Self-expanding transcatheter aortic valve replacement: The medtronic corevalve system
Currently in the United States, the most widely used self-expanding transcatheter aortic valve is the Medtronic CoreValve system. This transcatheter valve is made of a self-expanding nitinol frame with leaflets composed of porcine pericardium. The Medtronic CoreValve system has undergone two design iterations to improve the outcomes after implantation based on trial and registry data. The first-generation Medtronic CoreValve was evaluated in the CoreValve US Pivotal Trial, which had two main studies: the extreme-risk and the high-risk study. The CoreValve US Pivotal Trial Extreme Risk Study looked at the outcomes of transcatheter aortic valve replacement (TAVR) in patients with severe aortic stenosis who have a prohibitive risk for surgery. The endpoint of all-cause mortality and major stroke in the TAVR arm was noninferior to that in the medical therapy arm. The second CoreValve US Pivotal Trial High Risk Study was a prospective randomized study comparing outcomes of patients with severe aortic stenosis and high surgical risk undergoing surgical aortic valve replacement (SAVR) to TAVR. At 1-year follow-up, TAVR was shown to be noninferior to SAVR with respect to mortality and stroke endpoints. There was less major bleeding and atrial fibrillation with TAVR compared with SAVR; however, there were more vascular complications and greater need for a pacemaker and larger paravalvular leak in the TAVR arm. These trials led to Food and Drug Administration (FDA) approval of the Medtronic CoreValve system in patients with high or prohibitive surgical risk. To improve the outcomes pertaining to bleeding, paravalvular leak, and pacemaker need, several changes were made to the device design itself ( Fig. 9.1 ). The second-generation Medtronic CoreValve Evolut R had a lower height to improve the hemodynamics and an extension distally to the skirt for a better seal to improve the paravalvular leak rate. The delivery system also improved with an in-line sheath that brought the diameter of the delivery system from 24F to 14F to lessen the vascular complications ( Fig. 9.2 ). It also provided a recapture feature, which allowed better positioning to prevent deep implantation, which can cause a heart block needing pacemaker implantation.
The next clinical trial looked at outcomes of TAVR versus SAVR in intermediate-risk patients with severe aortic stenosis. Sixteen percent of the CoreValve devices used in this trial were the second-generation Evolut system. The trial showed that TAVR was noninferior to SAVR with respect to the combined endpoint of mortality and stroke, with higher rates of paravalvular leak and pacemaker insertion in the TAVR arm. These results led to the approval of the use of a self-expanding valve in patients with severe aortic stenosis and intermediate surgical risk. In a subgroup analysis of this trial, the second-generation device design did not seem to have affected the outcomes related to pacemaker and paravalvular leak, although it only was used in a small number of patients. Registry data studies, however, showed that the use of the CoreValve Evolut R was associated with lower rates of moderate to severe paravalvular leak, vascular complications, and pacemaker implantation. The device underwent further design changes, which led to the most recent iteration called the Medtronic CoreValve Evolut Pro, which had an additional external pericardial layer around the skirt to provide a better seal and lower the risk of paravalvular leak. Outcomes of CoreValve Evolut Pro are still being studied. One important caveat is that the newer Evolut Pro does not come in a 34-mm size and requires the use of a 16F in-line sheath as opposed to the 14F in-line sheath in most of the models of the second-generation CoreValve Evolut. Therefore the CoreValve Evolut Pro device requires a cutoff of a 5.5-cm vessel diameter to allow passage of the delivery system.
Patient selection
Candidates for TAVR include patients with severe aortic stenosis at an intermediate, high, or prohibitive risk for SAVR, as well as for a failed surgical aortic bioprosthesis who have a high risk for open surgery. Optimal candidates should have an acceptable 1-year survival to be considered for TAVR.
Patients with known hypersensitivity to any medication or component used during the procedure, active sepsis or endocarditis, and mechanical valves have a contraindication for this procedure. Anticoagulation should be held for this procedure, with low-molecular-weight heparin bridging used for those at risk for thromboembolic events.
The following are patient anatomic factors that are important when considering the use of the self-expanding CoreValve system:
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Severe annular calcification: use of a self-expanding system rather than a balloon-expandable system is preferable in these patients to help prevent annular rupture
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Failed surgical bioprosthetic valves with a small diameter: given the CoreValve’s supraannular position, the effective orifice area (EOA) is larger with the CoreValve compared with the equivalent balloon-expandable annular TAVR prosthesis.
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Patients at high risk of coronary obstruction: due to the advantage of a recapturable system, although if coronary obstruction occurs after deployment of the valve, cannulation of the coronary ostium can be more challenging with the CoreValve system compared with the balloon-expandable valve.
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Patients with poor cardiac reserve who cannot tolerate rapid pacing because the CoreValve can be deployed without requiring rapid pacing, especially when the cardiac function is diminished.
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Horizontal aortas do not favor the use of a self-expanding valve, and the flexible delivery system with the balloon-expandable device offers better alignment with the valve orientation.
Procedural planning
Every patient who is being evaluated for this procedure has to be seen by a noninterventional valve specialist, cardiovascular surgeon, and interventional cardiologist, and a decision has to be made by the entire heart team. For procedural planning, patients would typically need the following testing:
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Transthoracic echocardiography
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Cardiac computed tomography angiogram (CTA) and CTA of the chest, abdomen, and pelvis
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Coronary angiogram
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Labs
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Electrocardiogram (ECG)
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Chest x-ray
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Pulmonary function testing
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Frailty evaluation
The following steps in planning are for native aortic valve stenosis. The next section will discuss specific considerations in planning valve-in-valve procedures.
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Access planning: Transfemoral access is used for 90% of procedures and is the main focus of this chapter ( Fig. 9.3 ). Alternative access can be used when femoral access is not available; this is described in Chapter 11 .
CTA of the abdomen and pelvis is used to evaluate candidacy for transfemoral access. Measurements are performed along the diameter of the common femoral, external iliac, common iliac, and abdominal aorta on a double-oblique axis using reformatted images and by measuring the minimal luminal diameters, excluding the calcified portions. Adequate vessel diameter should be more than or equal to 5.5 mm for the Evolut Pro and the 34-mm Evolut R, whereas it should be more than or equal to 5 mm for the 23-, 26-, and 29-mm Evolut R CoreValve. Next, evaluation of anterior calcification is performed by looking at the axial cross-sectional images at the level of the femoral head, paying particular attention to the presence of anterior calcification. The presence of anterior calcium in the common femoral artery at the level of the femoral head precludes use of a Perclose device and increases the risk of vascular complications and would be an indication to proceed with alternative access. Following that, attention is paid to the tortuosity across the path of the valve from the common femoral artery all the way to the aortic root. Many times, the tortuosity straightens when a stiff wire is used during the procedure, and this can be evaluated during the preprocedural coronary angiogram by placing a stiff wire and seeing if that straightens the tortuosity. Also, the presence of any plaque, calcification, dissection, or aneurysm along the pathway of the delivery system or catheters should be noted and factored in the decision-making. Finally, in cases where an embolic protection device is anticipated, the origin of the right brachiocephalic artery and the left common carotid artery should be assessed to make sure no significant plaque is present.
Fig. 9.3
Access planning for transfemoral transcatheter aortic valve replacement (TAVR).
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Aortic root: The next step in planning is to focus on the aortic root ( Fig. 9.4 ).
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Sizing: Sizing of the self-expanding valve is made by measuring the annular perimeter (not area). After a size is chosen, the next step is to ensure that the other measurements, including the sinus of Valsalva diameter and height, are adequate to accommodate the shape of the valve chosen.
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Orientation of the root: The CTA provides the coplanar angle, which is the fluoroscopic angle at which the noncoronary right and left cusp are aligned and is important for valve positioning and deployment. As mentioned, horizontal aortic roots are less favorable for self-expanding valves because the delivery sheath can bias one side of the aortic wall, which would make it difficult to position and deploy the valve coaxially.
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Calcification: The presence of heavy calcification in the leaflets and/or left ventricular outflow tract is a risk factor for paravalvular leak, annular rupture, and heart block. This favors self-expanding valves over balloon-expanding valves, given the risk of annular rupture, although care should be taken if predilation or postdilation of the valve is required when using a self-expanding valve.
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Coronary arteries: A coronary angiogram is performed to assess for the presence of an obstruction or atherosclerosis. Percutaneous coronary intervention is performed if there is a large ischemic territory, such as the proximal left anterior descending artery or left main coronary artery.
The risk of coronary artery obstruction, by displacing a calcified leaflet or by prosthetic leaflet eclipse, is increased when the coronary height, measured from the annulus to the origin of the left or right coronary artery on the cardiac CTA, is less than 10 cm and/or the sinus of Valsalva diameter is less than 28 cm on average.
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Rhythm-related considerations: A baseline ECG is important to assess the risk of needing a pacemaker. A baseline right bundle branch block increases that risk. If the patient has a device with a defibrillator function, the latter should be temporarily deactivated during the TAVR procedure. One of the advantages of self-expanding valves is that it is possible to deploy these valves without needing rapid pacing, which is important in patients who have poor cardiac function and depressed ejection fraction.
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