Growing Hearts, Evolving Technologies

In recent decades, the role of cardiac catheterization in pediatric cardiology has evolved from being a primarily diagnostic modality into a mainstay of interventional treatment.

With the emergence of less invasive imaging technologies such as MRI, CT scans and echocardiographic imaging, there has been decreased reliance in cardiac catheterization for diagnostic imaging. This overall momentum toward less invasive options has, in turn, shifted transcatheter technology into a new status — alternative and adjunctive therapy to open-heart surgery.

“What we’re seeing over the last several decades, and what we’ll continue to see in the future, is a shift away from cardiac catheterization as primarily a diagnostic procedure,” said Dennis W. Kim, MD, PhD, a pediatric cardiologist at Sibley Heart Center Cardiology – Children’s Healthcare of Atlanta at Emory University. “We’re using catheter-based strategies now less from a diagnostic perspective and more from an interventional treatment perspective.”

The use of transcatheter approaches in young children, however, presents its own unique challenges.

“The field of catheter intervention for congenital heart disease is, in many ways, exceptionally more complex than catheter intervention for adult-acquired disease,” said Larry A. Latson, MD, FAACP, FACC, FSCAI, director of pediatric interventional cardiology at Joe DiMaggio Children’s Hospital in Hollywood, Fla. “There’s a limited size range that adult cardiologists have to deal with, and a relatively limited number of lesions, whereas with congenital heart disease, we go all the way from the fetus to adult-sized patients, and the range of malformations we see is almost infinite.”

Expanded Indications

Latson said prior to the early 1980s, balloon atrial septostomy was the only widely utilized pediatric catheter intervention.

“Now, we routinely treat a number of congenital valvular problems, such as valvular stenosis, septal defects and abnormal vascular connections, with catheter intervention approaches,” he said.

Kim said catheter approaches to atrial septal defect closure offer a viable alternative to surgery.

“With various transcatheter devices, the closure of atrial septal defects is now a realistic and reasonable therapy vs. an open-heart procedure,” he said. “There is generally just an overnight stay in the hospital, and the patient goes home the next day.”

Muscular ventricular septal defects may also be approachable through an occlusion device called the Amplatzer Muscular VSD Occluder (St. Jude Medical).

“The ones that are available here in the United States are specifically for use in muscular septal defects,” Kim said. “However, in Europe and Asia, devices are also available for defects of the membranous septum, which is the area that’s closer to the valves.”

Another significant innovation in congenital heart disease interventions is the ability to perform valve replacements through catheter-based mechanisms, Kim said.

“In some cases, we’re actually able to implant pulmonary valves without the need for surgery,” he said.

Catheters in PDA Correction

One of the more common indications for catheter-based procedures is closure of the patent ductus arteriosus (PDA).

“In the past, this was something that required surgical ligation,” Kim said. “But now we are able to close most of these with various embolization coils or specifically made devices.”

According to Richard E. Ringel, MD, associate professor of pediatric cardiology at Johns Hopkins Children’s Center, Baltimore, cardiac interventionalists may also need to use stents to open the ductus arteriosus in babies with hypoplastic left heart syndrome. This is performed as part of a “hybrid” procedure done collaboratively with a surgeon.

“Instead of undergoing open-heart surgery, the baby with hypoplastic left heart syndrome during the first week of life will be stabilized,” he said. “And part of that procedure requires stenting wide open the ductus arteriosus.”

Other Uses of Stents

Another common use of stents in the pediatric population is for coarctation of the aorta.

“Coarctation of the aorta is either native or postsurgical, meaning a scar has developed in the region of prior surgery and now has created a recurrence of the obstruction,” Ringel said. “This is one of the most common sites of stenting.”

Kim said angioplasty and stenting seem to especially benefit older children and adults with coarctation of the aorta.

“Either using balloon angioplasty to stretch that area open, or stenting, has been good primary therapy for coarctation of the aorta, with excellent long-term results,” he said.

Although coarctation of the aorta is usually corrected surgically in younger children, Kim said stenting and/or angioplasty may be considered after a recurrence.

“There is about a 10% to 15% chance of recurrence of coarctation after surgery, and so either balloon angioplasty or stenting may be considered afterward.”

Ringel said stents are also used in babies with cyanotic heart disease, who have inadequate or no blood flow into their pulmonary arteries.

“Instead of performing a modified Blalock shunt, the interventional cardiologist would put a stent into the ductus arteriosus to provide ongoing flow into the pulmonary arteries,” he said.

Less common uses of stents in children are for stenosis of the superior or inferior vena cava, injured iliac arteries or veins, or conduits that have become stenosed post-surgically, Ringel said.

A Quandary of Stenting

One of the more significant challenges in pediatric stenting, according to Latson, lies in balancing the need for a very small delivery system with the need for the stent to grow with the child.

“We’re dealing with defects that kids are born with, primarily, and most of the time, we’d like to get a stent in using a very small delivery system to place in a very tiny vessel in a newborn,” he said. “But if you place a very small stent that isn’t bulky and doesn’t grow, you’re going to have to go in and surgically redilate, or cut out that stent as the child gets bigger.”

Ringel said, as an interventional cardiologist, he strives to put in stents that are capable of expanding to larger sizes.

“We don’t want to take a little baby into the cath lab and put in a 4-mm diameter stent that can only get to be 5 mm, because within a year or two the child will outgrow it, and the surgeon is going to have to cut the stent open,” he said. “We’re in a bit of a quandary at times.”

The Impact of Stent Size

Ringel said for the pulmonary artery, he uses stents that can expand up to 18 mm in diameter, such as the Palmaz Genesis XD (Cordis), the IntraStent (ev3 Endovascular) or the Valeo Biliary Stent (Bard PV). For the aorta, Ringel said he would use a stent that dilates up to between 20 mm and 22 mm, such the IntraStent Maxi or the Palmaz XL.

“However, this does end up excluding some of the smaller children who might benefit greatly from stents,” he said. “We might not have a stent that is small enough to be put into place in a small child, yet be expandable to a big enough size. Or sometimes, we might have the stent, but it is too long for that small child.”

Particularly in pulmonary artery stenting for young children, a 16 mm or 19 mm long stent might overlap with one of the pulmonary artery branches or will stick too far out into the main pulmonary artery, Ringel said.

“Some doctors will trim the stent back or use a cutting balloon or high-pressure balloon technology instead of putting in the stent,” he said. “Or when we just can’t do anything else, we might take a medium-diameter stent that does come in a shorter length, knowing that in X number of years, this child will need to have surgery.”

Off-Label Use

Currently, Ringel said, the stents used for pulmonary artery interventions are all utilized off-label.

“There are no stents approved for pulmonary artery use, so we’re talking about biliary stents, some iliac stents, and when we talk about very small children, we might put in a cardiac stent,” he said. “So we’ll put in a stent 4 or 5 mm in size, knowing that we’ll never get that any bigger, and that something will need to be done in the future.”

When faced with this situation, Ringel said some cardiologists will rupture the stent in place and implant a new stent inside.

“That’s how desperate we’re getting in treating some of the very small babies who have pulmonary artery problems,” he said.

Hope for the Future

As transcatheter intervention technology continues to progress, cardiologists anticipate advances in stents for the very youngest cardiac patients. The Coarctation of the Aorta Stent Trial (COAST), led by Ringel, is investigating a new bare-metal stent for use in older children and adults with coarctation of the aorta.

“Another trial, COAST II, is looking at a covered stent, which has a wrapper around it. If something tears, the covering around the stent will seal up the leak,” Ringel said.

Both of these trials are currently in the process of data collection, he said.

“This would be the first stent approved for use in coarctation of the aorta,” he said.

Latson said studies are also under way to evaluate stents for use in small children.

“The benefits of catheter intervention have been very adequately proven, and because of those benefits, there’s a lot of pressure to extend the range of what we can do,” he said. “I see the field expanding to apply stents and closure devices to very small children, all the way to premature babies and even fetuses.”

Ringel said he eventually hopes to see the development of biodegradable stents or drug-eluting stents for the pediatric population.

“We’ve come a long way, but we remain hampered by the fact that we are using stents that were not designed for the location they’re going into, and therefore are not optimal for the patient and their anatomy,” he said. “We’re always hoping that the industry will eventually proceed with making stents that are either more flexible or easier to implant, so that babies can gain benefit from them without limiting their future potential.” – by Jennifer Byrne

Dennis W. Kim, MD, PhD, can be reached at Sibley Heart Center Cardiology, P.O. Box 941907, Atlanta, GA 31141; email: kimd@kidsheart.com

Larry A. Latson, MD, FAACP, FACC, FSCAI, can be reached at the Joe DiMaggio Children’s Hospital, 1150 N. 35th Ave, Suite 575, Hollywood, FL 33021; email: llatson@mhs.net.

Richard E. Ringel, MD, can be reached at Johns Hopkins Children’s Center, 1800 Orleans St., Baltimore, MD 21287; email: rringel@jhmi.edu.

Disclosure: Kim, Latson and Ringel report no relevant financial disclosures.