New stent procedures in children reduce LOS

Research shows success with treating PA stenosis

Coronary artery stenting has been used since the 1980s to help overcome vessel closure and restenosis following percutaneous transluminal coronary angioplasty. But did you know that stents can be used safely and effectively to relieve superior vena cava or innominate vein obstructions and pulmonary artery (PA) stenosis in children? The new procedures significantly reduce length of stay (LOS) for patients because they usually require only an overnight stay instead of major surgery. (For more on stents used to relieve occluded coronary arteries, see Hospital Case Management, November 1996, pp. 167-170.)

Frank Ing, MD, assistant professor at Baylor College of Medicine in Houston, recently presented several studies on new uses for coronary stents that are proving promising in children.1 He predicts that one use in particular is up-and-coming stent dilation of the superior vena cava (SVC) or innominate vein to allow transvenous pacing lead implantation in patients.

"If children or adults have an abnormal heart rhythm, the surgeon has to put a pacemaker in," says Ing. "The surgeon has to put the pacing lead from underneath the diaphragm coming up, and that’s an operation. Now we have ways to do it through the veins so you don’t have to have an operation. We actually put the lead through one of the veins and have it follow the blood vessel into the heart."

What about clotting problem?

The problem with the procedure is that sometimes the blood vessel through which the lead travels becomes clotted. By using a stent, surgeons now can open that occlusion and put the pacing lead back in to keep the pacemaker working.

"By doing that, we’re avoiding an operation to put the pacemaker in," Ing explains. "We can do this in the cath lab. This saves a lot of hospital time and pain and misery for the patient."

In a study conducted from May 1993 until January 1996, eight pediatric patients with either d-transposition of the great arteries with sick sinus syndrome or congenital/acquired complete atrioventricular block underwent transvenous pacing lead (TPL) implantation or replacement. All patients had significant SVC or innominate vein obstruction. Using intravascular stents, Ing and colleagues used a combined interventional and electrophysiological approach to open the obstructed veins and permit implantation of the TPL.

Two patients had complete SVC occlusion requiring a puncture through the obstruction with a transseptal needle. Ing says vessel patency was obtained with balloon dilation and stent implantation in those patients.

The other six patients had severe venous obstruction with a mean minimal vessel diameter of 3.1 mm. The mean pressure gradient across the obstructed vein before stent placement was 8.6 mm/Hg; after a Palmaz stent was placed in all eight patients, the mean pressure gradient across the stented vessels dropped to 1.0 mm/Hg and the mean diameter of the vessels increased to 14.2 mm. In six to eight weeks after the procedure, a TPL was successfully implanted through the stent.

A second study of pulmonary artery (PA) stents to treat PA stenosis in children with congenital heart disease evaluated the effect of stent implantation on the patency of adjacent segmental pulmonary arteries, says Ing. Typically, those children had to undergo open-heart surgery to correct the problem, says Ing, but the stents are being used routinely at Baylor instead.

"The true benefit of this is that it’s an alternative to surgery," he says.

Risk factors identified

In the first 100 PA stent procedures done at the Texas Children’s Hospital in Houston, Ing and colleagues identified the risk factors for branch vessel occlusion with the procedure. (Ing refers to branch vessels as "side branches.") Of 41 stents in 34 patients that were placed across 62 branch vessels, 49 (79%) of branch vessels remained patent after stent placement, and 13 (21%) were occluded. The factors most often associated with vessel occlusion were small vessel diameter, severe stenosis of the stented vessel, small patient body surface area, and acute angle of origin from the stented vessel.

"The side branches do not commonly occlude with stenting," he says. "It’s not as prevalent as we might have anticipated. But the smaller the orifice of that side branch, the more acute of an angle that side branch forms with the main branch, especially in smaller patients."

In those patients, Ing says he must determine if it’s worth the sacrifice in that side branch to obtain better blood flow to other parts of the lung. Because smaller children have smaller vessels, he says the procedure can only be done on children weighing 12 kg or greater. It requires a two-day length of stay with no routine admission to the intensive care unit. Patients require no medication on discharge other than persantine to prevent blood clots.

In another study, Ing tested an "open-ring" stent for pulmonary arteries that is meant to expand as the child grows so the child doesn’t have to undergo repeated surgeries.3 That study was undertaken in animals and will be expanded to human trials soon, says Ing.

References

1. Ing FF, Mullins CE, Grifka RG, et al. Stent dilation of superior vena cava/innominate vein obstructions permits transvenous pacing lead implementation. Abstract #3950. Presented at the American Heart Association 69th Scientific Sessions, New Orleans; November 1996.

2. McMahon WS, Mullins CE, Grifka RG, et al. Fate of pulmonary artery branch vessels with intravascular stents. Abstract #0324.

3. Ing FF, Fagan TE, Kearney DL, et al. A new ‘open-ring’ stent. Abstract #0323.