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| REVIEW ARTICLE |
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| Year : 2015 | Volume
: 3
| Issue : 1 | Page : 3-7 |
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Transcatheter Aortic Valve Implantation Emerging as Good Alternative to Surgery for Aortic Stenosis- Present Status
Edgar Tay
Consultant Cardiologist, Department of Cardiology, National University Heart Centre, Singapore
| Date of Web Publication | 14-Mar-2015 |
Correspondence Address:
Edgar Tay
National University Heart Centre
Singapore
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/2321-449X.153278
The advent of transcatheter aortic valve implantation (TAVI) has allowed many patients with severe aortic valve stenosis who were previously deemed too high risk or inoperable to be effectively treated. Keywords: Transcatheter aortic valve implantation, aortic valve replacement, aortic stenosis
How to cite this article:
Tay E. Transcatheter Aortic Valve Implantation Emerging as Good Alternative to Surgery for Aortic Stenosis- Present Status. Heart India 2015;3:3-7 |
How to cite this URL:
Tay E. Transcatheter Aortic Valve Implantation Emerging as Good Alternative to Surgery for Aortic Stenosis- Present Status. Heart India [serial online] 2015 [cited 2023 Mar 22];3:3-7. Available from: https://www.heartindia.net/text.asp?2015/3/1/3/153278 |
| Introduction | |  |
The advent of transcatheter aortic valve implantation (TAVI) has allowed many patients with severe aortic valve stenosis who were previously deemed too high risk or inoperable to be effectively treated.
| Historical development | | |
The development of percutaneous valve therapies had begun with Andersen et al. [1] in 1992 when he implanted a porcine based valve attached to a metal stent in a porcine model. This showed good hemodynamic outcomes and established the feasibility of a balloon expandable aortic valve. One decade later, Dr. Alain Cribier described the first percutaneous aortic valve implantation human using an antegrade approach. [1] This technique was feasible, but was technically demanding and difficult to reproduce. The retrograde technique was subsequently devised by Webb et al. and is now the dominant method of delivering the aortic valve to the native aortic valve leaflets. [2] However, patients who had small femoral arteries or significantly obstructive atherosclerotic disease could not be treated through the femoral route. As a result, alternative access sites had to be developed. The second most common access site is the transapical access. [3] In this route, a small thoracotomy was made near the apex of the heart and the valve was delivered via the apex of the heart through the native aortic valve leaflets. Newer access sites that have been explored include the transaortic and subclavian access.
| Types of valves available | | |
The current generation of valves being used has undergone several changes. There are 2 major valves available, which are currently in commercial use. The 2 dominant valve systems are a balloon expandable system or a self-expanding type [Figure 1]. | Figure 1: Two types of transcatheter heart valve systems currently: The Edward SAPIEN XT (a) valve (balloon expandable) or self-expanding Corevalve (b)
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The predominant balloon expandable valve is the Edward SAPIEN or SAPIEN XT (Edward Lifesciences LLC, Irvine, California). The first iteration started off with equine pericardial valve leaflets mounted on a stainless steel stent. This was later changed to a bovine pericardial valve, and the latest iteration is bovine pericardial valve leaflets mounted on a cobalt chromium stent (Edward SAPIEN XT). This has allowed the valve to be crimped into a smaller profile. The Edwards valves come in 3 sizes of 23 mm, 26 mm and most recently 29 mm.
The Corevalve (Medtronic Inc., Minneapolis, Minnesota) is the most commonly used self-expanding valve. This is a nitinol based valve with trileaflet porcine pericardial valve leaflets. It too has 3 valve sizes of 26, 29 and 31 mm.
There are numerous other valves that are being developed. These newer generation valves aim to be smaller in profile, reduce paravalvular regurgitation and to be retrievable (that is, can be removed and redeployed after the valve has been fully expanded).
| Delivery systems and techniques in transcatheter aortic valve implantation | | |
Transfemoral systems
This procedure is commonly done under general anesthesia with transesophageal echocardiography guidance.
Percutaneous access is first obtained via the right or left common femoral artery. Previously, surgical cutdowns were made to provide direct access, but currently, vascular closure devices such as the Proglide or Prostar XL device (Abbott Vascular, Redwood City, CA) are used to provide a totally percutaneous procedure. These are suture closure devices, which place sutures in the arteriotomy site and allow closure of the site at the end of the procedure. The Edwards sheath sizes were initially 22Fr (all sizes reflect the internal diameter) and 24Fr and more recently reduced to 18Fr and 19Fr to accommodate the 23 and 26 mm valves (the 29 mm valve is delivered via the transapical procedure currently) respectively. The Corevalve system also utilizes an 18Fr sheath for both the 26 mm and 29 mm valves.
During TAVI, the aortic valve is first crossed with an Amplatz 1 catheter and a straight tipped wire. This is then exchanged for a preshaped curved Amplatz extrastiff wire, which allows subsequent devices to be delivered to the native aortic valve without risk of injury to the myocardium. Next, balloon aortic valvuloplasty is performed under rapid ventricular pacing. This serves to reduce cardiac output for effective valvuloplasty. The balloon expandable valve is then delivered across the native valve leaflets, positioned and then deployed under rapid ventricular pacing [Figure 2]. The self-expanding Corevalve is also positioned in the same fashion, but this valve can be expanded without rapid ventricular pacing. | Figure 2: Transfemoral transcatheter aortic valve implantation. Initial assessment of the optimal implantation view (a). This is followed by crossing the aortic valve and performing balloon aortic valvuloplasty under rapid ventricular pacing (b). The delivery system enables the transcatheter valve to be positioned to the area of the native aortic valve annulus (c and d). Rapid ventricular pacing is again performed and the valve is expanded (e). Final result is good with full expansion of the transcatheter heart valve (f)
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Transapical system
This is done by first performing a thoracotomy. After which an apical aspect of the left is identified. A box type or circular purse-string type suture is first created before the entry into the left ventricle. The aortic valve is crossed, and an Amplatzer extrastiff wire is positioned with its tip in the descending aorta. A 14Fr sheath is first placed through which balloon valvuloplasty is performed under rapid pacing. This is then exchanged with the transcatheter sheath. The Edward SAPIEN valve can then be delivered antegrade to the native aortic annulus and then deployed under rapid ventricular pacing [Figure 3]. The delivery system and stiff wire is carefully removed, and the apex is repaired. | Figure 3: Transapical transcatheter aortic valve implantation. A 14Fr sheath is positioned in the left ventricular apex (a) through which balloon aortic valvuloplasty is performed (b). The transcatheter valve is delivered to its intended site (c) and then expanded under rapid ventricular pacing (d)
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Clinical data
Edwards valve
Randomized trials
The PARTNER trial cohort B was published 2 years ago. [4] This trial recruited patients who were deemed surgically inoperable (defined as the presence of co-existing conditions that would be associated with a predicted probability of 50% or more of either death by 30 days after surgery or a serious irreversible condition-this required 2 cardiac surgeons to agree). The trial compared the transfemoral implantation of an Edward SAPIEN heart valve versus standard treatment (medications with or without balloon aortic valvuloplasty) in 358 patients. This landmark trial demonstrated a clear benefit of TAVI over standard therapy with 1-year rate of death to be 30.7% versus 50.7%.
The PARTNER trial cohort A trial was subsequently published. [5] This trial assessed 699 patients who were deemed to be at high surgical risk (defined as an STS score of >10%). The patients were than assessed if they could undertake a transfemoral or transapical procedure. After this patient would then be randomized to surgery or a transcatheter procedure. The PARTNER cohort a trial met its hypothesis that TAVI was noninferior to surgery with a 1-year death rate of 24.2% versus 26.8%.
These 2 trials were unique in that the operators were still in the learning curve of the procedure. In addition, the larger 22 or 24Fr sheath were utilized in the study.
In recent years, the 2 years follow-up study of the PARTNER trial cohort A showed no significant difference in the rates of death at 2 years with maintenance of valve areas and gradients. [6]
Registry data
The Edward SAPIEN Aortic bioprosthesis European outcome (SOURCE) registry was designed to assess initial post commercial clinical TAVI results of the Edward SAPIEN valve in consecutive patients in Europe. 1038 patients were followed-up for 1-year. Overall 1-year survival was 76.1%. Three-quarters of surviving patients were in New York Heart Association class of I or II. [7]
Although the SOURCE registry assesses patients implanted with the larger 22 or 24Fr systems, the current system used in Europe is the SAPIEN XT valve with the 18Fr Novaflex systems. A recent presentation at the EuroPCR meeting in May 2012 reported the initial 30 days results. 1694 patients were treated with the transfemoral system with a mortality rate of 4.3%. The mortality rate of the non transfemoral routes (transapical, transaortic and trans-subclavian) was 9.7%.
Corevalve
The US pivotal trial and the SURTAVI trial are currently recruiting. The US pivotal trial is a randomized controlled trial to compare extremely high risks patients (predicted mortality or serious irreversible morbidity of >50%) and high-risk patients (predicted mortality ≥15%, but <50% risk of 30 days death or serious irreversible morbidity) to conventional heart surgery. The SURTAVI trial aims to assess the safety and efficacy of the Corevalve in AS patients with intermediate surgical risks (defined as surgical mortality ≥3% and ≤8%).
Advance registry
This registry consists of 1015 patients who were consecutively treated at 44 experienced centers. Recent presented survival rates were 95.5% at 30 days and 87.2% at 60 days.
Importance of the heart team
The TAVI revolution could only have been successful because of the close collaboration between surgeons and cardiologist. A typical heart valve team consists of cardiac surgeons, interventional cardiologists, echocardiologists, radiologists and anesthetists. Such teams often discuss cases to determine the suitability of treatment and the optimal access site. The ACC/AHA/STS has published on the importance of such a team in TAVI. [8],[9]
Current challenges
Paravalvular regurgitation
Recent studies have shown that paravalvular regurgitation is common after TAVI. Approximately 40-50% of patients have mild regurgitation and up to 7-15% of patients could have moderate or more degrees of leak. [10],[11],[12] A recent study showed that even mild degrees of aortic regurgitation were associated with increased mortality. These design limitations of the current iteration of transcatheter heart valve is due to incomplete circumferential apposition of the prosthesis with the annulus [Figure 4]. The factors associated with paravalvular regurgitation are related to the size of the annulus, the degree of calcification and the position of the prosthetic heart valve. There have been improvements made by sizing more accurately with computed tomography (CT) as well as improvement in the newer generation of transcatheter heart valves. | Figure 4: Paravalvular regurgitation post transcatheter aortic valve implantation
Click here to view |
Stroke risks
The risk of stroke has been noted to be higher in patients who undergo TAVI compared with conventional open heart surgery. This finding was noted in the published PARTNER trial results. A recent metaanalysis involving >10,000 patients showed that the average risk of procedural stroke was 1.5%, the risk of strokes or transient ischemic attacks (TIA) at 30 days was approximately 3.3% and the transapical approach appeared to be associated with a lower risk of stroke. Importantly, the risk of mortality increased 3½ times in these patients compared to those without stroke. [13] It has been reassuring to note that there is no late stroke hazard (>30 days of the index procedure), and this has been published in a longer 2 years follow-up study of the PARTNER trials.
Newer technologies on the horizon
Smaller profile delivery systems
There are continued attempts to reduce sheath and delivery catheter size as this has been associated with a reduction in major vascular complication. There are several new sheaths and delivery systems being developed, which may allow patients with smaller vessel sizes to be treated.
Retrievable and repositionable valves
Retrievable and repositionable transcatheter valves allow adjustment and optimization of the valve position during deployment. Several second generation valves are being developed which incorporate this feature.
Newer access sites
While the transfemoral and transapical access sites were the original and most common sites used to deliver the transcatheter heart valves, other sites being explored include the subclavian artery (Corevalve) as well as the transaortic route. These access sites have shown to be equally effective at delivering and deploying the transcatheter valves.
Embolic protection devices
The increased risk of stroke or TIAs following TAVI has been postulated to be due to increased liberation of embolic debris towards the intracranial circulation. Transcranial Doppler studies have demonstrated these effects at various stages of the procedure. Embolic protection devices [Figure 5] such as deflectors that are positioned across the aortic arch or filter placed in the carotids aim to deflect or trap embolic debris in an attempt to reduce stroke. [13],[14],[15] The efficacy of one such filter would be assessed in the PROTAVI trial in Europe.
Newer imaging systems
The development of advanced imaging systems has allowed a safer and more effective TAVI procedure. These include the better utilization of three-dimensional CT assessment of annulus size, and this may aid in better valve sizing and translate to reduce paravalvular regurgitation. [16],[17] A better understanding of the annular planes have also aided in better positioning of the transcatheter heart valve before deployment. Several imaging systems allow visualization of the valve plane and optimizing the best angle of implantation.
| Conclusion | | |
The advent of TAVI has been described by Carabello as one of the most exciting aspects of cardiology in this era. [18] The technique has allowed more patients who were previously deemed unsuitable or too high risk for surgery to undergo treatment. With improvement in patient selection, operator experience, refinement in techniques and devices over time, the results of TAVI are likely to improve.
| References | | |
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| 17. | Willson AB, Webb JG, Labounty TM, Achenbach S, Moss R, Wheeler M, et al 3-dimensional aortic annular assessment by multidetector computed tomography predicts moderate or severe paravalvular regurgitation after transcatheter aortic valve replacement: A multicenter retrospective analysis. J Am Coll Cardiol 2012;59:1287-94. |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
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