In this article, we will discuss Transcatheter Aortic Valve Replacement (Methods of Implantation). So, let’s get started.
Methods of Implantation
The valve implants are done with either retrograde or antegrade approach and the selection of the approach is based on the patient’s vascular anatomy and diameters.
For the retrograde approach, most of the procedures are performed via percutaneous transfemoral (TF) approach. In the absence of femoral access, transaortic (TAo) or transsubclavian (TS) accesses are more common. Transcarotid and transcaval accesses can be considered but are significantly less common at the current time. Most of the TF procedures are performed under monitored anesthesia care or conscious sedation. All other types of retrograde and antegrade implant procedures are mini-surgical procedures and require general anesthesia. They are usually performed with transesophageal echocardiogram guidance.
All TAVR procedures (retrograde and antegrade) require a temporary pacemaker for rapid burst pacing (for Edwards Lifesciences) or rhythm override (for Medtronic, Dublin, Republic of Ireland). A pigtail catheter is also needed for aortic root injections to guide valve implantation. For Edwards Lifesciences, it is placed in the right cusp and for Medtronic it is placed in the noncoronary cusp. The pigtail catheter is inserted thru femoral, radial, or brachial arterial access. The temporary pacemaker is usually inserted via femoral or internal jugular venous access.
A core team is identified for the valve implant procedure. At our institution, this team includes a cardiovascular surgeon (first operator), an interventional cardiologist (second operator), hemodynamic technician (to operate the pacemaker), and an anesthesiologist. If a second interventional cardiologist is available, he or she acts as an assistant. For implantation of the Edwards Lifesciences THV, the first operator is responsible for the finer adjustment of the delivery system. The second operator is in-charge of initiating the implant sequence and is responsible for aortography and inflating balloon to deploy the valve. For implantation of the Medtronic THV, the responsibilities remain the same; however, the second operator is also responsible to unsheath the valve. The valve team is constantly in sync with each other throughout the procedure. It is essential to check the orientation of the valve before inserting into the sheath. It is also important to standardize the valve implantation sequence with the team and practice it multiple times before the real procedure.
Anticoagulation is maintained with a target activated clotting time of 300 ± 25 seconds. Rapid burst pacing is kept to the minimum for patients with compromised left ventricular (LV) function. At our institution, we try to maintain systolic blood pressure of approximately 110 to 120 mm of Hg before the valve implantation sequence.
For TAO and transapical (TA) accesses, a shorter delivery system is used thru a larger 24F catheter sheath. Apart from the access site management, the valve deployment sequences remain the same. The only change in TA access is the orientation of the mounted valve, which is exactly opposite to the valve mounted for the retrograde access.
Evolution of Transcatheter Aortic Valve
Currently there are only two companies that offer commercially available THVs:
Edwards Lifesciences and Medtronic.
Edwards Lifesciences was the first company to market with a commercial THV, in November 2011, the Sapien THV. The Edwards Sapien THV was comprised of a balloon-expandable, stainless steel frame, three bovine pericardial tissue leaflets and a polyethylene terephthalate (PET) fabric skirt. The PET fabric skirt was sewn on the inner portion of the bottom of the stent frame to help seal the aortic annulus and reduce the amount of paravalvular leak (PVL). The leaflets were treated according to the Carpentier-Edwards ThermaFix process, which is intended to reduce the buildup of calcium overtime. The Sapien THV is currently no longer available for implantation but was available in two sizes, 23 mm and 26 mm. The 23-mm valve was delivered through a 22F catheter sheath if placed using TF access or a 26F catheter sheath if delivered using TA access. The 26-mm valve was delivered through a 24F catheter sheath if placed using TF access or 26F catheter is placed using TA access. In March of 2010 Sapien XT, Edwards Lifesciences second-generation THV, received CE mark for approval. The Sapien XT THV also consists of a balloon-expandable frame; however, the frame is constructed using cobalt-chromium instead of stainless steel. Three bovine pericardial leaflets treated with the Carpentier-Edwards ThermaFix process and an inner PET fabric skirt were also used. The improvements seen in the Sapien XT THV allows for expanded annular size coverage, smaller sheath sizes, and expanded access routes to include TAO. Four sizes of Sapien XT THV are available: 20 mm, 23 mm, 26 mm, and 29 mm. When delivered using TF access, a sheath size of either 16F. 18F, or 20F catheter is used. When delivered using Tao or TA access, a 24F catheter sheath for the 23-mm or 26-mm valve is used and a 26F catheter sheath for the 29-mm valve is used.
In June 2015, Edwards Lifesciences received FDA approval for their third-generation THV: Sapien 3. This valve also consists of a balloon-expandable cobalt chromium frame; however, the frame’s geometry was altered to allow for lower delivery height and reduction in delivery profile. There are still three bovine pericardial leaflets, which are also treated with the Carpentier-Edwards ThermaFix process. A PET fabric outer skirt was added in addition to the PET fabric inner skirt to further seal the aortic annulus and further reduce the amount of PVL The Sapien 3 THV has been approved for TF, TA, TAO, or TS. When delivered using TF. TAo, or TS access, a 14F catheter sheath is used for the placement of a 23-mm or 26-mm valve and a 16F catheter sheath is used for the placement of a 29-mm valve. When delivered using TA access, an 18F catheter sheath is used for the 23-mm or 26-mm valve and a 21F catheter sheath for the 29-mm valve.
In January of 2014, Medtronic announced FDA approval of its CoreValve THV, making
it the second commercially available system on the market. The second-generation Medtronic THV, CoreValve Evolut R, was approved by the FDA in June of 2015. Both the CoreValve and CoreValve Evolut R THV systems are comprised of three porcine leaflets and an inner porcine skirt sutured to a self-expanding nitinol frame. Both the CoreValve and CoreValve Evolut R have three distinct segments: the base portion which exerts a high radial force that expands and pushes aside the calcified leaflets (of the native valve); the central portion which carries the valve; and the top portion which flares to fixate and stabilize the valve in the ascending aorta”. The Evolut R features an improved design to the nitinol frame with a lower delivery height, reduced delivery profile, and expanded sealing skirt to further reduce the amount of PVL The other significant improvement in the CoreValve Evolut R is the ability to recapture the THV once partially deployed allowing for repositioning within the annulus. The CoreValve THV is available in three sizes: 26 mm, 29 mm, and 31 mm fitting annular dimensions ranging from 20 mm to 30 mm using an 18F catheter sheath. The CoreValve Evolut R THV is available in four sizes: 23 mm, 26 mm, 29 mm, and 34 mm fitting annular dimension ranging from 18 mm to 30 mm using a 14F catheter sheath for the 23 mm, 26 mm, or 29 mm and a 16F catheter sheath for the 34 mm. Both the CoreValve and CoreValve Evolut R THV are delivered using TF, TAO, or TS access.
Current Indications for Transcatheter Aortic Valve Replacement
TAVR using all commercially available THV has an indication for use in patients with symptomatic heart disease caused by severe, calcific native, or prosthetic AS who meet an indication for SAVR but are considered to have at least intermediate surgical risk for implantation of the Edwards Lifesciences S3 or Sapien XT THVs or high to prohibitive surgical risk for the Medtronic CoreValve and CoreValve Evolut R THVs.