Innovative device to treat mitral regurgitation
Dr Georg Daniel Duerr
Cardiac surgeons at the University of Bonn have invented a new device for treating mitral regurgitation, which they hope could save lives in the future.
Mitral regurgitation is a common form of heart disease among elderly patients suffering from ischemic cardiomyopathy, where the heart muscle doesn’t work as well as it should. The mitral valve in the heart separates the upper left heart atrium and the lower left heart ventricle - it opens to let blood flow from the left atrium and closes once the left ventricle is full of blood. In cases of mitral regurgitation, the valve doesn’t close shut properly and blood flows back into the left atrium. The patient may experience shortness of breath, tiredness and chest pain, and ultimately the result, if untreated, can be heart failure and death.
The current standard treatment to fix mitral regurgitation is surgery to implant an annuloplasty ring, a device which stops the leakage of blood back into the left atrium. But this surgery fails in some patients - moderate or severe mitral regurgitation returns in nearly 30 percent of patients within one year after undergoing annuloplasty.
A “redo” operation involving a second annuloplasty or mitral valve replacement is associated with significant mortality rates. Over recent years a new option has been developed - to implant a replacement valve known as a transcatheter heart valve (THV or TAVI) into the annuloplasty ring. This is a less invasive procedure performed by catheterization, threading the valve through one of the body’s arteries and opening it in the right place within the annuloplasty ring using a dilatation balloon.
THE BEST WAY TO MEET THE DEMANDS FOR VALVE-IN-RING IMPLANTATION WAS TO BREAK THE STRUCTURE OF THE OVAL DEVICE, TO MAKE IT ROUND.Dr Georg Daniel Duerr
But even this procedure has its problems. Transcatheter heart valves, when expanded in position in the heart, are circular, while the mitral annuloplasty ring already in place is oval, to fit the geometry of the body’s mitral valve. This mismatch of shapes means the intended seal is not tight, and mitral regurgitation can still occur. And as the THV cannot expand within a narrow oval shape to its optimal diameter, the blood cannot flow through the heart as easily as it should.
Now cardiac surgeons at Bonn University’s Heart Center have designed a new expandable mitral annuloplasty ring which is tailored to match a THV perfectly if one needs to be implanted at a later date.
Dr Georg Daniel Duerr and colleagues have experimented with an annuloplasty ring to create a different shape. Dr Duerr explains: “I first got the idea of searching for a new annuloplasty ring design when we treated a patient with recurrent mitral regurgitation due to a failing annuloplasty. We implanted a THV within the oval, pre-existing ring, and the result was far from perfect. We were able to downgrade the regurgitation, but the patient still suffered from shortness of breath and leg oedema. So I wondered why one could not change the structure of the ring.”
He and his fellow surgeons introduced four “breaking points” around the ring and placed a very thin steel “limitation cord” within the ring’s suturing cuff. The doctors were then able to implant a THV perfectly by breaking the annuloplasty ring at the breaking points so that it became circular rather than oval. The limitation cord acted as an anchor for the THV, so that the annuloplasty ring did not expand too much and the THV was firmly held in place.
This prototype was used in an experiment with a pig’s heart from a cadaver in 2015, and fluoroscopy showed it worked perfectly. “There was no leak anymore,” says Dr Duerr. “The best way to meet the demands for valve-in-ring implantation was to break the structure of the oval device, to make it round.”
So far this research - written up in 2015 and published in 2016 - is highly experimental and there have been no human studies. But annuloplasty rings of the future, the research shows, could be redesigned so that they accommodate THVs better.
Dr Duerr explains: “A round ring cannot be implanted, as the native geometry of the mitral valve is not round, but oval and three-dimensional. Therefore an annuloplasty ring must be oval and 3D in order to support the geometry of the native valve and ensure functionality. Only when it comes to THV implantation within the ring for a case of recurrent regurgitation should the ring adopt the configuration and form of the round THV.” In other words, the solution is an oval annuloplasty ring which can break and expand into a circular shape during any later procedure to implant a THV.