Marisa Benjamin 10/21/17
Research Project Final
Transcatheter Aortic Valve Replacement: Transfemoral Approach
This research paper will be discussing the topic of transcatheter aortic valve replacement (TAVR), specifically using the Edwards SAPIEN 3 transcatheter heart valve. Heart valve replacement is an extremely common procedure and according to the Texas Heart Institute12 surgeons perform 106,000 procedures in the US each year. There are many replacement options out there, with the most common being open heart surgery. Open-heart surgery can be extremely problematic and have serious complications such as stroke, myocardial infarction, and serious bleeding. There is a strict criterion for patients undergoing surgery and a high risk for patients that are fragile, elderly, oxygen dependent and could suffer from mortality. For these select patients, open-heart surgery is not an option and the transcatheter valve replacement via transfemoral or transapical route is used. These procedures are less invasive and performed on intermediate and high-risk patients. Patients using this approach at this level of risk are associated with a very low risk of mortality and complications. The idea is to one-day use the transfemoral or transapical approach on patients of any level of risk because it is less invasive then open-heart surgery.
Heart Structure Overview
To better understand this procedure, an overview of the structure and function of the heart valves is reviewed here. The heart consists of four different valves, aortic, tricuspid, pulmonary, and mitral. Although the aortic valve will be the valve in focus, the common function of all four is to provide unidirectional blood flow throughout the heart and blood vessels.
Figure 1. Diagram of the human heart. (10)
Shown in the figure above, the aortic valve is located in the lower left chamber and opens to allow blood to leave the heart from the left ventricle to the aorta and on to the rest of the body. The main function of the aortic valve is to receive oxygen-rich blood from the left ventricle and pump it through leaflets and on to the rest of the body. This valve consists of 3 leaflets in the shape of a peace sign and made up of thin fibrous walls. This is the mobile part of the valve. The leaflets open to allow blood flow during ventricular contraction and then close to prevent regurgitation. Healthy, working leaflets allow for unidirectional blood flow.
Figure 2. Leaflets located in the aortic valve. Tri-leaflet is normal and bicuspid is due to congenital heart defects.. Both valves would be candidates for replacement. (9)
Conditions Impacting the Aortic Ventricle
The aortic ventricle is extremely susceptible to conditions such as aortic stenosis and aortic regurgitation.(5) Stenosis is a condition where there is a narrowing of the aortic valve, which prevents the valve from opening fully. The effect of this is a shortage of blood flow throughout the heart muscle. There are multiple causes of stenosis including but not limited to congenital heart defects, infection, and degenerative conditions. Degenerative conditions such as aging cause stenosis in the result of calcium build up around the valve. The calcified leaflets of the valve that are normally flexible become stiff and thick, reducing blood flow. A common birth defect that causes stenosis is being born with a bicuspid aortic valve, shown above in Figure 2. Having two leaflets instead of three make the valve more susceptible to calcification. With increased calcification results in a more severe case of stenosis.
A degree score(1) is grading based on a set of criteria that influences clinical decision making regarding the severity of stenosis. The severity of stenosis can vary between mild, moderate, severe, and very severe. The two components of the degree score are mean gradients measured in mmHg and aortic valve area measured in cm2. Mild <25 mmHg, >1.5cm2, moderate 25-40 mmHg 1.0-1.5cm2, severe >40mmHg <1.0cm2, very severe >70mmHg <0.6cm2. (1) The sizing of the Edwards prosthesis depends on this scale, which will be discussed further in this paper. Aortic regurgitation is also a common condition of the valve. Regurgitation is leakage of the aortic valve each time the left ventricle relaxes. Leakage allows blood to flow backward from the aorta back into the left ventricle with relaxation. To compensate for leakage of blood, the heart has to work harder and pump faster which can result in heart failure.
TAVR (transcatheter aortic valve replacement) is one of the main and most effective therapies for the above valve conditions. Anderson and his colleagues implanted the first successful implantation in a pig model in 1992. (11). With modifications and advancements in technology, the first successful human implantation was performed on April 16th, 2002 on a fifty-seven-year-old male and the replacement was successful. . As of 2013 there have been 80,000 patients treated with TAVR with new generations of the prosthesis being designed every couple of years. (7) This procedure is designed for patients who are high risk for complications and death during open- heart surgery or are unable to undergo general anesthesia resulting from restrictions such as oxygen dependency. (4) Local and conscious sedation limits risk for complications during the procedure. For fragile and high-risk patients this is the best option because it is less invasive. So far most procedures are done on severe risk patients, but studies are being conducted with intermediate and low-risk patients as well. This supports the idea mentioned in the introduction, that less invasive procedures are better for patients of any level of risk.
Before the procedure, a number of measurements such as location and size of prosthesis, inflation of balloon volume, size of the catheter, and many more need to be taken to produce a procedure plan. Two and three-dimensional transesophageal echocardiography (TEE) is commonly performed at baseline, during, and after the procedure. TAVR can be conducted through numerous approaches, but the one in focus will be transfemoral. This approach uses the femoral artery as the delivery pathway for the new prosthesis. To begin the procedure, the patient is under local or conscious anesthesia and prepped. A small incision is made to access the artery. A sheath is inserted which allows the deflectable quadripolar balloon catheter to enter and be guided up to the aortic valve. With the correct positioning, the balloon is inflated and opens up the narrowed calcified valve. The balloon is then deflated and pulled back through the sheath. With the new prosthesis attached, the balloon is sent back through to the valve where fluid fills up and the prosthesis expands to the exact size of the newly opened damaged valve. The balloon is deflated once again and removed along with the sheath and catheter. With the new prosthesis held tightly in place, it begins to function immediately.(2)
Edwards SAPIEN 3 Prosthesis
Edwards Lifesciences being a leader in TAVR prosthesis developed in 1958, when Miles Edwards set out to build the first artificial heart.(11) Dr. Albert Starr suggested developing an artificial heart valve instead which was in higher demand, and the first prototypes were developed two years later. With an increase in growth of heart disease, there was also an increase in development of Edwards Lifesciences(6) production. This company has designed the Edwards SAPIEN, Edwards SAPIEN XT, and the Edwards SAPIEN 3, which is the latest model. The Edwards SAPIEN 3 is designed for optimal strength and durability. The goal of having this prosthesis implanted invasively is to reduce risk. This prosthesis needs to be of the highest quality so it does not have to be repeated in such high-risk patients.
Figure 3. Edwards SAPIEN implant. Shown tricuspid leaflets open and closed. (8)
The structure of the prosthesis has three main components that make it so efficient. The geometric design is four rows of four columned cells that are between each commissure providing increased strength. The columns are made with a cobalt chromium alloy frame. By using this material it ensures fatigue resistance and radial strength needed for circulation. Embedded in the frame is bovine pericardial tissue that is in the leaflet shape. This material is used because of its hemodynamics and extreme durability. The Carpentier-Edwards Thermafix is used for this design to reduce the risk of calcification of the new valve. The prosthesis also has an outer-skirt component that was designed to prevent paravalvular leak (PET). Because of the cardiac anatomy, this product is made with a low frame height. SAPIEN 3 is manufactured in three main sizes 23mm, 26mm, and 29mm. Based on the degree of stenosis (calculated by the mean gradient and aortic valve area), different sizes are able to fit a wide range of patients.
Figure 4. A bar graph shows the comparison on SAPIEN XT and SAPIEN 3(11)
A bar graph was used to show the difference in strength between the Edwards SAPIEN XT and the Edwards SAPIEN 3 model. Comparing the 23mm prosthesis, XT had an average radial strength of 1.3mm and the latest model had 1.4mm, 26mm prosthesis went from 1.1mm to 1.4mm and 29mm prosthesis went from 1.2mm to 1.3mm. (6) The strength of the replacement valve is very important because it will last longer and with stand ware and tear through the years. The patients who are receiving these valves through this approach are already at high risk for complications and to have to repeat this procedure can be very strenuous on them. The body accepts the foreign material as long as the patient is not allergic to nickel or cobalt.
One of the major case studies used to conduct research for this paper was Thirty-day outcomes in patients at intermediate risk for surgery(5). The objective of this study was to access the safety and efficacy of the Edwards SAPIEN 3 prosthesis. A total of one hundred and one patients with a mean age of 84.4 3.8 years with 45.5% being male, participated in TAVR using the transfemoral approach. There was a high exclusion criterion such as an occurrence of myocardial infarction within one month before procedure, presence of a bicuspid valve, severe aortic regurgitation, the occurrence of a stroke within three months and more. Patients were sized with 20,23,26, and 29mm implant and prepared for pre-op. The mean procedure duration was 69.9 29.5 minutes. Technical success defined as absence of procedural mortality and correct positioning of only one valve into the proper anatomical location, was achieved in 99 patients (98%). The mortality rate was a factor being critically considered and all the procedures were completed with zero mortality. The objective of this study was to look at the thirty-day outcomes of all the patients.
Table 1. Thirty-day outcomes. (5) These outcomes are from participants from the study and recorded with the thirty-day follow-up appointment.
The above table shows the thirty-day outcomes of the participants. This was some of the most important data of the study because thirty-day outcomes were the objective. These outcomes are as follows: one patient had died from periprocedural stroke, three patients suffered from strokes all of which were ischaemic and two classified as being disabling, a PPM was implanted in four, twenty had new onset left bundle branch block, seven had new on set atrial fibrillation, two patients suffered from life threatening acute kidney injury, and forty seven of the participants were alive and did not experience adverse events from the implant. There was confirmation of a significant increase in aortic valve effective orifice area and no severe paravalvular leaks or aortic regurgitation.
This study concluded many important factors that support how effective the implantation was.. Having a 1% mortality rate represents the lowest ever reported and suggests that the improved SAPIEN 3 may explain the low rate. This study mimics results that were concluded from high-risk patients, which supports the idea of conducting this procedure on lower risk patients. This study showed only 4.3% rate of implanted PPM in patients, and previous studies done with SAPIEN XT had a much higher rate. The overall conclusion of this study was TAVR using the SAPIEN 3 in intermediate risk patients was conducted as a minimally invasive procedure and had a very high rate of technical success and a very low rate of mortality and complications. Like all scientific studies, there were limitations. This was a non-randomized study with a small sample size. There was also an extensive exclusion rate, so the results conducted cannot be compared or used for the general population. (5)
In conclusion, transcatheter aortic heart valve replacement has been performed worldwide and on thousands of patients. As medical technology advances, implants such as the Edwards SAPIEN 3 transcatheter heart valve have saved patient lives and improved quality of life. This procedure has limited complications and patient mortality when compared to traditional open-heart surgery. It is concluded that TAVR benefits patients who are at high risk for surgery and based on results from studies such as the one listed above, this procedure can one day benefit patients with intermediate and low risk for mortality. TAVR using transfemoral or transapical approaches could one day be the leading option for valve replacements.
With conditions like stenosis and regurgitation, it is important to have advanced technology that mimics the actions of a normal valve. Edwards Lifesciences(6) being the leader of new innovations and technologies has made this possible by constructing implants that are identical in all ways possible to a normal valve. When the FDA approved SAPIEN for commercial use in the United States in 2011, it was already in use in 41 countries worldwide. Because of the bovine tissue used for the leaflets, the Edwards SAPIEN valve is considered a tissue valve. A competing technology is a mechanical valve, which is made from pyrolytic carbon instead. Mechanical valves are mostly bileaflet, and requires patients to be on lifelong blood thinner therapy. The choice between a tissue or mechanical valve is a decision made from many of factors. Some studies show that the mechanical valve is more effective on patients fifty to sixty nine years old. The main drawback if mechanical is a life long commitment to blood thinners.(13) Medicine is constantly changing and new cutting-edge procedures are developing every day. TAVR has increased with advances and can only get better. I predict this procedure using these less invasive approach will replace open-heart surgeries and will be the standard procedure for valve conditions.