Research

Adapting the Ozaki procedure for pediatric valve repair

Surgeons at Boston Children’s Hospital are the first in the world to use the Ozaki procedure, a technique for repairing the aortic valve in pediatric patients.

“Historically, there hasn’t been a great option for pediatric aortic valve repair,” says Christopher Baird, MD, director of the Congenital Heart Valve Program. “We’ve had some aortic valve reconstructive procedures that have worked and then you give them a year or two or three and you’re often re-operating.”

Because of this, most centers have opted to replace the valves with bioprosthetic or mechanical valves, both of which have limitations. Bioprosthetic valves can fail early and mechanical valves require lifelong anticoagulant therapy.

Looking for better long-term results

These limited options led Baird to take a look at a new technique for valve repair in adults developed by Shigeyuk Ozaki, PhD, in 2007.

“We thought we could apply this technique to children and have better, long-term results than the current techniques offered,” says Baird. “So we invited Professor Ozaki here in 2014 and he did the first two pediatric cases with me.”

Since then, Baird and his team have done about 30 cases with good results.

“We think this is clearly a better way to use a child’s own tissue to reconstruct the valve.”

The procedure uses custom sizers placed in the aortic root to determine the correct size for the leaflets. A template is used to draw the correctly-sized leaflet outline and suture guides on the pericardium. The surgeon then cuts the leaflets from the pericardium and sews them into the annulus to reconstruct the valve.

“It turns out we are the only heart center in the world doing this procedure on pediatric patients,” says Baird. “The company that manufactures the sizers, JOMDD of Japan, has asked us to be the trainers for the procedure.” Baird and Brenda Sefton, PA-C, have now trained other centers around the world, including those in Serbia, Georgia, Chile and Vietnam. They selected these centers very carefully, focusing on those that have higher volumes, which will likely lead to better outcomes.

Cardiology research Figure one: Using sizing apparatus to measure the annular distance between commissures. Figure two: Trimming the treated autologous pericardium using sizing template. Figure three: Evaluating the coaptation of three new leaflets under left ventricular negative pressure made by a left ventricular vent.

Improving the procedure through research

Although the procedure has had good results so far, Baird recognizes there is room for improvement. He recently teamed up with Peter Hammer, PhD, a researcher at Boston Children’s, to help further modify the procedure for pediatric patients.

“Peter is an engineer — he looks at the mechanics of things. His expertise is in simulation, so he’s going to take the procedure and help us analyze and simulate how those valves work and how we can optimize them in children,” says Baird. “We’re working with him to learn how we can take it to the next level.”

Hammer is confident he can help make some improvements. He uses simulation to examine all aspects of the procedure, bringing a quantitative angle to planning valve reconstructions.

“Professor Ozaki came up with adult templates based on lots of experimenting, but we’re not sure the pediatric ones are optimal or are the best size and shape to accommodate growth,” says Hammer. “Our goal is to see if we can make them larger, so they can accommodate growth, but without making them so big that they prolapse and don’t work in the short term.”

He’s also taking a closer look at the properties of the pericardium used to reconstruct the valves and how it might affect surgical outcomes.

“Ozaki was based on a fixed autologous pericardium, but sometimes we’re not able to use the child’s own pericardium, so we may also use fixed bovine pericardium,” says Hammer. He’s testing the properties of each, as well as how the amount of fixing affects the pericardium’s extensibility.

“If two surgeons treat the pericardium two different ways but use the same template to cut it, they’re going to get different results after the surgery,” explains Hammer. “To get the best results, we need to incorporate exactly what material they’re putting in and how it’s treated, and use that to help choose the size, and probably the shape too, as most of these tissues stretch more in one direction than the other.”

Hammer hopes his research will soon move from the lab into the operating room.

“We’re actually very close to being able to take a particular patient’s echo, make a model of the valve leaflet and run simulation. We’ll probably have some results in the next month or two,” says Hammer.

International registry closes the loop

Because this procedure is so new in the pediatric population, there is limited feedback regarding long-term outcomes. Baird is in the process of setting up an international registry to follow all the patients around the world who get this procedure. He and Hammer hope the registry will help further improve the procedure and outcomes over time, as it will give them more data from multiple centers from which to draw on.

“There are a lot of variables in this procedure,” says Hammer. “We can control certain things in a simulation and see how that affects outcome. But the international registry will help by increasing the data available from actual patients with the goal of expediting clinical understanding and the impact variables have on outcomes, ultimately improving care.”