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Available online at www.sciencedirect.com

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Balloon-Expandable Prostheses for Transcatheter Aortic Valve Replacement Henrique Barbosa Ribeiro, Marina Urena, Ricardo Allende, Ignacio J. Amat-Santos, Josep Rodés-Cabau⁎ Quebec Heart & Lung Institute, Laval University, Quebec City, Quebec, Canada

A R T I C LE I N F O

AB ST R A C T

Keywords:

The implantation of a transcatheter heart valve (THV) through a balloon-expandable

Aortic stenosis

system played a major role in the early stages of transcatheter aortic valve replacement

Transcatheter aortic

(TAVR). The technology consists of sewing a foldable biological cardiac valve inside a

Valve replacement

metallic stent frame, and then crimping the device into a balloon in order to implant the

Transcatheter heart valve

valve at the level of the aortic annulus through balloon inflation. The use of balloon-

Balloon-expandable

expandable valves underwent a rapid expansion in the years following the pioneering experience of 2002, and recent large multicenter trials and registries have confirmed the safety and efficacy of TAVR using balloon-expandable valves. The randomized Placement of Aortic Transcatheter Valves (PARTNER) trial showed both the superiority and noninferiority of TAVR with the balloon-expandable Edwards-Sapien system compared to medical treatment (non-operable patients) and surgical aortic valve replacement (high risk patients), respectively. Balloon-expandable valves have been associated with excellent hemodynamic results (residual mean gradient < 15 mm Hg in most cases), though residual paravalvular aortic regurgitation is frequent (trivial or mild in the majority of patients, moderate or severe in < 10%). Valve durability studies with up to 5-year follow-up have shown maintained valve hemodynamics over time with only a minimal decrease in valve area and no increase in aortic regurgitation. Future improvements in the balloonexpandable THV technology such as implementing anti-paravalvular leak features (ex. Sapien 3 valve), and showing its efficacy for the treatment of non-high risk patients (ongoing PARTNER II trial) will probably lead to broader use in a lower risk population in the near future. © 2014 Elsevier Inc. All rights reserved.

The concept of a transcatheter heart valve (THV) was first tested in vivo in the early 90’s, in a porcine model followed a decade later by the first percutaneous implantation of a prosthetic valve in a pulmonary conduit.1,2 In 2002, the first implantation of a THV in the aortic position was performed by Cribier et al. for the treatment of severe symptomatic aortic

stenosis (AS) in a patient considered inoperable.3 All of these early experiences were performed with a balloon-expandable THV system, where a prosthetic tissue valve was conceived with a foldable biological cardiac valve sewn inside an expandable stent frame, with the device subsequently crimped into a balloon in order to deploy the THV through balloon

Statement of Conflict of Interest: see page 592. ⁎ Address reprint requests to Dr. Josep Rodés–Cabau, Quebec Heart & Lung Institute, Laval University. 2725, Chemin Ste-Foy, G1V 4G5 Quebec City, QC, Canada. E-mail address: [email protected] (J. Rodés-Cabau). 0033-0620/$ – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.pcad.2014.02.001

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Abbreviations and Acronyms

inflation. The balloonexpandable valve conAR = aortic regurgitation cept therefore played a AS = aortic stenosis major role from the very beginning of the CVE = cerebral vascular events THV experience. PARTNER = Placement of Aortic The expansion of Transcatheter Valves the THV technology was very rapid in the SAVR = surgical aortic valve years following these replacement remarkable pioneering TAVR = transcatheter aortic experiences, and transvalve replacement catheter aortic valve replacement (TAVR) has THV = transcatheter heart valve since become the stanVARC = Valve Academic Redard of care for pasearch Consortium tients with severe symptomatic AS considered to be non-operable, and a well-established alternative for those at high surgical risk. 4 The objectives of this article were to review the main characteristics of the balloon-expandable THV systems used for TAVR, the mechanisms of implantation, and the short- and long-term outcomes, valve hemodynamics and durability associated with such systems.

Prosthetic valve system The clinical experience with balloon-expandable THV commenced with the Cribier-Edwards balloon-expandable aortic stent valve (Edwards Lifesciences, Irvine, CA), which consisted of a trileaflet tissue valve of equine pericardium

mounted in a stainless steel frame.3,5 This was the first THV prototype implanted in humans and subsequent improvements in the valve and delivery systems resulted in the second generation of balloon-expandable THVs, the EdwardsSapien THV (Edwards Lifesciences, Irvine, CA) (Figs 1 and 2).3-5 This valve also consists of a tubular slotted stainless-steel stent frame, but it integrates a unidirectional trileaflet tissue valve made of bovine pericardium, which is pretreated to decrease valve calcification. Moreover, the fabric skirt, made of poly-ethylene terephthalate, extends further to improve sealing and potentially reduce paravalvular regurgitation. This valve is available in two sizes, with expanded external diameters of 23 and 26 mm, requiring 22 F and 24 F delivery catheters for transfemoral approach implantation, respectively (Figs 1 and 2). The Sapien XT valve (Edwards Lifesciences, Irvine, CA) is the 3rd generation of balloon-expandable Edwards valves, which also consists of a trileaflet pericardial bovine valve, but unlike those of the previous generation, it is mounted in a cobalt chromium stent frame (Fig 1). The stent frame design of the Sapien XT valve has fewer rows, columns and vertical struts between commissure pots, which in addition to the scallop shape design of the leaflets, contributes to decreasing the profile of the valve. Also, the leaflets are in a partially closed configuration even when opened, which may reduce the likelihood of interaction between native and prosthetic leaflets. 6,7 The Sapien XT valve is available in 20-, 23-, 26- and 29-mm sizes, and is implanted through the transfemoral approach using the NovaFlex delivery system implanted through 16 F (20-, 23-mm valves), 18 F (26-mm valve) or 20 F (29-mm valve) expandable sheaths (e-sheath, Edwards Lifesciences, Irvine, CA) (Figs 1 and 2).

Fig 1 – Photographs of the balloon-expandable Sapien valves and their respective characteristics. (A) Edwards-Sapien, (B) Sapien XT, and (C) and Sapien 3 valves.

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Fig 2 – Photographs of the transfemoral delivery systems with their respective characteristics for the (A) Edwards-Sapien, (B) Sapien XT, and (C) and Sapien 3 valves. The newer generation delivery catheter for the Sapien 3 valve (Commander) exhibits a much higher flexibility which may improve the coaxial alignment of the transcatheter heart valve system within the aortic annulus. Abbreviations: ID, internal diameter; OD, outer diameter.

The Sapien 3 THV (Edwards Lifesciences, Irvine, CA) is the latest generation of the balloon-expandable valves, and it also consists of a trileaflet pericardial bovine valve that is mounted in a cobalt chromium stent, which also incorporates an additional outer skirt to further fill paravalvular gaps and reduce paravalvular leak (Fig 1). 8,9 Also, the crimped frame is 27 mm high, shortening to 20 mm when deployed. This expanded length is slightly longer than the currently available Sapien (16.1 mm) and Sapien XT (17.2 mm) THVs, and these improvements may facilitate optimal positioning within the native aortic valve and annulus (Figs 1–3). Finally, the delivery system (Commander) has an even lower profile and incorporates some improvements (ex. increased flex properties) to facilitate valve alignment and proper position (Fig 2). 8,9

Implantation: approaches and technique The first TAVR with the balloon-expandable valve was performed antegradely through the femoral vein, followed by a transseptal puncture, crossing the mitral valve and finally positioning and implanting the THV in the aortic annulus.3,5 This initial approach was complex and difficult to reproduce, and improvements in the prosthesis and delivery system caused it to be rapidly supplanted by the transfemoral and transapical approaches.10–12

Transfemoral approach The transfemoral approach has become the first access choice in the vast majority of the centers. Following an accurate evaluation of the iliofemoral anatomy using computed tomography the procedure might be performed under general anesthesia or profound sedation, either in a catheterization laboratory or in a surgical hybrid room. Femoral artery access for the procedure was initially obtained with surgical cutdown; nonetheless, most centers are currently using a fully percutaneous approach. 13,14 Recommended femoral diameters for the different Sapien valves are shown in Fig 2.

Transapical approach The transapical TAVR technique was first reported in 2006, and it was developed for patients with non-optimal iliofemoral vessels that precluded the safe placement of the sheath.4,15 A small left anterior minithoracotomy is required for the puncture of the apex and placement of the sheaths. For the current Edwards-Sapien and Sapien XT valves a ≥ 24 F sheath is needed, and we recently described the new 18 F Certitude delivery system for the transapical placement of the Sapien 3 valve (Fig 1).9 This lower profile sheath might also reduce the occurrence of myocardial tears, myocardial injury, and bleeding.

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Fig 3 – Images of the balloon-expandable valve implantation technique. (A) Deployment of a balloon-expandable Sapien XT valve under rapid pacing. White arrows indicate the balloon during maximal expansion. (B) Fluoroscopic image of an Edwards Sapien XT valve following valve implantation (white arrow). (C) The alignment of the Sapien 3 valve in the aortic annulus confirmed by angiogram, and the central marker was used to better align the prosthesis (white arrow). (D) Final angiographic result of the Sapien 3 valve.

The transapical approach initially accounted for about half of the TAVR procedures performed with the Edwards-Sapien system.16,17 Nowadays, with the use of lower profile devices for the transfemoral approach, about 20–30% of the procedures using balloon-expandable THVs are still performed by the transapical approach.18 Apart from avoiding the passage of the catheter through both the iliofemoral system and the aorta, a possible advantage of this approach is the coaxiality of the valve prosthesis within the aortic annulus, which might help in the positioning of the valve, particularly in those patients with horizontal aorta.19 The main disadvantages are the need for a thoracotomy, greater myocardial injury due to the apical perforation of the left ventricle and the potentially life-threatening bleeding complications associated with myocardial tears during the surgical repair of the apex.20,21 It has been shown that optimal analgesia is of major importance to reduce periprocedural pulmonary complications and improve survival in patients undergoing TAVR through the transapical approach.22

Other approaches Other alternatives to the transapical approach such as the subclavian, transaxillary, and transaortic approaches have

been developed for patients with non-appropriate iliofemoral arteries. Both the subclavian and transaxillary approaches have been used more frequently with the self-expandable valves with comparable short- and mid-term outcomes in relation to the transfemoral approach.23,24 However, the use of the subclavian/transaxillary approach in patients treated with a balloon-expandable THV has been limited to a few cases.25,26 The use of the transaortic approach through a small sternotomy has been proposed more recently as a promising alternative approach with the Sapien valve. 27–29 This approach has the advantages of avoiding the use of large catheters through the iliofemoral system/aortic arch and a ventricular apex puncture. This approach has partially replaced the transapical approach in many centers and interestingly, a fully thoracoscopic approach has been recently described. 30

Implantation technique A balloon aortic valvuloplasty is usually performed prior to balloon-expandable THV implantation (Fig 3). Subsequently, the valve is positioned using fluoroscopy, angiography and transesophageal echocardiography guidance, and valve expansion is obtained by balloon inflation under rapid pacing

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(180–220 bpm) in order to minimize cardiac output and avoid valve embolization during valve deployment (Fig 3). Whereas some studies have reported the usefulness of TEE guidance with no angiography for transapical THV implantation, many centers are currently performing balloon-expandable THV implantation with local anesthesia and no TEE guidance with a high success rate.19,31,32 Also, to allow proper positioning of the valve and minimize the risk of valve mal-positioning, a twostep or a slow balloon inflation technique may be used, in order to partially reposition the valve during its deployment.33,34

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Mortality Overall, the 30-day mortality rate associated with TAVR with balloon-expandable valves has ranged from 3.4 to 14.9% (from 3.3 to 9.6% in patients treated by the transfemoral approach, and from 3.8 to 16.9% in those treated by the transapical approach) (Table 2). A recent meta-analysis including studies with at least 100 TAVR patients, showed that the 30-day mortality rate among 8.692 patients treated with a balloonexpandable valve was 8.1% (transfemoral approach: 6.3%, transapical approach: 10.0%; p < 0.001), which it somewhat lower than the mortality predicted by surgical risk scores.45

Acute and 30-day outcomes Major vascular complications Most patients treated with TAVR to date have been considered either inoperable or at a high risk for SAVR. Such patients tend to be octogenarians and have exhibited a high rate of comorbidities, such as such as coronary artery disease (~ 50%), chronic kidney disease (~50%), atrial fibrillation (~30%), chronic obstructive pulmonary disease (~ 25%) and/or peripheral vascular disease (~ 25%). This great burden of comorbidities led to high risk surgical scores in most TAVR studies, with mean logistic EuroSCORE and STS-PROM scores > 20% and > 8%, respectively.16–18,35–43 The main baseline and procedural characteristics of the patients included in large multicenter TAVR registries using balloon-expandable valves and the randomized PARTNER I and II trials are summarized in Table 1, and the main 30-day results are summarized in Table 2 and Fig 4. The Placement of Aortic Transcatheter Valves (PARTNER) I trial was the first prospective randomized trial on TAVR. The balloon-expandable Edwards-Sapien valve was used for those patients allocated to TAVR therapy. The findings are summarized in Tables 1 and 2, and Fig 4. The PARTNER trial included two distinct cohorts of patients: those considered to be inoperable or cohort B (i.e. co-morbidities leading to a predicted risk of 50% or more of either death within 30 days after surgery or a serious irreversible condition); and those considered to be at high surgical risk or cohort A (i.e. predicted risk of operative mortality ≥15% as determined by site surgeon and cardiologist and/or a minimum STS score of 10).38,40 The PARTNER II trial for inoperable patients compared the safety and effectiveness of the Sapien XT valve vs. the Edwards-Sapien valve in 560 patients.43 Finally, the PARTNER II trial (clinicaltrials.gov, NCT01314313), which completed enrollment in late 2013, will compare the 1-year mortality and stroke rates after TAVR with the Sapien XT valve vs. SAVR in 2,000 patients considered to be at moderate risk (STS score between 4% and 8%). The most frequent complications associated with TAVR and their respective rates in various studies are summarized in Table 2. The Valve Academic Research Consortium (VARC) has recently proposed standardized consensus definitions for important clinical endpoints, including major complications in TAVR, and this has recently been reviewed as the VARC-2 criteria. 46,47 This initiative was of extreme importance in order to establish a more uniform and consistent evaluation of TAVR complications and to allow comparison between studies.

The use of 22/24 F sheaths with the Edwards-Sapien valve was associated with a high rate (>10–15%) of vascular complications, and the more recent use of lower profile balloon-expandable systems such as the Sapien XT and Sapien 3 translated into a significant reduction in vascular complications (20 F THV systems, percutaneous closure has become the standard with the use of smaller systems, and the optimization of the percutaneous closure technique is of major importance in reducing the occurrence of vascular complications associated with the transfemoral approach.14,50

Intraventricular conduction abnormalities The occurrence of new-onset intraventricular conduction disturbances is one of the most frequent complications associated with TAVR.51 While the use of balloon-expandable valves has been systematically associated with a lower rate of conduction disturbances compared to self-expandable valves, the rate of new-onset LBBB in patients without prior pacemaker or conduction disturbances remains as high as ~ 25% following balloon-expandable valve implantation.51,52 However, about half of these conduction disturbances resolve within a few days, and half of those persisting at hospital discharge resolve within the weeks-months following the procedure, which is not the case with self-expandable valves. A larger QRS at baseline and a lower (more ventricular) implantation of the balloon-expandable valves have been associated with a higher rate of conduction disturbances.52 The need for pacemaker implantation following balloonexpandable valve implantation has been nearly systematically

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Table 1 – Main baseline characteristics of patients included in large multicenter TAVR registries and the PARTNER trial.

Study

Type of Study

Large series and registries Registry Belgian35 (n = 328; BEV: 187) Canadian17 Registry (n = 339)

Valve type

Approach

Sapien

TF: 99 TA: 88 TF: 162 TA: 177

Procedural Success (%)

Sapien: 83 ± 6 Sapien: 47

Sapien: 30 ± 16

Sapien: 97.0

All: 81 ± 8 TF: 83 ± 8 TA: 80 ± 8 TF: 83 ± 7 TA: 82 ± 7

All: 93.3 TF: 90.5 TA: 96.1 All: 98.3

Mean Age (y)

Men (%)

Sapien (n = 166)

TF Sapien: 95 TA Sapien: 71

Registry France-237 (n = 3.195; BEV: 2.107)

Sapien (n = 2.107)

TF: 2.361 TA: 567 SC: 184

Sapien: 83 ± 7 Sapien: 46.6

All: 27.7 ± 16.3 TF: 25.8 ± 14.9 TA: 29.4 ± 17.2 All: 25.6 ± 11.4 TF Sapien: 25.6 ± 11.3 TA Sapien: 26.8 ± 11.6 Sapien: 22.2 ± 14.3

PARTNER-EU44 (n = 130)

Registry

Sapien

TF: 61 TA: 69

SOURCE16 (n = 1,038)

Registry

Sapien

TF: 463 TA: 575

All: 82 ± 6 TF: 82 ± 5 TA: 82 ± 6 TF: 82 ± 7 TA: 81 ± 7

All: 44.6 TF: 39.3 TA: 49.3 TF: 44.8 TA: 44.0

All: 30.0 ± 13.7 TF: 25.7 ± 11.5 TA: 33.8 ± 14.4 TF: 25.7 ± 14.5 TA: 29.1 ± 16.3

SOURCE XT18 (n = 2,600) TRAVERCE41 (n = 168)

Registry

Sapien XT

Registry

TF: 82 ± 7 TA: 80 ± 6 All: 82 ± 6

TF: 35.5 TA: 54.4 All: 24.4

TF: 19.9 ± 12.0 TA: 21.8 ± 13.8 All 27.0 ± 12.7

United Kingdom39 (n = 870; BEV: 410)

Registry

CribierEdwards or Sapien Sapien (n = 410)

TF: 1,694 TA: 906 TA: 168

TF: 599 Others: 271

All: 82 ± 7 TF: 82 ± 7 Other routes: 82 ± 7 Sapien: 83 ± 7

All: 52.4 TF: 51.9 Other routes: 53.5 Sapien: 52.9

All: 18.5 (11.7, 27.9) TF: 17.1 (11, 25.5) Other routes: 21.4 (14.4, 33.6) Sapien: 18.5 (12.4, 27.7)

All: 97.2 TF: 97.3 Other routes: 97.1 Sapien: 98.1

Sapien

TF: 244 TA: 104

All: 84 ± 7

All: 57.8

All: 29.3 ± 16.5

NA

Sapien

TF: 179

All: 83 ± 9

All: 45.8

26.4 ± 17.2

98.9

Sapien: (n = 276) Sapien XT (n = 284)

TF: 560

Sapien: 85 ± 9 Sapien: 51.4 Sapien XT: Sapien XT: 84 ± 9 49.6

NA

NA

Sapien (n = 9,560)

TA: 4.888 Transarterial: 4.661

Sapien: 82

Sapien: 24

NA

France36 (n = 244; BEV: 166)

Registry

Randomized trials Randomized PARTNER I40 High-risk cohort-A (n = 348) PARTNER I38 Randomized Nonoperable cohort-B (n = 179) Randomized PARTNER II43 Nonoperable cohort-B (n = 560)

Meta-analysis Khatri et al.45 ⁎ (n = 9,560)

Registries and randomized studies

Sapien

Logistic Euro SCORE (%) [Mean ± SD/ Median (IQR)]

All: 44.8 TF: 56.1 TA: 34.5 TF: 55.9 TA: 64.3

Sapien: 47

Sapien: 97.0 TF: 97.1 TA: 95.9 SC: 96.7 All: 95.7 TF: 96.4 TA: 95.4 All: 93.8 TF: 95.2 TA: 92.7 NA All: 95.8

Abbreviations: BEV, balloon-expandable valve; TF, transfemoral; TA, transapical; SC, subclavian; TAo, transaortic; N/A, data not available; EU, European Union; FRANCE, FRench Aortic National CoreValve and Edwards; EuroSCORE, European System for Cardiac Operative Risk Evaluation; PARTNER, Placement of Aortic Transcatheter Valves; SOURCE, Sapien Aortic Bioprosthesis European Outcome; TRAVERCE, Transapical Surgical Delivery of the Cribier-Edwards Aortic Bioprosthesis. ⁎ Meta-analysis including studies with >100 patients.

100 patients.

Stroke Cerebrovascular events (CVEs) are still among the most troublesome complications associated with TAVR. The mean 30-day major stroke rate in two recent meta-analyses including more than 10,000 patients undergoing TAVR was ~ 3.0%, ranging from 0% to 6.7%.45,54 Of note, in the PARTNER trial (cohort A) the CVE rate (including stroke and transient ischemic attack) was higher in the TAVR than the SAVR group at 30-day (5.5% vs. 2.4%, respectively; p = 0.04) and at 1-year follow-up (8.3 vs. 4.3%, respectively; p = 0.04).40 Also in the non-operable cohort of the PARTNER trial, a higher rate of CVE

at 30-day (6.7% vs. 1.7%, respectively; p = 0.03) and 1-year (10.6% vs. 4.5%, respectively; p = 0.04) follow-up was found among TAVR patients than among those managed conservatively.38 About half of CVEs following TAVR occur within the first 24 hours after the procedure, and mechanical factors such as valve embolization, multiple valve positioning attempts or balloon post-dilation have been identified as predictors of these acute events, whereas other factors such as atrial fibrillation have been associated with a higher rate of subacute (> 24 hours) events.55 No study to date has identified any effect of valve type (balloon-expandable vs. selfexpandable) on TAVR stroke rate. Also, the use of the

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Fig 4 – Mortality rates at 30-day (A), 1-year (B), 2-year (C), and 3-year (D) follow-up of the PARTNER I (non-operable and high-risk cohorts) and PARTNER II (non-operable cohort) trials.

transapical approach has not been associated with a lower rate of clinically apparent or silent stroke following TAVR, despite avoiding the passage of large catheters through the aortic arch and the retrograde crossing of the aortic valve.16,17,56 The use of embolic protection devices during the TAVI procedure and the optimization of antithrombotic therapy may play a major role in reducing the incidence of stroke associated with TAVR procedures.57

Valve malpositioning and embolization The incidence of valve malpositioning/embolization with the balloon expandable valves has been shown to be ~ 1%, similar or even somewhat less than the 2.3% (1.0–4.2%) reported with self-expandable valves.7,45 On the other hand, unlike the case of self-expandable valves, as much as half of balloonexpandable valve embolizations occur towards the left ventricle. This usually requires open-chest surgery and it

has been linked to a high mortality rate.7 Valve malpositioning/ embolization with balloon-expandable valves is generally caused by anatomic and technical factors, which may be avoided with judicious procedural planning.

Coronary obstruction Coronary ostia obstruction is a rare but life-threatening complication of TAVR, with an incidence usually < 1%.58,59 A recent large TAVR series including >6,600 patients showed a global incidence of 0.66% (0.81% for the balloon-expandable THV vs. 0.34% for the self-expandable valves, p = 0.02).59 It is still unclear whether these differences in coronary obstruction rates between valve types are due to differences in the valve stent frame and mechanism of valve implantation or secondary to different recommendation policies according to the manufacturer.59 This complication was also more frequent in women and in patients with prior surgical bioprosthesis.58,59 While PCI was the first revascularization

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attempt in 75% of patients (successful in ~ 80%), urgent CABG and/or mechanical hemodynamic support (including cardiopulmonary bypass) were required in a significant number of patients, underscoring the importance of performing these procedures in highly experienced centers with cardiac surgery facilities. The 30-day mortality rate associated with this complication was as high as 41%.

Late outcomes The 1-year survival rates from the large multicenter TAVR registries with balloon-expandable valves and the randomized controlled PARTNER trial are summarized in Table 2 and Fig 4. Overall, TAVR was associated with a 1-year survival rate ranging from 63.0 to 78.6% (69.3–82.0% for transfemoral approach; 49.3–78.0% for transapical approach). A recent meta-analysis including more than 8,500 patients treated with a balloon-expandable valve showed a mean survival rate of 76.6% at 1-year follow-up (transfemoral approach: 80.2%; transapical approach: 74.7%).45 The survival rates up to 3-year follow-up reported in the PARTNER trial (inoperable and high-risk cohorts) are summarized in Fig 4.60–63 The superiority of TAVR to medical treatment (including balloon valvuloplasty) in non-operable patients at 1year follow-up was maintained and even increased at 3-year follow-up. Also, the non-inferiority of TAVR to SAVR was also maintained up to 3-year follow-up, further confirming TAVR as a valid alternative to SAVR for the treatment of high-risk patients. In addition to the survival results, the PARTNER trial showed significant and similar improvements in functional status and quality of life of TAVR patients as compared to medical treatment and SAVR, respectively.64,65 There are very few data in the literature on the long-term outcomes following TAVR. Rodés-Cabau et al. reported the long-term outcomes of the Canadian multicenter experience including 339 patients.66 After a mean follow-up of 42 ± 15 months, 188 patients (55.5%) had died, 81% of these deaths were late (> 30-day) deaths (non-cardiac: 59%, cardiac: 23.0%, unknown: 18%). The improvement in functional capacity after TAVR was sustained at the latest follow-up, with 89% of the patients in functional class I and II and no cases of structural valve failure during the follow-up period. Additionally, Toggweiler et al. have recently reported the 5-year outcomes of a single-center experience of TAVR including 88 patients treated with the balloon-expandable Cribier-Edwards valve.67 The survival rate at 5-year follow-up was 35%. In these studies, the presence of co-morbidities such as chronic obstructive pulmonary disease, kidney dysfunction, atrial fibrillation or frailty, in addition to suboptimal TAVR results (moderate or severe residual aortic regurgitation/AR) were the predictors of poorer late outcomes.

Valve hemodynamics and durability Even though THVs are expanded without removing the severe calcified native aortic valve, the hemodynamic results following TAVR are usually excellent, with systematic mean

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residual gradients and aortic valve areas of < 15 mm Hg and > 1.5 cm2, respectively.3,5,10,15–17,35–41,68–70 Clavel et al. showed that the hemodynamic results of TAVR (mean gradient, residual valve area) were superior to those obtained with stented and stentless surgical bioprostheses, especially in those patients with small (< 20 mm) aortic annulus.71 In accordance with these results, centrally analyzed echocardiographic data from the PARTNER trial showed that after up to 2 years of follow-up, the peak and mean transaortic gradients were significantly lower in the TAVR group, with larger indexed EOA and less prosthesis-patient mismatch, compared to SAVR.72 However, TAVR patients had significantly more total and paravalvular AR at every post-implantation time than did the patients of the SAVR cohort.72 The presence of residual paravalvular AR is very frequent (~ 70%) following TAVR.66,67,72–74 Although residual AR is ≤ mild in most cases, ~ 10% of patients have moderate to severe residual AR, which in turn has been identified as an independent predictor of acute and late mortality following TAVR. 73,74 Several factors have been associated with the occurrence of moderate or severe AR in patients receiving a balloon-expandable valve. Apart from those cases of significant AR associated with valve malpositioning, the amount of calcium of the native aortic valve, the presence of a larger aortic annulus, and an inappropriate aortic annulus sizing leading to an undersized valve prosthesis have been identified as the main predictors of significant residual paravalvular AR. 75–78 The use of computed tomography 3dimensional measurements of the aortic annulus for balloon-expandable THV sizing has been shown to reduce the incidence of significant residual AR.79 Also, a valve type effect with a lower rate of significant aortic regurgitation associated with balloon-expandable (vs. self-expandable) valve has been suggested by several studies.37,74,80,81 Further research is also needed to improve THV technology in order to reduce the incidence and severity of paravalvular leaks following TAVR.72,76,79 In this regard, the new balloonexpandable Sapien 3 system, with an additional outer skirt to potentially reduce paravalvular AR has been associated with promising preliminary results.8,9 While data on THV durability remain scarce, some studies have evaluated the hemodynamic changes of balloon-expandable valves at long-term follow-up. RodésCabau et al. showed the lack of significant hemodynamic or structural deterioration at 4-year follow-up in the Canadian experience (central echo core lab data); and Toggweiler et al. reported similar results at 5-year follow-up, with a minimal average decrease in mean aortic valve area (0.06 cm 2/y) and an increase in mean transvalvular gradient (0.27 mm Hg/y).67 Importantly, no cases of structural valve failure were observed at 5-year follow-up. Also, the presence and degree of paravalvular and transvalvular residual AR remained stable at longterm follow-up.38,40,72 Several cases of balloon-expandable valve restenosis, presumably secondary to valve thrombosis, have recently been reported.82,83 The use of anticoagulation therapy has been successful in most of these cases and this treatment should probably be used systematically before deciding to explant the transcatheter valve prosthesis.82,83

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Fig 5 – Images of newer balloon-expandable valves. (A) Inovare (Braile Biomedical, São José do Rio Preto, Brazil). (B) Colibri THV (Colibri Heart Valve, Broomfield, USA).

Other balloon-expandable technologies The Innovare balloon expandable system consists of a trileaflet bovine pericardial valve mounted in a cobalt-chromium alloy, and is available in 4 sizes—20, 22, 24, and 26 mm (Fig 5). The valve is implanted through the transapical approach, and the first-in-man cases were performed in 2009.84 A more recent larger series of patients showed the feasibility of the TAVR procedure with this THV with a success rate of 91% (30/33). The 30-day and 1-year mortality rates were 18.2% and 39.5%, respectively.85 The valve hemodynamics at hospital discharge showed some degree of AR in 10 patients (30.3%), and the peak and mean gradients at 1-year follow-up were 21.3 ± 12.4 mm Hg and 10.5 ± 6.9 mm Hg, respectively. Another balloon-expandable valve with still limited clinical data is the Colibri THV (Colibri Heart Valve, Broomfield, USA; Fig 5). This is a low-profile (14-F) premounted, pre-crimped, and pre-packaged ready-for-use TAVR system. The valve is made of three independent pieces of porcine pericardium, which are created using a unique folding method. The folded design of the leaflets, which are sewn into a stainless steel laser cut frame, reduces the amount of material in the frame. The first implant was performed in November 2012 and a feasibility study is planned soon.86

Conclusions Since the pioneering experience in 2002, the balloonexpandable THV technology has played a major role in the development of TAVR in the last decade. TAVR has since been established as the standard of care for patients with severe symptomatic AS who are considered inoperable, and as an alternative treatment option to SAVR in those patients considered at high risk. Future improvements in THV technology (ex. implementation of anti-paravalvular leak properties) and the demonstration of its efficacy (compared

to that of SAVR) in lower risk patients should lead to a significant expansion of TAVR in the near future.

Acknowledgments H.B.R. is supported by a research PhD grant from “CNPq, Conselho Nacional de Desenvolvimento Científico e Tecnológico – Brasil”. I.A.S. received a grant (Rio Hortega contract) from the Instituto de Salud Carlos III, Madrid, Spain.

Statement of Conflict of Interest Dr Josep Rodés-Cabau is consultant for Edwards Lifesciences and St. Jude Medical. All other authors declare that there are no conflicts of interest.

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