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Aortic Valve Sparing
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[62] De Paulis R, Scaffa R, Weltert L, Salica A. Mimicking mother nature: The Valsalva
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In: Perspectives in Aortic Valve Disease ISBN: 978-1-53618-769-4
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Editor: Giovanni Concistrè © 2020 Nova Science Publishers, Inc.
Chapter 21
TRANSCATHETER THERAPY:
DEVICES AND TECHNIQUES
Francesco Maisano
1
University Heart Center, University Hospital, Zurich, Switzerland
2
Fondazione Policlinico Universitario A. Gemelli, IRCSS, Roma, Italia
3
Università Cattolica del Sacro Cuore, Roma, Italia
1,*
and Giulio Russo
ABSTRACT
Transcatheter aortic valve implantation (TAVI) has established as the first treatment
option for symptomatic severe aortic stenosis in inoperable patients and in those at high
or intermediate surgical risk. Last August 2019, the Food and Drug Administration
approved the use of TAVI for the treatment of symptomatic severe aortic stenosis also in
patients at low surgical risk. This approval paved the way to application of TAVR in
patients at all levels of surgical risk. Moreover, some trials are underway to further
investigate possible future indications for TAVI (e.g., asymptomatic severe aortic
stenosis). In spite of this, some technical issues (e.g., durability, pacemaker implantation
rate, antiplatelet regimen…) as well as clinical indications (e.g., asymptomatic severe
aortic stenosis, younger patients, aortic regurgitation…) still remain open and unsolved
and more data are needed to better understand how far the TAVI can go. In this
perspective, TAVI as compared to surgery has gained a central role although it has still
many challenges to overcome.
In this chapter, a detailed overview of main available TAVI prostheses and
techniques are provided with a special focus on some challenging situations.
Keywords: aortic valve stenosis, aortic valve replacement, transcatheter aortic valve
implantation
1,2,3
*
Corresponding Author Email: francesco.maisano@usz.ch.
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INTRODUCTION
TAVI was initially intended for the high or prohibitive surgical risk patient. Although no
clear definition of “high” or “prohibitive/inoperable” risk existed, a risk of 15-50% or >50%
of surgical mortality or permanent disability, respectively, were arbitrarily defined to select
patients unsuitable for cardiac surgery and for which the percutaneous approach was the only
feasible one (Table 1). This led to a renewed interest in cardiac surgical risk algorithms and
put the “Heart Team” in a central role in the patient assessment. At the same time several
operative risk scores were developed [1-4] although the two most used are the European
System for Cardiac Operative Risk Evaluation (EuroSCORE) and that of the Society of
Thoracic Surgeons (STS). The EuroSCORE II has been found to be a better predictor of
mortality than the original logistic EuroSCORE but nonetheless still lacks discriminatory
power and is outperformed in TAVI patients by the STS-PROM score [5]. A EuroSCORE II
of >10% or an STS >8 are considered to indicate high risk with respect to TAVI, while an
STS score <4 defines low risk patients. Despite their known limitations, the enrolment of
“high surgical risk” patients into TAVI trials, [6, 7] was based upon the logistic EuroSCORE
I and the STS operative risk scores.
Table 1. Risk classification in cardiac sugery patients
Current European guidelines recommend TAVI in patients who are not suitable for
surgical aortic valve replacement (SAVR) as assessed by heart team [8]. Some clinical (e.g.,
age >75, frailty, prior cardiac surgery…) and anatomical (porcelain aorta, expected patientprosthesis mismatch, valve and aortic root morphology…) features may help to choose
between the two approaches although no clear indications are proposed and choice is mainly
based upon local heart team assessment and experience.
Last August 2019, the U.S. Food and Drug Administration (FDA) approved the TAVI
use for the treatment of symptomatic severe aortic stenosis in patients at low surgical risk
formalizing the application of TAVR in patients at all levels of surgical risk. FDA decision
was based upon the results from the PARTNER 3 and Evolut Low Risk clinical trials (Figure
1).
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Figure 1. FDA decision based upon results from PARTNER 3 and Evolut Low Risk clinical rials.
The PARTNER 3 trial was randomized clinical trial comparing TAVI with the Edwards
Sapien 3 system and SAVR in symptomatic aortic stenosis patients with STS score <4% [9].
The primary endpoint (a composite of all-cause death, stroke, or rehospitalization) at 1 year
was lower in the TAVI group as compared to the SAVR group (8.5% vs. 15.1%; P = 0.001
for superiority). These data demonstrated the superiority of Sapien 3 balloon expandable
prosthesis over surgery supporting the use of TAVI also in low risk category. Similar results
came from the Evolut Low Risk clinical trial, which compared the Medtronic Corevalve selfexpandable technology (Corevalve, Evolut R and Evolut Pro) to SAVR in low risk patients
(STS score <3) [10]. Such data pave the way for a larger TAVI use, although long term data
are still lacking and several issues remain still open.
TAVI DEVICES
Valves Prostheses
Currently there are several percutaneous prosthetic aortic valve systems with CE mark
approval and they are classified according to their deployment mechanism (Figure 2):
Balloon-expandable: the SAPIEN family valves (Edwards Lifesciences, Irvine, CA,
USA) are those with widest experience and available data. More recently, the Meril
Myval (Meril Lifesciences, Pvt. Ltd., India) has gained the CE mark.
Self-expandable: the most studied and most implanted model is represented by the
Corevalve family valves (Medtronic Inc, MN, USA). However, several devices
belong to this category and each has its own peculiar features.
Mechanically-expandable: the LOTUS (Boston Scientific Corporation, MA, USA) is
the only example for this group.
The latest generation devices addressed some of first-generation devices issues such as
paravalvular leak (PVL) regurgitation, mispositioning, atrio-ventricular block and the
potential for vascular access complications. In this perspective the newest devices have
different design and smaller diameter sheath and more precise device deployment
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mechanisms. However, still some open issues remain in this field and pacemaker
implantation, prostheses durability, coronary obstruction risk and best antiplatelet/
anticoagulant will some of the future challenge for transcatheter aortic valve implantation
(TAVI) devices.
Figure 2. TAVI portfolio.
Sapien (Edwards Lifesciences, Irvine, CA, USA)
The very first model was pioneered by Cribier-Edwards in 2002. Currently, three models
are available: SAPIEN XT, SAPIEN 3 and the brand-new SAPIEN 3 Ultra (Table 1).
They use the bovine pericardial tissue as for the Edwards surgical valves, and have
dedicated outer skirt to reduce PVL risk and a row of large cells struts to allow easier
coronary access. As compared to most of the self-expandable models, the SAPIEN family has
the lowest profile. They can be implanted through either the transfemoral or the transapical
route. In order to use smaller sheaths introducers, the balloon and the prostheses are
assembled in the descending aorta for the XT and 3 models, whereas the newest Ultra valve is
crimped on the balloon and has a lower crossing profile. During deployment SAPIEN XT
frame foreshortens homogenously while the SAPIEN 3 has more foreshortening in the lower
two-thirds compared to the upper one-third of the frame. Moreover the SAPIEN 3 needs to
less oversizing than the XT in most cases unless the size falls in between two different size
according to company size chart, in which case oversizing by 10-20% may be advisable.
Medtronic CoreValve (Medtronic Inc, MN, USA)
The CoreValve system is the most studied self-expandable model and following its first
platform, three new system have been launched: the EVOLUT R, EVOLUT PRO and
EVOLUT PRO+. It is a self-expanding valve made of single layer porcine pericardium in a
trileaflet configuration with a scalloped skirt in a nitinol frame. The EVOLUT PRO models
have an external pericardial wrap to improve the annulus sealing and to reduce the PVL risk.
Of note, its supra-annular position allows it to maintain a circular configuration at the level of
the valve leaflets achieving larger effective orifice area and optimizing coaptation in non
circular anatomy.
Unlike the SAPIEN models, the EnVeo Pro delivery system does not require any sheath
introducer allowing lower access site dimensions. Once mounted, the needs to be checked
fluoroscopically in the anteroposterior projection and rotated to ensure that the paddles and
their attachments are equidistant. Due to its supra-annular design, hemodynamic instability
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may occure during its deployment. The valve is resheatable, repositionable and retrievable
and has been mainly used for transfemoral approaches although it is suitable for all
approaches but the transapical.
Portico (St. Jude Medical, CA, USA)
It is a self-expanding nitinol valve platform with bovine pericardium valve at annular
level. The stent large cells facilitate its accommodation in calcific native valve and coronary
reaccess. Due to lower radial force, the aortic valve pre-dilation is highly recommended. Its
new Flexnav transfemoral delivery system increases flexibility and trackability decreasing the
risk for vascular complications. Alongside this, a different delivery system allows also the
transapical approach. Similarly to CoreValve system, it is re-sheathable, re-positionable, and
retrievable until 80% of the device is deployed in the aortic annulus. The valve can then be
assessed for stability and function prior to final release.
Acurate Neo (Boston Scientific Corporation, MA, USA)
This self-expanding valve platform is the transfemoral version of the transapical device.
It is made of porcine leaflets with upper and lower crowns and stabilization arches. Like the
CoreValve it has a supra-annular design. A distinguishing feature is the top-down deployment
to increase hemodynamic stability and precise implantation. Consequently, during the
deployment sequence, the upper crown expands first, followed by the arches and finally the
lower crown: the upper crowns are responsible for supra-annular anchoring of the prosthesis
and capping of the native leaflets, stabilization arches contribute to axial self-alignment, and
the pericardial skirt acts as a seal to prevent PVL.
Lotus (Boston Scientific Corporation, MA, USA)
It consists of three bovine pericardial leaflets attached to a braided nitinol frame with a
radiopaque marker used for accurate placement. The valve is designed to expand radially as
the valve shortens during deployment. Rapid pacing is not required during the implantation
and it is fully repositionable during deployment and retrievable prior to release. This together
with very controlled deployment mechanism and an adaptive seal limits PVL and
malpositioning. The valve functions early in deployment, providing hemodynamic stability
for the patient.
Allegra (New Valve Technology, Switzerland)
It is a self-expanding device made of a nitinol stent frame and a bovine pericardium
(annular skirt and leaflets). The delivery system has a 18 Fr cartridge and 15 Fr catheter shaft.
Valve deployment is in three steps: first, the central part of the valve is released, while both
ends of the device are still captured. During the second step, the bottom of the valve is
released allowing the operator to assess valve position, patency of the coronaries,
hemodynamic functions, and paravalvular regurgitation. The process can be re-started till this
step, and the valve can thus be retrieved. In the final step, after the operator confirms the
position of the prosthesis, the safety locker is released for final deployment of the Allegra
valve.
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Myval (Meril Lifesciences, Pvt. Ltd., India)
The latest technology to get the CE mark approval is Myval. It is a balloon-expandable
valve, made of bovine pericardium tissue in a nitinol-cobalt alloy frame. Similarly to other
prostheses technology, the lower closed cell part of the valve frame is covered externally with
a protective sealing cuff in order to reduce PVL. The crimped valve is inserted through a 22Fr
or 24Fr (based on prostheses size) expandable sheath.
TECHNIQUES
Transfemoral Approach
Access Site Management
Transfemoral artery is the most used approach accounting for more 90-95% of all TAVI
used accesses. Often it is performed under local anesthesia with or without sedation, while
deep/general anesthesia and intubation is reserved for non-femoral approaches or complex
femoral procedures.
Currently half of all transcatheter procedures are performed under general anesthesia
worldwide. Alongside the arterial access for TAVI, a second arterial access is needed in order
to have continuous invasive pressure monitoring, to perform angiography and, in case
vascular complication, for bail-out procedures. Currently, several vascular accesses sites
settings have been proposed (figure 3).
Figure 3. Vascular accesses sites for TAVI procedure.
The contralateral femoral artery and the radial artery are the most common used ones.
Recently, a less invasive technique (LITE) based on the use of radial artery as ancillary access
and retrograde guidewire pacing has been described by Burzotta et al. [11]. Moreover, data
coming from a multicenter study accounting almost 5000 patients undergoing TAVI
demonstrated a lower rate of vascular and bleeding complications in those using radial artery
as secondary access as compared to femoral [12].
Due to the use of large bore sheaths, femoral puncture should always be guided by
ultrasound, fluoro or both (Figure 4).
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Figure 4. Echo-guided femoral puncture.
Once the artery access has been gained, preclosure devices such as Proglide (Abbott
Vascular, Redwood City, CA) or Prostar (Abbott Vascular Inc, Santa Clara, CA) are
implanted.
Although these percutaneous devices originally were not designed for TAVI, now they
have CE approval and are able to close arteriotomies up to 24Fr in diameter.
Vascular outcomes with the use of preclosure devices as compared to surgical repair have
been investigated showing a slight advantage for percutaneous devices provided that
operators gain experience and know how to manage possible vascular or bleeding
complications, [13, 14]. Manual compression as well as the use of additional devices such as
Femostop II or Angioseal together with protamine administration are often used to achieve
hemostasis.
Temporary Pacemaker Implantation
Temporary pacing is required for pre-dilation, post-dilation, or prosthesis deployment
under rapid pacing to prevent device ejection by systolic contraction. In addition, it serves as
protection against the potential development of bradyarrhythmia following TAVI. The right
internal jugular vein or femoral vein is used typically. Alternatively, the use of guidewire for
pacing in order to reduce vascular access sites and related complications has also been
described [11, 15]. However, in those with higher risk for bradyarrhythmia (e.g., pre-existing
atrio-ventricular block, right bundle branch block…) temporary venous pacing is advisable.
During the procedure, pacing rates must be high enough to cause a fall in systolic BP and this
typically occurs >160-220bpm. At the end of the procedure, temporary pacing might be
removed in case of no ECG changes, especially if a balloon-expandable valve has been
implanted. On the contrary, if some ECG changes occur (P-R segment prolonging, any
atrioventricular or bundle branch block) temporary pacing should left in place and ECG
assessed in the following hours/days.
Valve Implantation
After vascular and temporary pacing management, aortic valve crossing is the next step
for the prostheses implantation. A standard straight-tipped wire through an Amplatz catheter
in the LAO projection is commonly used to cross the native valve. Alternative catheters such
as an internal mammary or Judkins right can be used (horizontal aorta) and hydrophilic wires
can also be used in particularly challenging cases.
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A pigtail catheter is placed in the non-coronary sinus of Valsalva and aortic root
angiography is used to determine the position of equipment relative to the coronary cusps.
Balloon valvuloplasty prior to prostheses implantation serves the purpose to prepare the
aortic landing zone for TAVI, especially in severely calcific aortic valves. Importantly, the
size of the balloon should not exceed the minimum aortic annulus diameter as measured from
the CT scan. Massive aortic regurgitation may follow balloon pre-dilatation, consequently,
TAVI device should be ready for implantation before valvuloplasty. Although some devices
strongly suggest pre-dilatation, it is not required for all of them and the operator experience
plays a key role to assess clinical and anatomical characteristics to identify those cases in
which valvuloplasty should be performed or not.
Following this, device positioning should be assessed carefully. In order to do so, the
aortic annular plane (the nadirs of the non, right and left coronary cusp leaflets) should be
perpendicular to the valve device and co-axially aligned. Modern computed tomography
analysis softwares allow to calculate the “three cusps view” and the correct annular
alignment, which can also be found with the “following the right cusp” rule [16]. More
recently, the “cusp overlap” view has been proposed by Tang et al, in order to reduce the rate
of permanent pacemaker implantation rate [17]. Correct implantation depth is a critical
feature of a successful implant. Accurate placement of the prosthesis requires visualization of
both the aortic annulus plane and that of the device delivery catheter overlap perpendicularly.
Before final deployment, self-expandable devices allow to recapture and re-implant the
device in order to obtain the correct position. Too deep implantation has been associated to
higher PVL risk and higher permanent pacemaker implantation. In some cases, post dilatation
can be required in order to reduce PVL and better expand the prostheses against the annulus.
ALTERNATIVE APPROACHES
Subclavian/Transaxillary
This the most frequent non-femoral access point used, according to the TVT registry data
[18]. Higher incidence of stroke was observed in comparison to transfemoral route although
reported vascular complications were not significantly higher.
It is more frequently performed via a surgical cut-down when in the subclavian portion. If
transaxillary it can also be performed percutaneously with pre-closure sutures most frequently
into the proximal third of the axillary artery. A left-sided approach is selected in >95% of
cases due to a more favorable alignment of the prosthesis with the native valve, while the
angulation at the subclavian-aortic junction may vary according to the aortic arch anatomy.
The presence of a LIMA graft should always be considered and may represent a relative
contra-indication. Of note, dissection and/or bleeding can be challenging to control even with
open surgical access. For this reason, it is advisable to choose and to learn only one
alternative access site on order to master it and the related complication.
Transaortic
A right anterior mini-thoracotomy is used for patients with a right sided ascending aorta
or patent coronary bypass grafts and a mini-J sternotomy for middle or left-sided ascending
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