Interventional Techniques to Treat Congenital Heart Disease
Congenital heart disease has been traditionally treated with surgery; however, with the development of interventional cardiology, patients are now benefiting from minimally invasive techniques.
Traditionally, open-heart surgery was performed to treat congenital stenoses and perform device closures for septal defects and other vascular structures in all patients, including newborns. However, remarkable advances have meant that, now, the technique used for the majority of congenital heart problems is almost always exclusively interventional. A standard transcatheter procedure using a closure device mounted on a balloon catheter is performed to close defects, while a balloon dilatation procedure is carried out to dilate the obstruction during cardiac catheterization to treat stenosis. The advantage is that these techniques can be carried out either as outpatient procedures, a one-day admission to hospital or in newborns, shortly after birth. The interventional procedure is carried out with a beating heart and patients frequently go home the next day with no recovery period, as opposed to surgery, where a hospital stay of several days is required.
This article will focus on the interventional closure techniques for septal defects and other vascular structures.
Patent Ductus Arteriosus and Atrial Septal Defects
The ductus arteriosus is a fetal blood vessel connecting the aorta with the pulmonary artery.This vessel usually closes in the first days of life, however, if it remains open, this abnormal connection is called patent ductus arteriosus (PDA).Traditionally, the treatment was cardiac surgery, but currently around 98% of all PDAs are closed using the catheter technique, by inserting a device into the blood vessel through a catheter to close it.
The atrial septal defect (ASD) is a hole in the atrial septum that allows a portion of blood returning to the left atrium to pass to the right atrium, right ventricle and pulmonary arteries, placing additional pressure on these heart structures as well as the lungs. Eight per cent of all ASDs are now closed interventionally by the implantation of a permanent device through a catheter that remains and eventually becomes part of the heart wall. As with the other interventional procedures, the ease of implantation, very high success rates matching surgery with minimal morbidity has made ASD closure an ambulatory procedure, suitable for patients of all ages, from one-month-old babies to those 80 years of age.
Currently only secundum ASDs are amenable to non-surgical closure, meaning that there are still some cases that cannot be treated using transcatheter techniques. Occasionally, an ASD is in a very unusual location or is unusually large and the risk of the catheter procedure is too great. In these circumstances, the surgical option would be chosen, although with advances in techniques and devices, these occurrences are decreasing.
Ventricular Septal Defects
New interventional techniques have been developed in the last few years to close ventricular septal defects (VSDs), holes between the ventricles of the heart, with implantable devices. However, these techniques are not as advanced as those for the closure of PDAs and ASDs, and currently there are no US Food and Drug Administration (FDA)-approved closure devices. The techniques are, however, performed extensively in Europe and are under investigation in the US. Overall, interventional procedures are just as effective or more effective or just as safe or safer than surgery. However, if performing an interventional technique would be less safe than surgery, then the patient would obviously receive surgery.
Limitations of Interventional Treatment of Congenital Heart Disease
The biggest limitation is access, as most procedures are carried out on very small children, and therefore only a limited size of blood vessel is available to introduce the catheters. In addition, the arteries are usually quite small, and so the risk of damaging the artery remains. It is possible that while repairing the heart, the artery or the vein in the leg may become damaged. Industry has responded to this problem by miniaturizing the delivery systems, thus minimising the risk to the patient. Although the risk has not been completely eliminated, the situation is being continuously reviewed and investigated, and the risk is further being decreased.
New Investigational Areas in Interventional Cardiology
Valves are now being replaced percutaneously in the catheterization laboratory, rather than in surgery, although this is not yet a standard of care, as investigations are still being carried out. However, in the near future, this technique will be a standard of care in Europe for replacing of the pulmonary valve and in the US, the FDA is working with interventionalists to start an investigational protocol to replace artificial pulmonary valves in the catheterization laboratory without the need for open heart surgery.
In congenital heart defects the procedure is always carried out using balloon mounted stents and devices, thus much of the instrumentation used consists of balloons and stents mounted on balloons.
The stents that are utilized to treat congenital heart defects differ from the adult coronary stents, which are designed for use in large vessels. As congenital stents are placed in the vessels of small children, they need to have enlarging properties. The stents used must have the ability to be enlarged on one or two occasions in the future, up to seven years later. While closure devices provide the instrumentation for ASD and PDA closure procedures.
Future of Congenital Heart Defect Treatment
More biodegradable devices will be available in the near future that will allow the normal heart to grow, encompass, and re-absorb these devices. This is a development that is predicted to appear on the market in around five years time.
In addition, while currently X-ray imaging and ultrasound are employed to assist the procedures, in the future the ability to deliver these devices under realtime imaging, such as magnetic resonance imaging (MRI) will exist. This will ensure that the patient is exposed to minimal radiation, one of the limitations of these current interventional procedures. Although, currently for various reasons it is not possible to use the MRI, again, these changes will occur in the next five years.
Finally, in the future there will be more of a cooperative effort between the surgeons and interventional cardiologists to perform hybrid procedures, where the surgeon and interventionalist are working together in the same room to deliver respite for the patient in the most efficient, and accurate way. The goal is to build hybrid rooms where both the surgeon and the cardiologist can work easily together.