Atrial septal defect (ASD) is one of the most common congenital heart defects with an estimated incidence of 6 to 10 per 10,000 live births. Atrial septal defects are classified as primum, secundum, sinus venosus, and coronary sinus defects. The onset of symptoms vary among different patients, and many patients remain asymptomatic. Larger defects tend to cause symptoms early on, and smaller defects cause symptoms later in life. Symptoms include failure to thrive, shortness of breath, palpitations, enlargement of right heart chambers, peripheral edema, cyanosis, orthodeoxia-platypnea, and paradoxical embolism. Transcatheter closure of the ASD is currently available for secundum type of ASDs, and currently, there are two FDA-approved devices in the United States for the closure of ASD.
The heart comprises four chambers; the two upper chambers are referred to as the atria, and the two lower chambers are referred to as the ventricles. The inter-atrial septum divides the atrium into the right, and the left atria. Similarly, there is a septum that separates the ventricles into the right and left and is called as the inter-ventricular septum. Embryologically the inter-atrial septum is derived from the septum primum and the septum secundum. The septum primum arises from the roof of the atrium and develops towards the endocardial cushions covering the ostium primum. This is followed by degeneration of the septum primum towards the roof of the atria creating the ostium secundum. Next, the septum secundum arises from the atrial roof on the right atrial side and grows caudally to cover the ostium secundum. Depending on the location of the defect, ASDs are classified into primum, secundum, sinus venosus, and coronary sinus defects. Defects of the inter-atrial septum at the site of the ostium secundum (fossa ovalis) are referred to as secundum type ASD, and this is the most common type of ASD. The primum defects involve the ostium primum and the endocardial cushions and are associated with atrioventricular valvular abnormalities. The sinus venosus defects are located at the junction of the superior or inferior vena cava with the right atrium and are called as superior and inferior sinus venosus defects in relation to the superior or inferior vena cava. The superior sinus venosus defects are associated with anomalous pulmonary vein connections. In the coronary sinus defect, there is a loss of the roof of the coronary sinus that allows for direct communication between the left atrium and the coronary sinus. Based on size, ASDs are classified into:
Transcatheter closure of the ASD can be performed for only the secundum type of ASDs. The other ASD types are repaired surgically because of their location and associated abnormalities of atrioventricular valve defects (primum type) and anomalous pulmonary vein connections (sinus venosus type).
Current indications for ASD closure by a transcatheter approach include:
Contraindications for ASD closure by a transcatheter approach include:
Interventional cardiologist trained and/or experienced in structural heart disease, cardiovascular cath laboratory nurse, first assistant, and cardiac cath laboratory technician.
The patient should be evaluated clinically and through history including any allergies should be assessed especially to metals such as nickel. The patient should undergo a transesophageal echocardiogram to evaluate the type of ASD and its suitability for repair, for example, assessment of the rims of tissue around the ASD. The defect size should be measured to size the device. The patient should also undergo a right heart catheterization to assess the pulmonary pressures and the shunt fraction. Cardiac magnetic resonance imaging or cardiac CT angiography is recommended to assess the defect and for anomalous pulmonary vein connections if this cannot be assessed during the transesophageal echocardiogram.
Once eligibility is determined the patient should be counseled about the risks and benefits of undergoing the procedure and consent should be obtained. On the day of the procedure, the patient should be evaluated for any active ongoing infections and determine suitability for anesthesia.
Transcatheter closure of ASD is performed under moderate sedation or general anesthesia. After sedating the patient vascular access is obtained in the femoral vein. Usually, two venous access points are obtained: one for the delivery sheath and the other one for ICE catheter. Additional arterial access may be obtained for pressure monitoring depending on the operator. The patient is anticoagulated to maintain an ACT of 250 to 300. If an intracardiac echo is not used then transesophageal echocardiogram is needed to guide the procedure. The ICE or TEE is used to visualize the interatrial septum, and the ASD is identified, and color Doppler interrogation is performed, and the defect size is measured. Next, a multipurpose catheter along with guidewire is advanced into the right atrium, and the defect is crossed, and the wire is advanced into the left superior pulmonary vein, and the catheter is advanced into the left superior pulmonary vein. Next, the guidewire is exchanged for a stiff guidewire, and the catheter is removed. Next, an ASD sizing balloon is advanced into the defect over the wire and the balloon is inflated with a mixture of diluted contrast and the defect size is estimated under fluoroscopy and ICE/TEE using a stop-flow technique.
Once sizing of the device is performed, appropriate size device is selected and is prepped and loaded on to the delivery catheter. After this the sizing balloon is removed and the delivery catheter is advanced over the wire in to the left atrium and the guidewire is removed. After this, the septal occluder device is advanced into the delivery catheter into the left atrium, and the left atrial disc is unsheathed, and after this, the delivery catheter is retracted into the right atrium, and the right atrial disc is unsheathed under fluoroscopic and ICE/TEE guidance. After this the ASD is interrogated using ICE/TEE for complete sealing of the defect by the device and the stability of device is verified. After this the occluder device is released and again the ASD is interrogated for complete sealing and stability of the device. After this, the ICE catheter and delivery sheath are removed, and hemostasis is achieved using manual pressure or a figure 8 stitch. The patient is maintained on dual antiplatelet agents for about 3 to 6 months after the procedure.
Current guidelines recommend either surgery or transcatheter closure of the secundum ASD. However, transcatheter closure of the ASD is a relatively safe and effective procedure for closure of the ASD in appropriately selected patients and is associated with low morbidity. Therefore, transcatheter closure has become the choice of therapy for the closure of secundum ASD defects.
Transcatheter ASD closure is a relatively safe procedure with a low complication rate and faster recovery. A multidisciplinary heart team approach is recommended for a thorough evaluation of the patient by a cardiologist and an interventional cardiologist experienced in the treatment of structural heart disease to assess the appropriate treatment strategy for every patient. Typically, these procedures should be performed at high-volume centers to obtain optimal outcomes.