The role of 3D printing in interventional cardiology continues to evolve. A new study presented at the 2018 Society for Cardiovascular Angiography and Interventions (SCAI) Scientific Sessions finds 3D printing offers promise in the identification and prevention of paravalvular leaks (PVL)s following transcatheter aortic valve implantation (TAVR) (1).
Aortic stenosis (AS) is the most common heart valve disease worldwide and affects 25% of people over the age of 65 (2). Progressive valve calcification as part of the aging process is the most frequent cause in first world countries, followed by congenital alterations, such as bicuspid leaflets, and rheumatic disease (3). Calcium deposition within the aortic valve causes the valve to become thicker and stiffer. This prevents the valve from opening and closing properly, resulting in lower blood supply to the body, bringing on symptoms such as shortness of breath, chest pain, fatigue and fainting.
For years the standard treatment has been to replace the valve during open heart surgery. But a newer minimally invasive procedure, TAVR, approved by the FDA in 2011, uses a catheter to place a new heart valve. Instead of opening the chest and removing and replacing the old valve, the TAVR procedure involves folding up a new valve, slipping it into a catheter, inserting the catheter through a blood vessel in the leg -- then threading it up to the heart where it is opened like an umbrella, pushing aside the old valve and wedging the new one in its place.
Intermediate, high-risk, and inoperable patients with severe narrowing of the aortic valve are candidates for the TAVR procedure. While TAVR offers a less invasive alternative and shorter recovery time for patients who are too frail or sick to undergo open heart surgery, the procedure has its limits. Patients who undergo TAVR experience a higher risk of PVL around the new valve compared to those undergoing surgical aortic valve replacement. PVLs affect 26% to 67% of patients, and are associated with a higher mortality (4, 5, 6, 7). To address this complication, clinicians are looking for ways to find and prevent the leaks.
A PVL following TARV is often the result of an ill-fitting valve causing blood to flow around the prosthetic, instead of through it. If the right prosthetic is used from the get-go, this complication can be avoided and patient outcomes improved. However, without direct access to the patient’s heart, the complex anatomy of the aorta where it attaches to the heart and the irregular pattern of calcium deposits on the valve can make it difficult to size the valve and predict how the new valve will fit once in place. As Sergey Gurevich, M.D., a cardiovascular fellow at the University of Minnesota, said in a recent interview, “It would be nice to know what to expect before we go in, to help us with valve selection.”
To that end, he and his colleagues conducted a small, retrospective study of six patients who developed PVL after TAVR for severe, calcific aortic stenosis. The researchers analyzed pre-procedure CT images to create 3D printed models of each patient’s aortic root. They then “implanted” each of those models with the aortic valve device the patient received—all Sapien XT (Edwards Lifesciences). Five patients received the 26-mm valve, and one received a 23-mm valve.
The implanted 3D models were then rescanned with CT, and these images were compared with echocardiograms from the patients taken after TAVR. In every case, the implanted 3D models showed the same leaks that were evident on post-TAVR echocardiograms, suggesting PVL could have been prevented all together by using 3D patient-specific models for pre-surgical planning. In most cases, significant calcifications identified on pre-TAVR CT were associated with areas of poor stent apposition. Two patients found to have central aortic insufficiency were suspected to have patient-prosthesis mismatch.
When asked what the implications of the study were, lead author Sergey Gurevich, M.D. replied, “3D printing pre-procedure can identify those patients at risk for PVL, which can assist in the selection of the right valve size and valve type for that particular patient.” In a recent press release, he concludes, “We are very encouraged to see such positive outcomes for the feasibility of 3D printing in patients with heart valve disease. These patients are at a high risk of developing a leak after TAVR, and anything we can do to identify and prevent these leaks from happening is certainly helpful.”
The use of 3D models to improve the outcome of TAVR does not end there. Physicians and biomedical engineers at The Ohio State University are exploiting 3D printing technology to help select the optimal valve for patients receiving an aortic valve replacement and shared their experiences at the 2018 Cardiovascular Research Technologies conference in March. Using CT scans to model the patient's aorta, they create a 3D printed patient-specific model and used it to predict potential complications - such as leaks, blockages or blood clots - so that they can be avoided
"Using a simulator in a lab, we can replicate what happens in a patient's left ventricle," explained Prasad Dasi, a biomedical engineer at Ohio State University College of Engineering. Dasi's team precisely reconstructs a patient's aorta by 3D printing it using flexible materials that mimic the aorta. They then load the model into a heart simulator that pumps transparent, simulated blood through the system, and measures blood flow velocity and vortex patterns with and without a replacement valve.
"We can model various therapies, positions and types of valves to better understand problems such as leakage, clotting or coronary obstruction," Dasi explained. "We can observe how different valves not only relieve the stenosis but also minimize the likelihood of blood clots forming, which is the goal of the treatment."
“We currently have two valves to choose from in the transcatheter world. I suspect we will have at least four within two years," said Scott Lilly, interventional cardiologist and co-director of the structural heart program at Ohio State Ross Heart Hospital.
“Each valve is a little different, and the anatomy of every patient is unique. The ability to predict the function of the valve after placement, and which valve may work best with the least amount of leak and without impinging on adjacent structures is critical."
"For most patients, available valves work comparably. However, in some cases the anatomy of the patient may create additional considerations. For example, the patient may have calcified nodules on the valve leaflets, or coronary arteries that arise in close proximity to the valve," said Scott Lilly, M.D. "In some cases, for example, the coronary arteries come adjacent to where the valve would be placed," he explained. "Using 3D modelling we can determine whether or not to protect these blood vessels during deployment, or even whether to proceed with valve replacement at all. These discussions have directly determined how we approach many valve replacement procedures."
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