CHIN: Atrial Septal Defects: Surgical and Transcatheter Management

Atrial septal defects represent a communication between the left and right atria (a hole between the upper chambers of the heart). Simple atrial septal defects were among the first congenital cardiac anomalies to be corrected by surgical treatment. The treatment of these defects was made much easier with the advent of cardiopulmonary bypass. In this article, we will attempt to provide a brief overview, and address the surgical and transcatheter management of common atrial septal defects. We will consider three major types of atrial septal defects: secundum, primum, and sinus venosus.

Secundum atrial septal defect is by far the most common, representing 80% of all ASD’s. It is caused by the failure of a part of the atrial septum to close completely during the development of the heart. This results in an opening in the wall between the atria (a "hole" between the chambers).

Primum atrial septal defects are part of the spectrum of the AV canals, and are frequently associated with a split in the leaflet of the valve, or so called cleft mitral valve.

The sinus venosus atrial septal defect occurs at the junction of the superior vena cava and the right atrium. This represents the floor of the right atrium where blood returns from the upper extremities and head to enter the right atrium. These may frequently be associated with anomalous drainage of the pulmonary veins. This means that one or more of the pulmonary veins, which normally carry oxygenated blood from the lungs back to the left atrium, enters the right atrium instead. There are numerous types of abnormal pulmonary venous connections.

When an atrial septal defect is present, blood can flow ("shunt") across the hole in the from the left atrium to the right atrium. This results in enlargement of the right atrium and right ventricle due to the "extra" blood flowing across the hole, and results in increased pulmonary blood flow.

The majority of patients have few symptoms, however fatigue and shortness of breath are the most common complaints. Because most have no symptoms, atrial septal defects most often are discovered on pre-school entrance examinations when the physician hears a murmur and investigates it. The diagnosis is confirmed by echocardiography, which may visualize the actual defect and estimate its size, as well as the connection of the pulmonary veins. Cardiac catheterization is indicated in cases of an inconclusive echocardiographic examination or associated anomalies which require further evaluation.

Twenty percent of atrial septal defects will close spontaneously in the first year of life. One percent become symptomatic in the first year, with an associated 0.1% mortality. There is a 25% lifetime risk of mortality in unrepaired atrial septal defects. The risk factors associated with increased mortality include the development of a condition in which the pulmonary arteries become thickened and obstructed due to increased flow, from left to right for many years (pulmonary vascular obstructive disease). This is why we electively close ASD’s which have not closed spontaneously by school-age.

Certain types of ASD's (sinus venosus and primum varieties) have no chance of spontaneous closure, and patients with these types of ASD's are not candidates for transcatheter closure because of the location of the ASD (see below). Open heart surgery is indicated for patients with these types of ASD's.

Surgical Treatment
Indications for surgical repair of an atrial septal defect are right ventricular overload (due to flow from the left atrium into the right atrium), a shunt fraction greater than 2.0 as estimated by echocardiography (the amount of blood going to the pulmonary circulation divided by the amount of blood going out to the systemic circulation), and elective closure prior to a child starting school.

The surgical treatment options for an ASD closure include direct suture repair, which is reserved for small atrial septal defects, and the more common patch repair. The material utilized for patch closure of ASD’s may be the patient’s own pericardium, commercially available bovine pericardium, or synthetic material (Gore-Tex, Dacron).

The surgical approach to the atrial septal defect is somewhat dependent upon its location. In general, three surgical approaches may be undertaken:

All types of ASD’s may be approached adequately through a median sternotomy or right thoracotomy. The submammary incision may be the most cosmetic, but makes some ASDs difficult to repair. The primary benefits of the submammary and thoracotomy incisions are cosmetic in nature.

The term "minimally invasive surgery" for repair of atrial septal defects usually refers to repair of the defect using the same techniques as open heart surgical repair (that is, using the heart-lung machine or "cardiopulmonary bypass"), but performing the operation through a much smaller incision. Most children can successfully undergo this type of repair through a small (3-4 inches) incision in the sternum (breastbone). In general, the postoperative course in the hospital is shorter (2-3 days), due to less incisional pain and discomfort.

Once the pericardium is opened, regardless of the choice of incisions, the patient is placed on cardiopulmonary bypass (the heart-lung machine) and blood is diverted away from the right atrium. Cardioplegia (a mixture of medications and nutrients) with high potassium is then administered after the aorta is clamped, thus stopping the heart. The right atrium is then opened to allow access to the atrial septum below. Dependent upon the size and location of the defect, it may be closed directly with sutures or with a patch. Once the defect is closed, the atrial incision is closed as well. The aortic cross clamp is removed, and after normal ventilation is resumed, the patient is warmed and a stable rhythm is achieved , the patient may be weaned from cardiopulmonary bypass. A single drainage tube is placed and the chest is closed.

The results of surgical repair of atrial septal defects are excellent. Surgical mortality is less than one percent, and average hospital stay is four days. These results indicate that ASD’s of all types may be effectively repaired in infants and children with very low mortality and morbidity. Optimal timing for surgery in the asymptomatic child remains prior to starting grade school. The asymptomatic child with an atrial septal defect deserves close follow-up by the pediatrician and pediatric cardiologist, with constant involvement of the cardiovascular surgeon. Should a patient become symptomatic with failure to thrive, or persistent complaints (malaise, respiratory infections, etc.), early surgical intervention would be warranted.

Transcatheter Management
To date, the primary method of therapy for closure of the atrial septal defect (ASD) has been surgical repair. As with all forms of cardiac surgery, there is a small but definite risk of surgical morbidity (5%) and mortality (<1%). Reports of very early results (1950s to 1960s) revealed fairly high death rates and complication rates. In the 1990s, however, marked improvement in surgical technique has contributed to the significantly improved outcomes reported above.

In light of this history, interventional cardiologists explored the possibility of transcatheter closure of the atrial septal defect. This technique involves implantation of one of several devices (basically single or double wire frames covered by fabric) using heart catheterization methods in the cardiac catheterization laboratory, without the need for cardiopulmonary bypass (heart-lung machine), and without the need to stop the heart.

The appropriate selection of patients for this technology is rather strict, and is mainly limited by Food and Drug Administration guidelines. Obvious evidence of enlargement of the right heart (cardiac chambers responsible for pumping blood to the lungs) by chest x-ray, cardiac ultrasound, or previous angiography (dye injection into the heart), or recurrent and frequent lung infections would be principal indicators for closure of these defects. Defects amenable to such device therapy tend to be smaller (less than 20 to 25 mm [3/4 to 1 inch] diameter). Importantly, these lesions must be centrally located within the atrial septum. Defects at the very upper or lower edges of the atrial septum (called ostium primum or sinus venosus) are not good candidates for this procedure, because these defects usually involve other abnormalities of the heart valves, or venous drainage from the lungs. This determination can be made by the patient's primary cardiologist.

Recent data suggest that patients with these types of defects, and a prior history of stroke, may be at a higher risk of stroke recurrence without closure of the atrial defect. At present there are no lower age limitations which preclude device implantation. In many cases, because of the size of the device and its introduction system device, applicability may be limited to patients who weigh more than 8 to 10 kg (18 to 22 lbs).

The usual procedure is very similar to standard heart catheterization. Briefly, flexible long tubes (or catheters) are inserted into the veins and arteries in the groin. We use the knowledge that in all human beings, these vessels are directly attached to the heart, and this is the standard access technique used in all patients. Routine pressures and oxygen levels in all of the chambers of the heart are then obtained. Angiograms (pictures taken following dye injection) are performed to determine the size of the chambers, the size of the defect, and its location within the heart. Using a balloon catheter of a known diameter, the defect is then sized in comparison to the balloon, so that the device appropriate for that particular patient can be chosen. The device is then advanced into the heart through an introducer sheath (larger, less flexible tube).

With most of the presently used devices, half of the device is connected to one side of the atrial septum, and the second half of the device attached to the other portion, forming a sort of "sandwich" of the defect.

Think of this technology as a sandwich cookie, with the cookies themselves being the two halves of the device, and the creme within the two cookies acting as the atrial septal defect. The device is held in place by the natural pressures generated within the atria (upper collecting chambers).

Within six to eight weeks, the device acts as a "skeleton" or a "framework", which stimulates normal tissue to grow in and over the defect. This is how, for example, these devices can be used in growing children; though the device itself does not grow, the tissue that covers the device does, and will continue to grow as the child grows. The time and degree of tissue coverage is still under investigation. The entire procedure is performed under general anesthesia, and the actual implantation of the device is performed using transesophageal echocardiographic guidance (ultrasound pictures using a probe introduced into the esophagus for improved imaging of the heart structures).

There are multiple devices presently being tested under FDA guidelines. There is insufficient space in this report to go into significant detail on all devices. In general, however, successful closure of these defects using a device occurs in 80 to 95% of patients with no significant leak through the defects.

Amplatzer Septal Occluder

CardioSEAL

The major advantage of this technology is its relative non-invasive approach. Patients are usually hospitalized overnight, and many return to work or school within 1-2 days. We have had patients who have been able to resume vigorous exercise (e.g. horseback riding) within 1 week.

Compiling data for all the presently tested devices, the complication rate following transcatheter ASD occlusion is approximately 5%. These complications include the routine risks of cardiac catheterization such as vascular injury (damage to the veins and arteries of the leg), particularly in cases where larger device introducer systems need to be used. Sometimes, problems with blood clotting or excessive bleeding may be seen, particularly in younger patients.

A complication unique to this technology may be the possibility of clot formation on the device itself, with the risk of breakage of the clot causing stroke, or a clot into the vessels of the lung (pulmonary embolus). At present, these problems are addressed by using adequate doses of aspirin or warfarin following the procedure, and by using heparin during the procedure to reduce the clotting factors within the blood. The aspirin or warfarin is used for three to six months, until we are sure that the device is fully scarred in place, and incorporated into the atrial tissue.

The length of and need for antibiotic prophylaxis against infections in the heart (bacterial endocarditis) vary amongst investigators and devices lasting from 12 months following device implant to life-long administration. Most patients are followed at 3 to 6 months, and then, for 1, 2 and 3 years following device implantation (by FDA guidelines) with variable requirements for echocardiograms, chest x-rays and electrocardiograms.

Certainly this technology is not for everyone. However, if patients are properly selected, the results of device closure of the atrial septal defect may prove to be, in many cases, equivalent to those results obtained through standard surgical intervention without some of the issues involved with open heart surgery.

In summary, atrial septal defects are relatively common congenital cardiac defects which are readily corrected through a number of surgical approaches, and a closely defined subgroup of patients may be managed by transcatheter closure. Regardless of the mode of closure, these defects are successfully closed with very low associated mortality and morbidity. Each mode of ASD closure has it's own associated risks and benefits, and a comprehensive treatment plan should include input from the primary care provider, the pediatric cardiologist and the pediatric cardiovascular surgeon.

Your feedback is very important! Please e-mail us with any questions or comments about this article.