Atrial septal defect
The atrial septum is the wall of tissue and muscle between the upper two chambers (atria) of the heart. An atrial septal defect is a hole in this wall.
A hole or defect like this allows both upper chambers of the heart to communicate and permits an abnormal flow of blood from one chamber to the other.
As a consequence of this, there is mixing of the oxygenated and de-oxygenated streams of blood that are usually kept separate.
This type of heart problem is commonly an isolated finding but can occur together with more complex heart disease where its presence may be beneficial- by providing a site of mixing.
Types of ASD
Atrial septal defects (ASD) are classified into differing types dependant upon their geometric position in the atrial wall.
Central defects of the atrial wall
(Secundum defects). This is the most common type of ASD. An atrial communication in the middle part of the atrial septum is a normal finding before birth and when covered by a small flap is called the ‘foramen ovale’. If the hole remains after birth it is called a patent formane ovale or PFO.
Low defects of the atrial wall (Primum ASD)
This type of atrial septal defect occurs together with an abnormality of the one-way-valve between the upper and lower left heart. It can also be part of a more complex type of heart problem called an atrioventricular septal defect (AVSD).
High defects of the atrial wall (sinus venosus)
This type of ASD can be difficult to visualise and is commonly seen in an association with an abnormal position of the right upper pulmonary vein (one of the blood vessels bringing back oxygenated blood back to the heart).
A baby or child with an atrial septal defect may be asymptomatic or have mild symptoms only. As this type of defect can cause extra blood to flow to the lungs, this may result in inefficiency between lung blood flow and oxygenation and result in an increased frequency of chest infections.
Large defects can cause extra strain on the heart causing dilatation (stretch) of the right hand-side of the heart. Babies with large defects may be breathless and feed poorly. Failure to thrive (poor weight gain) and reduced exercise tolerance are sometimes observed in older children.
The extra flow of blood to the lungs usually produces heart murmurs in children (an abnormal heart sound) that be detected on routine health checks and this is a common reason for referral.
Large defects that produces symptoms or structural changes in the heart usually warrant surgical or key-hole (catheter based) closure to alleviate the symptoms and protect against problems that may develop as a consequence in young adulthood.
Presentations
Investigations
A paediatric cardiologist (baby or child's heart doctor) can make this diagnosis with echocardiography.
They are able to visualise the atrial wall, and assess any abnormal flow across the defect. The haemodynamic effects on the other cardiac structures are also quantified together with the overall performance of the heart and circulation.
An electrocardiogram (ECG) may be performed to assess for the electrical pattern of the heart and to look for dilatation of the right-sided cardiac structures.
Treatments
a) Medical follow-up alone
Encouragingly, small central atrial defects or PFO’s close spontaneously. This may take several years to occur and only require periodic medical supervision in an outpatient capacity
b) Key-hole closure (catheterisation)
Also know as a ASD device closure. If the central defect is not too big and surrounded by good margins of tissue - a key hole procedure (cardiac catheterisation) may be used to close this type of hole.
This is usually undertaken as a day-case procedure. A short anaesthetic is given, after which a cannula (or drip) is sited into the blood vessel in the groin. A thin tube (catheter) is then advanced into the leg and then towards and into the heart using special x-rays. Once suitability for device closure is once again confirmed, the device is deployed across the hole, thereby occluding it. The procedure lasts approximately 2hrs and patients are discharged home the same day. The device remains sited in the heart and becomes completely incorporated into it.
Surgery
Cardiac surgery - Large central defects, other types of ASD or haemodynamically important holes in small children require open-heart surgery for repair. The type of operation depends upon the position of the defect and any associated lesions. This type of child heart surgery is the most straightforward type of operation that our surgeons perform and we see that over 98% of patients come through the operation without long-term difficult or problem.
Follow up
The long-term outlook for central types of ASD is very good irrespective of the strategy used to close the hole (catheter device closure or cardiac surgery). Further surgical or catheter procedures are not usually required and children lead normal healthy lives. For those with low defects of the atrial wall (primum defects) - patients require medical follow up as an outpatient, to observe for problems with the associated abnormal left sided atrioventricular heart valve that may necessitate additional surgical procedures.
