Aortic valve replacement: Precise preoperative surgical preparation thanks to a silicone heart

Interview with Prof Stephan Ensminger, senior physician at Clinic for Thoracic and Cardiovascular Surgery, Heart and Diabetes Center NRW

An 80-year-old female patient needs a new aortic valve replacement. Since the old one is severally calcified, the leaflets no longer open properly. Due to various factors, the patient is considered inoperable. Nevertheless, to make surgery possible for her, specialists at the Heart and Diabetes Center NRW in Germany have prepared the intervention based on an exact 3D heart replica.

23/02/2015

Photo: Stephan Ensminger

Prof. Stephan Ensminger; © Armin Kühn/HDZ

Aside from conducting this research, Professor Stephan Ensminger, senior physician at the Clinic for Thoracic and Cardiovascular Surgery, also personally performed the surgery. MEDICA.de spoke with him about the reasons behind this intensive surgery preparation and its use in clinical application.

Professor Ensminger, how did you come up with the idea to first test the surgical procedure as well as the replacement on a model?

Stephan Ensminger:
The primary motivation for our idea was to minimize the risk for this particular patient and to maximize our chances of success, since this patient is older, very ill, has already undergone prior surgery and this specific surgery had not been done prior to this. The basic idea was to develop an individual algorithm for a patient and to identify all risks due to difficult preconditions beforehand.

The innovation of the current study consists of exactly recreating portions of the patient’s heart out of silicone for a patient with a defective prosthetic aortic valve and thus simulate the crucial surgical steps beforehand. To do this, we molded the left ventricle, the outflow tract and the aorta with the coronary outflow tracts and inserted the biological prosthetic valve the patient already has into the silicone model, thereby creating an exact copy of the patient’s heart. Subsequently another aortic valve replacement was attached in this model. We then checked its function with the help of different tests before the patient had surgery.

Why were tests needed beforehand?

Ensminger:
This was a patient, who had already received an aortic valve replacement. This valve degenerated within three years and needed to be replaced. Based on the advanced age of the patient, her previous illnesses and the prior surgery, another open-heart surgery put the patient at a very high risk; she was actually considered inoperable. In addition, we had to decide ahead of time which type of catheter valve was best suited for implantation into the degenerated aortic valve replacement and therefore tested several catheter valves in the 3D model.

How was the silicone heart made?

Ensminger:
The heart and the large blood vessels were examined via computed tomography. We printed an exact 3D model made of silicone based on this data. The damaged prosthetic heart valve was also implanted into the model. In doing so, we had an exact copy of the patient’s heart.
Photo: Aortic valve replacement in detail

The new valve is inserted via catheter into the heart. Once in the heart, the valve replacement has to be placed exactly in the area where the calcified valve of the patient is located; © Armin Kühn/HDZ

What functional tests were subsequently performed?

Ensminger:
In collaboration with the RWTH Aachen University- Helmholtz Institute, we mounted the silicon model into a perfusion device on location. In doing so, we performed the functional tests, that is to say we checked all technical aspects that were required for a successful surgery. We wanted to measure ahead of time whether the gradient is accurate and whether it is technically feasible for the valve to be positioned correctly. On the other hand, we wanted to find out at what height we needed to position the new valve to achieve a good gradient. Of course, the valve was also intended to be tight.

Then we positioned different valves by different manufacturers on the defective prosthetic and perfused everything to find the proper prosthetic valve. That was important, because the patient is of short stature and the valve therefore needed to be very small. We needed to particularly determine the right height where the new valve was to be anchored in the old valve. The opening that occurs when two valves are positioned on top of each other is rather small; the pressure gradient between the left ventricle and the aorta would subsequently be large and the patient would not see any clinical pathology improvement under these circumstances.

The leaflet movements of the potential new valve were assessed with a high-speed camera and we examined how both leaflets interact with each other. This was crucial, since there could be problems in terms of durability and the opening, if the old valve leaflets cannot be completely pressed against the wall or the old leaflet hits against the new one. The model was then X-rayed to determine the exact position of the new heart valve in the old one for the surgery. Thanks to our tests prior to the surgery, we were able to determine the optimal position of the catheter heart valve in the defective aortic valve replacement for our patient; the new valve leaflets now work perfectly.
Photo: Ensminger and Gummert holding a 3D heart replica

Professor Stephan Ensminger and Professor Jan Gummert (director at the Clinic for Thoracic and Cardiovascular Surgery) with 3D heart replica; © Armin Kühn/HDZ

What did you find out during all this?

Ensminger:
The primary goal of the tests was to determine the best heart valve as well as the optimal position for anchoring it. It turned out that the first position I would have intuitively chosen based on my interventional experience was the inferior alternative. Given this result, those were very important findings and we chose the second position. The gradient across the aortic valve replacement in the 3D model was between five and ten mmHg, which was an excellent result.

How was the surgery?

Ensminger:
The X-ray pattern of the planned valve position was projected onto a monitor during the surgery. I then transferred this result onto the patient’s heart and positioned the valve accordingly, which was at a relatively high position in the old valve based on my intuition. Without the results from the 3D model, I would not have implemented things this way, but the result was perfect. The gradient across the new aortic valve replacement was actually too perfect; it was even lower than in the 3D model. This is when we conducted follow-up exams in the laboratory using the same 3D model. The degenerated prosthetic valve was made of Nitinol, a self-expanding material. The only difference was that we stretched the implanted valve once more during the surgery after we had positioned it. We found out in the laboratory that by doing so we actually also expanded the ‘old valve‘, because the Nitinol stent of this prosthetic valve softened. This is why the opening of the prosthetic valve also widened and the results were even more impressive.

To what extent is this precise preoperative surgical preparation suited for clinical application?

Ensminger:
Time and cost expenditure is not as high as first assumed. However, it is by no means necessary to apply this procedure for every transcatheter aortic valve replacement. In our case, we were dealing with a high-risk patient and a technically difficult procedure that was performed for the first time. According to the manufacturer, the degenerated prosthetic heart valve was not suitable for this kind of procedure. This is why the developed algorithm made it possible to plan this new intervention in detail before the surgery and thus reduce the surgery risk and increase patient safety. Of course, this is also possible for other new interventions.

You have subsequently applied this procedure several times already.

Ensminger:
When you plan a new catheter intervention where the risks and the procedural success cannot be assessed beforehand, creating a good algorithm is essential and surgical success should be repeatable. We already operated on a second patient, who is 93 years old. She was also able to leave the hospital one week after the surgery. Both patients are doing very well. To us it was and remains important to make patient safety the focus of preoperative preparations for these types of new procedures and to achieve the best possible result for the patient.
Foto: Melanie Günther; Copyright: B. Frommann

© B. Frommann

The interview was conducted by Melanie Günther and translated from German by Elena O'Meara. 
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