended regardless of whether the ASD
has been treated. Post ASD
device closure, patients should receive intermittent imaging follow-up within the first year to evaluate for device malposition, residual shunting, and erosion. Long-term follow-up is recommended following device and surgical closure every 3 to 5 years with an ECG
imaging to assess for new-onset atrial arrhythmias, residual shunting, right ventricular size and function, pulmonary artery pressures, and, in the case of device closure, late erosion.4
Patients in whom ASD
closure has not been pursued, long-term follow-up every 3 to 5 years with either TTE
or cross-sectional imaging is recommended in the absence of chamber enlargement, ventricular dysfunction, or elevated pulmonary artery pressures.