Atrial Septal Defects

Introduction

• ASDs are abnormal communications between the left and right atria of the heart. They are the second most common CHD lesion in children, accounting for 5-10% of CHD. A patent foramen ovale is present in up to 25% of adult hearts.¹
• ASDs can occur as an isolated defect (Figure 1) or as part of a more complex CHD. In some forms of CHD (e.g., transposition of the great arteries (Link), total anomalous pulmonary venous return (Link) or single ventricle lesions (Link) an atrial communication is necessary to allow blood from the pulmonary and systemic circulations to mix.

• ASDs are classified based on their location (Figure 2).
  • Secundum ASD (80%) – within the area bordered by the limbus of the fossa ovalis
  • Primum ASD – within the septum primum in close proximity to the tricuspid valve
  • Sinus Venosus ASD – near the superior vena cava (more common) or inferior vena cava (less common) orifice, sometimes associated with partial anomalous venous return of the proximal pulmonary vein
  • Coronary Sinus ASD (“unroofed coronary sinus”) – in the left atrium, where the wall between the roof of the coronary sinus and the inferior left atrium is absent

Etiology

Embryology

• ASDs occur when there is incomplete formation of the interatrial septum during the 4th – 5th weeks of fetal development:
  • Secundum ASD – results from incomplete development of the septum secundum or excessive resorption of the septum primum
  • Primum ASD – results from incomplete fusion of the septum primum and the endocardial cushions
  • Sinus venosus ASD – results from abnormal incorporation of the sinus venosus into the right atrium
  • Coronary sinus ASD – results from incomplete development of left atrial venous folds

Genetic Factors

• Aneuploidies: ASDs are associated with Trisomy 21, Trisomy 18, Trisomy 13, and Turner (XO) syndrome.
• Single-gene disorders: ASDs are associated with a number of genetic anomalies, including Holt-Oram, Noonan, Treacher Collins, TAR (thrombocytopenia absent radius), and Ellis-van Creveld syndromes.

Environmental Factors

• First-trimester rubella, as well as maternal diabetes and systemic lupus erythematosus, have been associated with ASDs.
• Maternal exposure to tobacco, alcohol, and cocaine have been linked to VSDs as have prescribed medications such as paroxetine, although the data for maternal antidepressant use is conflicting.²

Pathophysiology

• The amount and direction of blood shunted through an ASD are dependent upon the size of the defect and relative compliances of the right and left ventricles.
• Pressure in the right atrium is normally lower than that of the left, leading to a primarily left-to-right shunt. Bidirectional and right-to-left shunting are possible and contribute to the risk of paradoxical emboli and cerebrovascular accidents.
• Right-sided volume overload from left-to-right shunting leads to right-sided volume overload that may, if left untreated, progress to right-sided heart failure.
• Right atrial enlargement causes electrical remodeling and increases the risk of arrhythmias.³
• Although uncommon, the increase in pulmonary blood flow may lead to remodeling of the pulmonary vasculature and an increase in pulmonary vascular resistance, leading to pulmonary hypertension. As right-sided pressures increase, shunt reversal may occur, causing cyanosis (Eisenmenger’s syndrome) from right-to-left shunting.

Diagnosis

Presentation

• Patients presenting with small or moderate-sized ASDs are usually asymptomatic. A soft, midsystolic (ejection) murmur, low-pitched diastolic murmur, and/or a widely split S2 may be heard on auscultation. A parasternal heave may also be present.
• Larger ASDs may present with slow weight gain, frequent upper respiratory tract infections, and exercise intolerance that progress to fatigue, dyspnea on exertion, and palpitations or arrhythmias in older patients.
• Eisenmenger’s syndrome is a rare presentation of ASD.
• Systemic thrombotic events (i.e., transient ischemic attack, cerebrovascular accident, unprovoked arterial thrombosis/embolism) should raise the suspicion for ASD.

Diagnostic Studies

• Electrocardiography (ECG) is most likely normal in patients with small ASDs. The crochetage sign, a notch near the R-wave peak in the inferior leads is highly sensitive and specific for ASD (Figure 3).⁴ Larger defects may show right (secundum) or left axis deviation (primum and sinus venosus), right ventricular hypertrophy/strain, and/or first-degree atrioventricular (AV) block (especially primum type defects) or incomplete right bundle branch block.
• Chest radiography may show increased pulmonary vascular markings and an enlarged cardiac silhouette in patients with larger ASDs.
• Transthoracic echocardiography (TTE) is the most commonly used modality to diagnose ASD. TTE delineates the location and size of defects, identifies other cardiac anomalies, assesses the degree of right-sided volume overload, and provides hemodynamic information such as estimated right-sided ventricular pressure and an estimation of pulmonary to systemic flow ratio.
• ASDs (especially secundum type) can be missed on fetal Echo due to obligate flow through the foramen ovale in utero.
• Cardiac computed tomography (CT) or magnetic resonance imaging (MRI) may be appropriate in identifying the presence and location of partial anomalous pulmonary venous return in patients with sinus venosus defects.
• Cardiac catheterization is rarely indicated for diagnostic purposes unless there is a concern for pulmonary hypertension.

Treatment Strategies

General

• Most ASDs (more than 80%) are less than 8mm in diameter and diagnosed before 3 months of age, close spontaneously by 15 months of age, whereas those >/= 8mm rarely close spontaneously.⁵
• Secundum ASDs diagnosed outside of the neonatal period or early infancy are also unlikely (less than 5%) to spontaneously close, with up to two-thirds increasing in size over time.⁶
• Closure is recommended for pediatric patients with substantial left-to-right shunting (right atrial and/or ventricular enlargement on echocardiography, signs or symptoms of pulmonary overcirculation, and/or Qp:Qs ratio greater than 2:1) or with a history of paradoxical embolism.
• ASD closure is generally deferred until after 2 years of age.

Percutaneous Device Closure

• Percutaneous device closure is the preferred intervention for secundum ASDs, provided that the anatomy is favorable (i.e., not excessively large and with a sufficient rim of tissue around the defect to allow for device seating without obstruction to the coronary sinus, vena cavae, pulmonary veins, or AV valves).
• Device closure is associated with a shorter length of stay and a lower complication rate.
• Complications include procedural failure, residual shunt, device embolization or malposition, cardiac perforation, pericardial effusion, arrhythmia, and injury to the femoral vessels.⁷

Surgical Closure

• Surgical closure is indicated in infants with heart failure, patient/parental preference, and in patients with unfavorable anatomy (secundum ASD with insufficient rims, other types of ASD not amenable to device closure).
• Complications include bleeding, patch dehiscence, arrhythmia, pneumothorax, pleural effusion, and wound infection.⁷

Anesthetic Considerations for Interventional/Surgical Management

Preoperative Evaluation

Labs

• Complete blood cell count +/- coagulation studies
• Basal metabolic profile to assess renal function and electrolyte disturbances if on diuretics
• Type and crossmatch

Imaging/Diagnostics

• ECG, echocardiography +/- MRI, CT
• Cardiac catheterization in patients with concern for pulmonary hypertension
• Chest radiograph

Intraoperative Management

Monitoring

• Standard American Society of Anesthesiologists monitors
• Transesophageal echocardiogram
• For surgical closure: Near-infrared spectroscopy, invasive pressure monitoring (arterial pressure +/- central venous pressure)

Access

• Two large-bore peripheral intravenous (IV) catheters
• For surgical procedures: arterial line, +/- central venous line

Anesthesia Technique

• General endotracheal anesthesia is typically used.
• Air bubbles must be avoided in the IV lines.
• For surgical repair, regional or neuraxial techniques may be performed for postoperative analgesia.

Hemodynamic Goals

• Hemodynamic goals include maintaining adequate preload, normal sinus rhythm, and myocardial contractility.
• Inhalational induction is usually well-tolerated in patients with good ventricular function, normal RV pressures, mild symptoms, and no signs of pulmonary hypertension. Patients may be hypovolemic due to diuretic therapy and may require additional fluids.
• In surgical cases, there is generally not a great need for inotropic support post-cardiopulmonary bypass. Patients may require vasodilators such as nicardipine or nitroprusside for blood pressure control. Bleeding is not extensive, and blood products are usually not needed.

Postoperative Care

• Following transcatheter closure, antiplatelet therapy should be initiated and patients should be monitored for device migration.
• Following device closure, patients should be monitored for postoperative bleeding, arrhythmia, residual shunting, and effusions.
• Subacute bacterial endocarditis prophylaxis is recommended for six months after surgical or percutaneous closure. Beyond 6 months, it is indicated is there is residual shunting next to the device or prosthetic material.