Atrial Septal Defect (ASD)

What is the atrial Septum?

Atrial septum is the wall between right and left atria which keeps systemic return (blue blood without oxygen) and pulmonary return (red blood with oxygen) separate.

 

What is a defect in the atrial septum ?

Atrial septal defects represent a communication between the left and right atria.

 

Is there normally a “hole in the atrial septum” in the newborn ?

Usually there is a communication between the upper chambers called foramen ovale in the fetus. This is essential for the survival of the fetus. (See Fetal Circulation).

 

What happens to foramen Ovale ?

This has been discussed under PFO. Majority of the PFO’s close. Even if they dont, this is not considered abnormal in children and adults.

 

What are the types of ASD ?

We will consider three major types of atrial septal defects:

1.Secundum

2.Primum

3.Sinus venosus.

 

What is a secundum atrial septal defect ?

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).  This hole is usually relatively “central” in location. These are the holes which can be considered for device closure; many of them still will not be eligible for device closure. In comparison, the Primum and Sinuns Venosus cannot even be considered for this option and have only a surgical option available, which is a very good option.

 

What are Primum ASD’s ?

Primum atrial septal defects are part of the spectrum of the AV canals: a type of VSD (ventricular septal defect) , and are frequently associated with a split in the leaflet of the valve, or so called cleft mitral valve.

 

What are Sinus Venosus ASD’s ?

The sinus venosus atrial septal defect occurs at the junction of the superior vena cava and the right atrium. This represents the roof of the right atrium where blood returns from the upper extremities and head to enter the right atrium. These may frequently be associated with abnormal 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 mixing the red blood with blue blood. The cardiologist and the cardiac surgeon have to watch out especially for this abnormality.

 

How does ASD present ?

The majority of patients have few symptoms. However fatigue and shortness of breath are the most common complaints. In addition, the child may be way behind the typical weight of children in his/her age.

Why did it take so long for the ASD to be picked up ?

One of the most aggravating issues with parents whose children get diagnosed with ASD is: why so late when my child was born with it ? Well, these are difficult lesions to pick up. They hardly produce any symptoms, the child is otherwise healthy and the abnormality produces only a soft murmur which can be difficult to pick up. So, i think it is important to put the past behind; it is important to be still in the treatable group of patients; some of those picked up late (usually in adulthood) cannot be treated at all!

What tests are done to diagnose ASD ?

The diagnosis is confirmed by echocardiography, which will 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. It is obviously the mode of closure when device closure is planned.

How is ASD Closed ?

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. Open heart surgery is indicated for patients with these types of ASD’s. Indications for surgical repair of an atrial septal defect are right ventricular overload (due to flow from the left atrium into the right atrium) and elective closure prior to a child starting school.

What is Device Closure of ASD ?

This technique involves implantation of a 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. Defects amenable to such device therapy tend to be smaller (less than 20 to 25 mm though much larger ones have been closed by the author (upto 40 mm device implanted). 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.

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 ( up per collecting chambers).

Within six to eight weeks, the device acts as 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 entire procedure is usually 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).

How is it different from the Surgical ASD Closure ?

The 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.

Courtesy of: Interventional Pediatric Cardiac Treatment