Conventional Aortic Valve Surgery (Open Surgical Approaches)

Chapter 24

Conventional Aortic Valve Surgery (Open Surgical Approaches) Kaan Kırali, Özge Altaş Yerlikhan Koşuyolu Heart and Research Hospital, Istanbul, Turkey

Chapter Outline Introduction257 Historical Perspective 257 Indications258 Conventional Aortic Valve Replacement 259 Incision259 Full-median Sternotomy (Standard Sternotomy) 260 Mini-median Sternotomy Techniques 261 Mini-Partial Sternotomy Techniques 262 Mini Thoracotomy Techniques 263 Endoscopic Interventions 264 Cardiopulmonary Bypass/Myocardial Protection 264 Aortotomy265 Transverse Aortotomy 265 Total Aortotomy 265 Oblique S-shape Aortotomy 265 Oblique Longitudinal Aortotomy 265 Reverse-U-aortotomy (Kırali Incision) 265

Valve Resection 267 Selection of Prosthesis-type 268 Position of Prostheses 268 Techniques for Suture Insertion 268 Stented Valves 268 Stentless Valves 269 Sutureless Valves 270 Outcomes270 Operative Mortality and Survival 270 Stroke272 Complete Heart Block 272 Postoperative Complications 272 Anticoagulant-Related Late Complications 272 Structural Valve Degeneration 273 Future273 References273

INTRODUCTION The aortic valve is situated in the middle top of the valve region, which is enclosed by the other three heart valves. This anatomic configuration makes the aortic valve easier to reach, handle, and intervene through aortotomy in conventional open-heart surgery, or during surgery on the other valves. There are several predictors for developing aortic valve pathologies but the natural risk factor of aging itself can seriously affect the aortic valve. The functional anatomy of the aortic valve is influenced not only by leaflets but also by the three dimensional shape of the aortic root, which sometimes leads to procedural mistakes by less experienced cardiac surgeons. Additionally, errors in accounting for the three-dimensional shape of aortic leaflets are the most frequent of coaptation defects due to destroyed structure or unsatisfactory surgery. Aortic valve diseases resulting in significant diagnostic signs with or without symptoms require invasive treatment options such as aortic valve replacement (AVR), repair, or transcatheter aortic valve implantation (TAVI). The last two procedures are the subject of the next chapters; therefore, we only describe here the conventional AVR technique.

HISTORICAL PERSPECTIVE Surgical AVR was one of the first open conventional heart operations, and several types of prostheses have been introduced into practical use. The first mechanical valve was a caged-ball valve implanted by Harken and colleagues [1] in 1960. Later, the development of the tilting disc valves occurred in the second half of 1960s [2,3] and 1970s [4]. The final major development in AVR was the bileaflet design introduced at the end of 1970s, which is currently accepted as the gold standard for mechanical prostheses [5]. The design is excellent for long-term freedom from structural degeneration, and pyrolytic carbon is the strongest material against any prosthetic-leaflet complications [6]. New Approaches to Aortic Diseases from Valve to Abdominal Bifurcation. http://dx.doi.org/10.1016/B978-0-12-809979-7.00024-9 Copyright © 2018 Elsevier Inc. All rights reserved.

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The first bioprostheses was a porcine xenograft aortic valve preserved with formaldehyde and implanted into the aortic root in 1965 [7]. But the modern bioprosthetic valve field was started after Carpentier and colleagues [8] introduced glutaraldehyde to prevent early structural failure. The first step is the introduction of glutaraldehyde-treated stented bioprostheses, which are made from “a porcine aortic valve” or “porcine or bovine pericardial (tissue) fashioned into a three-cusp valve” mounted on a rigid stent, which allows their use in isolated AVR procedure. The second step is zero pressure fixation, which preserves the collagen architecture and natural elastic behavior for stress reduction on the leaflets. The third step is the antimineralization treatment for prevention of tissue calcification and calcific degeneration. Stentless bioprosthetic valves were developed in the 1990s for better hemodynamics due to the prevention of patient– prosthetic mismatch (PPM) as well as longer durability due to better stress distribution but the true first stentless tissue valves were the homografts used in the 1960s. However, those early homograft tissue valves were not very durable and neither did they exhibit the hemodynamic improvements seen with newer generation stented bioprostheses [9]. Sutureless or transcatheter bioprostheses have been used more often than stentless bioprostheses due to their ease of implantation, shorter procedural time, availability of minimal invasive procedures, and a shorter procedural learning curve in the last decade. Older age, increasing comorbidities, higher risk profiles for conventional surgery, and improved results all contribute to the popularity and success of sutureless bioprostheses versus stented or stentless biologic valves for isolated or combined AVR operations, and especially in porcelain aorta or replacement of prior implantation of stentless tissue valves [10].

INDICATIONS Surgical AVR is the gold standard for significant aortic stenosis (AS), especially with severe calcification. According to both American [11] and European [12] guidelines, early surgical AVR is essential for symptomatic severe AS (mean transvalvular gradient ≥ 40 mmHg; maximal aortic velocity ≥ 4 m/s; effective orifice area ≤ 1 cm2 or 0.6 cm2/m2) or asymptomatic severe AS (mean transvalvular gradient ≥ 50 mmHg; aortic velocity ≥ 4 m/s; effective orifice area ≤ 1 cm2; severe leaflet calcification decreasing systolic opening; left ventricular hypertrophy ≥ 1.5 cm; left atrial dimension ≥ 4 cm) independent from left ventricular ejection fraction (LVEF) to prevent sudden death and heart failure. Asymptomatic moderate AS (mean transvalvular gradient 30–50 mmHg) should be simultaneously treated by surgical AVR during a principal cardiac surgery for treatment of coronary artery, other valvular or aortic diseases. The simultaneous management of mild AS (15–30 mmHg) is controversial during principal cardiac surgery because despite the risks of complication during a future open-heart surgery it has failed to show any survival benefit of an earlier prophylactic AVR [13]. The morbidities related to a prosthetic valve used for the prophylactic AVR or surgical risks related to the reoperation for AVR after coronary artery bypass surgery (CABG) are conflicting, which makes it difficult for cardiac surgeons to decide which strategy is better for their patients. If echocardiographic data reveal significant calcification on the leaflets, and life expectancy is longer than 5 years, a prophylactic AVR can be chosen; however, TAVI might be the best approach while postponing an earlier intervention [14]. The special subgroups of severe AS should be evaluated by dobutamine stress echocardiographic examination preoperatively to determine whether severe AS with 3L can also benefit from surgery: with a low effective orifice area (i.e., ≤1 cm2 or ≤ 0.6 cm2/m2), a low transvalvular gradient (i.e., <40 mmHg), and a low maximal aortic velocity (<4 m/s) [15]. True-severe AS (3L-2L) associated with a low flow state (i.e., stroke volume index < 35 mL/m2 or cardiac index < 3 L/ min/m2) and a depressed LVEF (<50%) should be differentiated from pseudosevere AS, which can be associated with irreversible heart failure and which will not benefit from surgical treatment. The response of the left ventricle against dobutamine stress echocardiography is helpful in identification of this pathology, and peak stress cut-point values on the true-severe stenotic aortic valve should be unchangeable (transvalvular gradient ≥ 40 mmHg; effective orifice area ≤1 cm2; absolute increase in effective orifice area ≤0.3 cm2; maximal aortic velocity ≥ 4 m/s) at all dobutamine levels. Paradoxical severe AS (3L-1L-1N) associated with a low flow state, but a preserved LVEF (≥50 mmHg) develops as a result of left ventricular concentric hypertrophy, but this scenario results in a restrictive physiology and may increase operative risks, especially the risk of PPM due to small aortic annulus with or without small aortic root [16]. This should first be differentiated from pseudosevere stenosis, and the preferred treatment option is one without stented valves. Pseudonormal severe AS (3L-2N) associated with preserved LVEF and normal flow has a lower transvalvular gradient than expected due to measurement errors, small body size or prolonged left ventricular ejection phase, and the transvalvular gradient > 30 mmHg associated with a small effective orifice (≤1 cm2) is accepted as true-severe AS. Despite the similar postoperative transvalvular gradient in this subgroup, surgical AVR or TAVI is associated with better survival than medical therapy [17].

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Surgical intervention is also the gold standard for severe aortic regurgitation (AR), with salvage of the aortic valve the first goal of every surgical technique. Aortic valve repair or aortic valve sparing procedures aim to preserve native aortic leaflets with full anatomophysiologic structure, avoiding any prosthetic material. Surgical AVR must be always the second choice, and preferred only if repair techniques are ineffective. Severe AR (vena contracta > 0.6 cm; effective regurgitant area ≥ 0.3 cm2; regurgitant volume ≥ 60 mL; regurgitant fraction ≥ 50%) with any sign of left ventricle deterioration [LVEF < 50%; left ventricular end-diastolic dimension (LVEDD) > 6.5 cm; left ventricular end-systolic dimension (LVESD) > 5 cm] should be corrected regardless of symptoms, whereas symptomatic severe AR should be corrected regardless of left ventricular systolic function. There are two controversial issues: asymptomatic severe AR with preserved, dilated left ventricle, or with severely impaired left ventricle. Because severe AR is a chronic pathology resulting in left ventricular compensatory dilatation and hypertrophy, preserved LVEF prevents symptoms for a long time. On the other hand, preservation of postoperative LVEF is more effective if the operation is performed with near normal preoperative LVEF. Despite American and European guidelines, surgical intervention for asymptomatic severe AS should be considered when there is normal LVEF (≥50%) and progressive left ventricular dilatation (LVEDD > 6.5–7 cm), implementing a surgical cut-off limit of the LVEDD of <8.1 cm with satisfactory postoperative prognosis for young patients with normal left ventricle function (LVEF > 55%) [18]. However, indexed LVESD (≥2.5 cm/m2) and LVEDD (≥3 cm/m2) can be more often associated with late survival than LVEF level [19]. Asymptomatic moderate or severe AR should be corrected during any principal cardiac surgery such as CABG.

CONVENTIONAL AORTIC VALVE REPLACEMENT Conventional AVR is still the gold standard and remains the most widely preferred approach because of its simplicity and excellent exposure. The standard operation is performed through the full median sternotomy under extracorporeal circulation and cardioplegic arrest. The aortic valve is removed under direct exposure and a prosthetic valve is anchored in the aortic annulus with various suture techniques. Several minimal invasive approaches have been developed to decrease the invasiveness of this conventional approach via mini incisions, epidural anesthesia, new devices, and hybrid procedures [20–22]. The main prerequisites of these minimal invasive techniques are to guarantee adequate exposure, ensure satisfactory handling, decrease trauma, and should be easily taught, widely used, and with improved results compared to the conventional surgery. Despite the use of sutureless valves, which are anchored in the aortic annulus without the use of surgical sutures, all young cardiac surgeons should learn all types of suturing techniques for stented and stentless aortic prostheses, in addition to annular enlargement procedures to avoid PPM. For that reason, surgeons interested in learning and performing minimally invasive AVR need to have expertise in conventional surgery and be in practice at centers with adequate case volumes [23]. Heavy calcification on the aortic valve and/or annulus can complicate the AVR due to difficulties during resection, prosthesis selection, and suturing [24]. It is also important to consider preoperative predictors for adverse outcomes, especially those avoidable risk factors such as hypercholesterolemia [25]. The conventional AVR is performed under general anesthesia with endotracheal entubation. In order to minimize the side effects of general anesthesia, awake open-heart surgery has been developed as a new and unique approach in cardiac surgery. Awake on-pump cardiac surgery offers several advantages over general anesthesia, including absence of tracheal intubation, reduced stress response, lower postoperative arrhythmias, and improved pulmonary outcome [26]. This approach seems more beneficial and safer than conventional anesthesia in patients with chronic obstructive pulmonary disease who are frequently rejected for cardiac surgery [27]. Utilizing this approach with mini-sternotomy techniques may result in outcomes that are better than standard full median sternotomy [28].

Incision Several alternative surgical approaches can be used during conventional AVR to obtain earlier mobilization, better cosmetic results, and lower postoperative pain (Table 24.1). The conventional approach is a midline skin incision with a full median sternotomy extending from the suprasternal notch to just below the xiphoid process. When making the skin incision during reoperations, it is not necessary to excise the previous scar unless it will not be removed. However, in recent years different minimal invasive sternotomy or thoracotomy approaches have been popularized to decrease surgical trauma and to minimize the invasivity of cardiac surgery, especially when using sutureless valves. More recent studies show that minimal invasive surgery is as safe and efficacious as the conventional AVR despite longer cardiopulmonary bypass (CPB) and cross-clamp times. Different minimal invasive approaches also have similar outcomes [29].

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TABLE 24.1  Incisional Approaches for Surgical Aortic Valve Replacement 1. Full sternotomy techniques a. Standard access (full skin incision) b. Minimal access (limited skin incision) 2. Mini-sternotomy techniques a. upper reverse-T-type (sternomanubrial-limited sternotomy) b. upper V-type (manubrium-limited sternotomy) c. lower T-type 3. Partial sternotomy techniques a. upper J-shaped sternotomy (or mirror-L-shaped) b. lower reverse-J-shaped sternotomy (or reverse-mirror-L-shaped) c. reverse-C-shaped sternotomy 4. Thoracotomy techniques a. right anterior (parasternal) thoracotomy b. right anterolateral thoracotomy c. right infra-axillary thoracotomy 5. Endoscopic approaches a. total endoscopic b. port access c. robot assisted

FIGURE 24.1  Full median sternotomy through midline skin incision. (A) Full midline skin incision from the suprasternal notch to the tip of the xiphoid process. (B) Limited midline skin incision from the sternomanubrial junction (the angle of Louis) to the sternoxiphoid junction.

Full-median Sternotomy (Standard Sternotomy) This technique is the gold standard for the conventional AVR. It was first described in 1897 by Milton [30] for the removal of lymph nodes and reintroduced by Julian [31] in 1957 into cardiac surgery due to its simple secure and surgical speed. There are two approaches to access the sternum: use of a full or limited midline skin incision (Fig. 24.1). The limited skin incision preferred for its cosmetic advantages is started at the level of the sternal angle of Louis or 2 cm below and extended down a minimum 4–5 cm. The midline division of the sternum is performed at full length using a standard sternal saw with a vertical blade in first sternotomies, but an oscillating saw should be used for repeat sternotomies. Avoidance of asymmetric division, entry into the neighboring cavities, and innominate vein injury is essential to obtain complication-free surgical procedure outcomes. Keeping pleural cavities intact are also necessary to maintain spontaneous ventilation if awake cardiac surgery is performed. Following full sternotomy, the pericardium is divided and supported with traction sutures to obtain the utmost exposure of the total mediastinum, and all cannulae are inserted as in the standard practice.

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Repeat sternotomies carry several risks such as right atrial and/or ventricular tear, innominate vein injury, or aortic entry. After skin incision, all previous wires at the sternum are divided and removed because they cannot help to prevent any cardiac injury. The best approach is to elevate both sides of the sternum with clamps and to carefully perform the sternotomy. The dissection of fibrous adhesions under the sternum is started with a low setting electrocautery blade at the xiphoid and extended up to the jugulum. After adequate dissection, the redo-sternal retractor can be safely positioned and opened. The next step is the identification and exposure of an adequate space on the distal ascending aorta (or aortic arch) and of the right atrial appendage (or free atrial wall) for cannulation. After cannulation, only limited dissection around the ascending aorta is necessary for cross-clamp and aortotomy incision, and the rest of the heart should remain untouched.

Mini-median Sternotomy Techniques Upper Reverse-T-type (Sternomanubrial-Limited Sternotomy) This technique is best suited for isolated AVR with or without “ascending aorta and/or aortic arch replacement” in patients of all ages [32]. Because this approach can be applied easily, similar to the full median sternotomy, it becomes the best option for patients with impaired respiratory function or awake AVR. For patients with previous cardiac operation undergoing reoperative AVR, this approach (as well as the J-shaped approach) is a feasible and a safe procedure, similar to conventional full sternotomy [33]. An oscillating saw with a narrow blade is more suitable for the vertical division in the midline of the sternum from the sternal notch to the third intercostal space. Next, the sternum is transversely divided to make a reverse-T without mobilization or ligation of the internal thoracic arteries (Fig. 24.2A). A small sternal spreader is used to expose the upper pericardium above the aorta. This approach allows for a visualization of the aortic root, the pulmonary artery, and the superior vena cava, whereas the right atrial appendage can be left under the sternum; however, it is easy to pull it into the operative field. All cannulae can be inserted through this incision as in the standard practice. Upper V-type (Manubrium-Limited Sternotomy) This technique is similar but more limited than upper reverse-T type and helps to avoid a transverse sternal division through the third intercostal space [34]. An oscillating saw with a narrow blade is more suitable for the division of the sternum, which is started from the sternal notch and extended vertically to the level of the third costo-sternal junction. Next, transverse incisions on both sides are started at the second intercostal space just at the sternal edge (parasternally) and the sternum is obliquely divided to make a V-shape incision (Fig. 24.2B). This approach gives an adequate visualization of the entire ascending aorta as well as the aortic valve; but it is an inadequate space for simultaneous cannulations and aortic valve surgery. All cannulations are preferentially performed through peripheric vessels due to the restricted incisional area, but only arterial cannulation can be performed through the aortic arch [35].

FIGURE 24.2  Ministernotomies through midline skin incision. (A) Upper reverse-T-type (sternomanubrial-limited sternotomy). (B) Upper V-type (manubrium limited).

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Lower T-type (Manibrium-Intact Sternotomy) This technique is similar to standard full sternotomy technique with the exception of leaving an intact manubrium. A limited skin incision can be chosen if an oscillating saw is used, otherwise the skin incision should be extended to the tip of the xiphoid to place a standard saw with vertical blade under the sternum. The sternum is divided transversely at the second or third intercostal space, and then the lower part of the sternum is divided vertically in the midline, leaving the upper half of the sternum intact [36]. This approach achieves an adequate view of the aortic root and the whole heart, but it is not possible to reach aortic arch and therefore this approach is seldom preferred for minimal invasive AVR. All cannulations are performed in a routine manner through this incision.

Mini-Partial Sternotomy Techniques Upper J-shaped (or Mirror-L-shaped) This technique is a well-known approach used worldwide. The sternum is divided vertically in the midline from the suprasternal notch down to the level at the third or fourth intercostal space, and then to the right using a standard sternal saw, leaving the upper-left half and the lower part of the sternum intact (Fig. 24.3A) [37]. It is also well suited for primary isolated AVR with or without “aortic root replacement” in patients of all ages barring presence of a porcelain aorta, but the aortic arch surgery is very difficult. This approach allows an adequate exposure of the whole aortic root and vena cava superior, but if the incision is extended to the fourth intercostal space the upper half of the right atrium comes into the operative field [38]. Lower Reverse-J-shaped (or Reverse-Mirror-L-shaped) This technique is often preferred for other cardiac operations but it can be also useful for direct access of the aortic root. The sternum is divided vertically in the midline from the xiphoid to the level of the right second intercostal space, and then to the right using a standard sternal saw, leaving the manubrium, and the lower-left half of the sternum intact (Fig. 24.3B). This approach allows an adequate exposure of the whole heart with the exception of the aortic arch. Reverse C-shaped (Right Sided Partial Sternotomy) This technique is not often favored because the technique is more complicated than the alternatives. After the limited midline skin incision is performed, two parallel incision are performed in the sternum with the use of an oscillating saw, starting at the right border of the second and fifth intercostal spaces and extending to the midline, followed by connection of both incisions (Fig. 24.3C) [39]. The distal end of the incision can be also extended to the base of the xiphoid process [40]. The advantage of this partial sternotomy is leaving the whole sternum intact and the right internal

FIGURE 24.3  Partial sternotomies through midline skin incision. (A) Upper J-shaped (dashed line). (B) Lower reverse J-shaped (dotted line). (C) Reverse C-shaped.

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mammary artery undisturbed. The first intercostal space can be selected when a complete exposure of the ascending aorta is needed. The ascending aorta, the aortic root, and the tip of the right atrial appendage can be clearly exposed through this incision.

Mini Thoracotomy Techniques Right Anterior (Parasternal) Thoracotomy This technique is the highly preferred procedure for minimal invasive AVR (Fig. 24.4A) [41]. All preparative steps are similar as in the standard operation, with the patient positioned supine, but the right chest can be elevated 30 degrees. Defibrillator pads are properly placed across the chest wall. The patient is intubated with a double-lumen endotracheal tube for single lung ventilation. The skin incision is performed in the third right intercostal space 2 cm away from the sternal edge without any rib resection, and the right lung is gently pushed down after opening the pleural cavity. After the pericardium is opened anterolaterally, the distal ascending aorta is cannulated in a standard fashion, frequently with a percutan arterial cannula. Venous cannulation or both cannulations are performed through femoral vessels to obtain more free space in the operative field. This approach is preferred mostly for sutureless AVR in selected patients because of limited exposure of the aortic root. The other disadvantage of this approach is costochondral disarticulation or rib fractures. Right Anterolateral Thoracotomy This technique can achieve an excellent cosmetic result for women (Fig. 24.4B) [42]. A 5–6 cm submammary skin incision is performed in the right midaxillary line, followed by both pectoralis major and minor muscles dissected free up to the fourth intercostal space. After the intercostal muscle is divided just to the upper edge of the fifth rib, the right pleura is opened. Single lung ventilation is started and the pericardium is opened. The exposure of the right atrium with both vena cava and ascending aorta is sufficient for cannulation and aortic valve surgery. Right Infra-axillary Thoracotomy This technique may limit the effective view and manipulation of the aortic valve due to the greater distance from the thoracic access site, and the smaller operative field leads to an added difficulty of requiring the use of long-shaft instruments (Fig. 24.4C). All cannulations are performed through peripheral vessels. After a partial left lateral position with the right arm flexed to 90 degrees, a 5-cm vertical skin incision is performed at the right anterior or midaxillary line and the pleura is opened at the third intercostal space [43]. The surgical procedure is performed using special endoscopic equipments.

FIGURE 24.4  Minithoracotomies through intercostal spaces. (A) Right anterior thoracotomy. (B) Right anterolateral thoracotomy. (C) Right infraaxillary thoracotomy.

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Endoscopic Interventions Video-Assisted This approach represents the first application of fully endoscopic AVR through the right anterior thoracotomy [44]. Using video equipment decreases incisions and prevents the removal of ribs or costochondral disarticulation. Cannulations must be performed peripherally. In fact, this approach has no added advantages over the minimal invasive AVR through the right anterior thoracotomy, and despite its attractiveness this approach has a learning curve and increases procedural cost. Totally Endoscopic Aortic Valve Replacement The less invasive approach could be the awake totally endoscopic AVR (TEAVR), but TEAVR is currently only performed under general anesthesia [45]. This approach could be feasible after the development of sutureless aortic valves, and as an alternative to TAVI [46]. Suitable ascending aorta must be nonvertical and longer (≥5 cm) with effective working distance between aorta and sternum (≥2.5 cm). All cannulations and cross-clamping are performed through the peripheral vessels. In fact, there are still a few surgical steps requiring long operative times such as decalcification or aortotomy closure through the small anterior thoracotomy incision, which prolong the total operative times. Robotic-Assisted This approach is very complicated and needs a special operating room with experienced surgeons [47]. All cannulations are performed peripherally, followed by a small (4–5 cm) anterior thoracotomy incision made just above the ascending aorta and two or three ports are placed. A robotic system with associated minimal invasive equipment is used to complete the rest of the operation in the usual fashion. In fact, there are still a few surgical steps requiring long operative times such as decalcification or aortotomy closure through small trocars, which prolong the total operative times [48].

Cardiopulmonary Bypass/Myocardial Protection Conventional aortic valve surgery can be performed under the standard extracorporeal circulation, and arterial and single venous cannulae should be inserted centrally to establish cardiopulmonary bypass. Cannulation during minimal invasive procedures is dependent upon the surgical approach. There are two steps necessary for standard sternal or every minimal approach: negative vacuum assisted cardiopulmonary bypass and carbon dioxide gas insufflation. Arterial cannulation should be performed as distal on the ascending aorta as possible in the course of standard sternotomy. However, the aortic arch may be more suitable for arterial cannulation in the course of mini-sternotomies, reoperations, aortic root or ascending aorta replacements, and calcified proximal aorta, as well as in the standard cases. Several minimal invasive approaches have a limited operative field, which cannot allow vessel cannulation and surgical intervention simultaneously. In these situations, any peripheral arterial cannulation is indispensable, but the right axillary artery cannulation is the preferred alternative. A standard arterial cannula can be used during conventional surgery, but a small, thinwalled, wire-reinforced, and flexible arterial cannula is more suitable during minimal approaches. The usual double purse strings without pledget are placed to fasten the cannula, and the cannula is inserted through them using a needle-guidewire technique (Seldinger technique), which allows for safe and controlled cannulation. A single dual-stage venous cannula is inserted through the right atrial appendage. Vacuum-assisted venous drainage (negative pressure approximately −50 to −80 mmHg) allows the use of a smaller size two-stage venous cannula to avoid mechanical complications of a bigger venous cannula and to decompress the heart with or without a left atrial vent insertion through the right superior pulmonary vein. A small dual-stage venous cannula is the best option during minimal invasive surgery but venous drainage may also be accomplished peripherally via the right femoral vein (and/or the right jugular vein) using with a thin-walled, wire-reinforced cannula with multiple holes using a percutaneous needle guidewire technique. After cardiopulmonary bypass is started, the ascending aorta is clamped and the heart is arrested using antegrade isothermic blood cardioplegia administered into the aortic root. After aortotomy incision, myocardial protection is maintained with intermittent antegrade isothermic blood cardioplegia into the coronary ostia using a selective coronary ostial cannula. Myocardial protection can also be maintained through continuous retrograde cardioplegia throughout the procedure, as long as clear visualization of the aortic root is not required [49]. The last option is the placement of the retrograde cannula into the coronary sinus under direct visualization after bicaval cannulation. A vent cannula is placed in the left atrium through the right upper pulmonary vein to allow drainage the left ventricle. Continuous insufflation of carbon dioxide is used to fill the left ventricular cavity for prevention of possible air embolization.

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TABLE 24.2  Aortotomy Incisions 1. Transverse aortotomy 2. Total aortic transection 3. Oblique S-shaped aortotomy 4. Oblique longitudinal aortotomy 5. Reverse-U-aortotomy

Aortotomy There are several classic approaches to open the ascending aorta for aortic valve resection and prosthesis implantation (Table 24.2). Each aortotomy technique has its advantages and disadvantages and the appropriate preferred approach is dependent upon several aortic factors: whether it is a primary or reoperation, the aorta is with or without coronary conduits, the aorta is thin or thick walled, is healthy or with severe calcifications, is small or large, as well as the prosthesis type and risk of PPM. Only a newly proposed aortotomy incision technique (Kırali incision) maintains all the advantages of the other approaches combined, while minimizing the disadvantages. All aortotomy incisions begin with the same small initial transverse aortotomy incision (1.5–2 cm long), which is initially made at least 15 mm above the origin of the right coronary artery (RCA) or the sinotubular junction (STJ). Through this small incision, the aortic valve is investigated under direct visualization, which allows the decision for which aortotomy approach is optimal and preferred.

Transverse Aortotomy This incision is the most common approach for isolated conventional AVR (Fig. 24.5A). The initial transverse aortotomy incision is extended on both sides until a three-dimensional view of the aortic root appears, but care must be taken to leave approximately one-third of the posterior end of the ascending aorta intact. The transverse aortotomy must remain clear of the tops of the commissures, and also from the RCA. If the RCA is superiorly located, this approach can be harmful due to ecartation of the proximal aortotomy edge, and therefore must be avoided.

Total Aortotomy This incision is not often preferred over conventional AVR, but it can be a valuable option in special circumstances. This approach is used mostly for AVR with allograft, pulmonary autograft, or stentless bioprosthesis requiring replacement of the complete aortic root. However, when this approach is used for reoperation, closing the aortotomy may not be possible and a graft interposition may be needed. The initial transverse aortotomy is extended on both sides and the ascending aorta is completely divided 2 cm above the STJ.

Oblique S-shape Aortotomy This incision is usually preferred for the conventional AVR with a small aortic root or normal aortic root with annular dilatation (Fig. 24.5B). An oblique S-shape incision is started from the initial transverse aortotomy incision. The lateral edge of the initial incision is extended arcuately upward a few centimeters, and the medial edge is extended arcuately downward into the middle of the noncoronary sinus (NCS) and stopped according to the aortic valve pathology. If the standard AVR is performed, the incision is stopped at the STJ or 10 mm above the aortic annulus. If an aortic annular enlargement is necessary, the incision is extended until the ventriculo-arterial junction or the mitral valve.

Oblique Longitudinal Aortotomy The oblique or hockey stick incision is used very seldom. This approach is sometimes preferred during thoracotomic AVR. The aortotomy is started on the medial aspect of the aorta and continued diagonally or longitudinally downward into the NCS.

Reverse-U-aortotomy (Kırali Incision) This new type incision is offered as a very useful approach in all kinds of primary valvular, subvalvular, and supravalvular aortic operations due to its predominant advantages (Table 24.3) [50]. Reoperations for AVR are a specific

FIGURE 24.5  Aortotomies. (A) Transverse aortotomy (completed incision is total aortotomy). (B) Oblique S-shaped aortotomy. (C) Reverse-U-aortotomy.

TABLE 24.3  Reverse-U-aortotomy (Kırali Incision) 1. Indications a. Standard conventional AVR with all prosthetic types b. AVR with hemisternotomy techniques c. AVR after previous coronary artery bypass grafting with proximal anastomoses (no-touch technique) d. Superior located right coronary artery e. Severe calcification(s) on the way of standard aortotomy approaches f. AVR with patient–prosthesis mismatch risk (small aortic root with appropriately sized aortic annulus) g. Aortic root enlargement i. posterior ii. anterior iii. combined h. Second open-heart surgery for AVR i. Supravalvular stenosis j. Subaortic pathologies (IHSS, SDM) 2. Advantages a. to adjust suitable distance from aortic valve and root (close or far according to prosthesis type) b. to provide the most excellent exposure of the aortic valve, c. to minimize dissection on the ascending aorta for aortotomy d. to eliminate unnecessary dissection for severe adhesion of cardiac structure e. to protect the whole posterior half of the ascending aorta intact f. to avoid stretching and tension on the rest of the intact ascending aorta g. to close aortotomy tension- and risk-free h. to leave previous bypass conduits untouched i. to supply antegrade selective cardioplegia easier through proximal anastomoses j. to insert an appropriately sized stented aortic valve k. to perform aortic annular enlargement l. to allow sinus enlargement when aortotomy cannot be closed AVR, aortic valve replacement; IHSS, idiopathic hypertrophic subaortic stenosis; SDM, subaortic discrete membrane.

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indication for this approach [51,52]. The initial transverse aortotomy is performed according to the surgery. If the AVR is the first operation, the initial incision is made at least 2 cm above the STJ. If an AVR is performed after previous CABG, the initial incision is made above or below proximal anastomoses leaving a minimum 2 cm distance from the STJ (3 cm above the RCA). The incision is continued down at both sides to complete the incision such as a reverse U-shape (as a tongue) (Fig. 24.5C). The medial edge of the initial incision is directed to the NCS, and the lateral edge is targeted directly to the commissure between the left and right coronary sinuses, but terminating both ends above the STJ. The tongue is retracted anteriorly with a 5/0 suture to exposure the aortic valve. This incision access in the aortic root is very trouble free and straightforward because both distal ends of the incision are opposite to each other, which means that the cardiac surgeon can access through the full diameter of the aorta just above the aortic valve, which is the most important advantage of this approach over the other approaches when determining the appropriately sized stented prosthesis (especially for low-profile bileaflet mechanical prostheses) to prevent PPM. If an annular enlargement procedure is necessary, the medial incision is extended to the annulus or mitral valve for posterior annular enlargement.

Valve Resection Aortic valve stenosis occurs with fusion of one or both commissures, thickening, and retraction of the cusps with and without calcification, and restriction of the aortic orifice. The calcification at the leaflets often extends to the annulus and surrounding tissues. The most severe form is characterized by diffuse calcification of the aortic annulus and root (porcelain aorta). A surgically complete decalcification of the aortic annulus is the key step in the surgical AVR (Table 24.4) [24]. Unless the aortic valve is noncalcific, aortic leaflets are cut by a scissor leaving a 3–4 mm margin at the annulus to hold replacement sutures securely. If the aortic valve is heavily calcified with healthy annular margins of the leaflets, the calcific aortic valve is excised and trimmed with a scissor leaving a 2–3 mm margin at the annulus. A frequent scenario involves the extensive calcification of the whole aortic annulus. Excision of the calcified leaflets with a scissor is usually unsuccessful and dangerous because of possible breaking of calcifications resulting in falling calcium debris into the left ventricle. The best approach to remove the diseased tissue is excision all leaflets with a lancet (number 15). A folded segment of sponge or tampon is not necessary to place in the left ventricle and it hinders the visualization of the cavity and removal of calcium particles. The easiest excision approach using the lancet is to perforate the healthy leaflet near the annulus in a partially calcified aortic valve or to begin excision at the commissure between the noncoronary and right coronary leaflets in an en-bloc calcified aortic valve. Cutting of the calcification is begun at the nearest end and the lancet incises the calcified valve from the healthy annular tissue. The sharp edge of the lancet should be headed toward the calcified valve, and cutting is performed just below the calcification. The whole calcified valve must be excised en-block without fragmentation. If calcification is very heavy or invades into the annulus it can be cut with the scissor and then the residual calcifications can be gently crushed and removed with a rongeur. After completion of the aortic valve excision, all residual diseased and/ or calcified tissue or particles should be removed from around the annulus, for example, by a small curette. Before sizing the prosthesis, the left ventricular cavity is flushed and irrigated with saline solution. During this step, if the calcification has spread to the aortomitral curtain and anterior mitral leaflet it can be also removed simultaneously to mobilize anterior leaflet. The weakened area on the aortic annulus requires repair to prevent perforation, detachment, or postsuturing tears. If the continuity is not fully disrupted, the weakened area must be secured between Teflon pledgets of anchor-sutures and the sewing ring of the prosthesis. If any detachment occurs, a limited defect should be approximated with a 5/0 polypropylene suture or a larger defect should be supported with pledgeted sutures.

TABLE 24.4  Decalcification Strategies of Aortic Annulus 1. not to leave any calcific tissue around the aortic annulus, 2. not to allow fragments of calcium to fall into the left ventricle, 3. not to disrupt the annulus if possible, 4. not to detach the anterior mitral leaflet from the annulus (noncoronary sinus), 5. not to rupture subannular muscular septum (right coronary sinus), 6. not to perforate outside the heart (left coronary sinus).

268  PART | III Treatment

Selection of Prosthesis-type A bileaflet mechanical prosthesis is the gold standard for conventional AVR in patients younger than 60 years, but also in any age group. The advantages are easy implantation techniques, long-term durability, better freedom from valve-related adverse events and re-replacement, and safe use patients with in chronic diseases (i.e., renal failure, hypercholesterolemia, hypercoagulable state, etc.). The disadvantages are a risk of PPM, lifelong anticoagulation, hemorrhage, risk of thrombosis or stuck valve, and disturbing sounds. Because mechanical prostheses have a smaller effective orifice area than the measured geometric orifice area, newly designed valves with thinner sewing rings and larger inner diameters may solve PPM related-problems in patients with a small aortic annulus. Supra-annular position, oblique implantation, supra-annular enlargement, or securing all sutures at the NCS outside can be chosen to ensure the use of the appropriate size and prevent PPM. One of the more attractive approaches is a posterior annular enlargement using a patch [53]. In the real world, a significant percent (approximately 40%) of the cases has small aortic annulus and 19 or 21 mm valves are usually implanted to avoid an annular enlargement [54]. Biologic aortic prostheses are the first option considered in the older population to avoid anticoagulation-related complications. Stented bioprostheses are the most commonly used valves due to ease of implantation, similar to stented mechanical valves. Stentless valves without obstructive stent and strut posts are useful to prevent PPM, but also the newer generation of stented bioprostheses has a larger effective orifice area. The best advantage of stentless bioprostheses is to give an opportunity for TAVI after the stentless bioprosthesis degenerates and requires a reintervention. The advantages include no need or contraindication for warfarin therapy, use in chronic hepatic disease, and improved long-term durability. Noiseless function is usually the main reason for patients to prefer a bioprosthesis [55]. The main disadvantage is a structural degeneration, which requires a second operation. Sutureless bioprostheses are the best option for high-risk patients and/or all types of minimal invasive AVR. They can be implanted more easily (without suturing, smooth anchoring) and faster (cross-clamp time <15 min for implantation after aortic valve resection) than the others, where cross-clamp time is reduced > 40% compared to procedures for implanting stented bioprostheses. Advantages include avoidance of full median sternotomy, shorter ischemic time, and avoidance of placing and knotting sutures; however, the sutureless bioprostheses have the disadvantage of containing long equipments or paravalvular leakage.

Position of Prostheses Position of a stented aortic prosthetic valve is very important to prevent a PPM, aortic tear, or unclosure of aortotomy incision, which requires patch closure of aortotomy incision, aortic annular enlargement, or aortic root replacement (Table 24.5). The less invasive solution is the oblique position of the stented prosthesis with external sutures on the NCS. The preferred approach is the intra-annular anchorage of stented prosthesis with an appropriately prosthetic effective orifice area. The best option for small aortic annulus is to prefer a stentless or sutureless bioprosthesis.

Techniques for Suture Insertion Suturing of a prosthetic aortic valve is the key step of the AVR. All stitches should be placed deeply enough to strengthen and secure the implantation. There are several approaches with their pros and cons (Fig. 24.6).

Stented Valves The most commonly preferred suture technique for stented prostheses is interrupted suturing approach using 2/0 sutures (Fig. 24.7A); however, continuous suturing is usually not preferred (Fig. 24.7B). A total of approximately 18 single deeply biting TABLE 24.5  Anchorage Techniques for Stented Prosthesis to Prevent a Patient–Prosthesis Mismatch 1. Prosthesis with a thinned sewing ring 2. Supra-annular position 3. Oblique position 4. External sutures on the noncoronary sinus 5. Stentless or sutureless valves 6. Patch closure of aortotomy 7. Aortic annular enlargement 8. Aortic root replacement

Conventional Aortic Valve Surgery (Open Surgical Approaches) Chapter | 24  269

FIGURE 24.6  Suturing techniques. (A) Interrupted suturing. (B) Continuous suturing. (C) 8-shaped suturing. (D) Subannular pledgeted suturing. (E) Supra-annular pledgeted suturing.

FIGURE 24.7  Suturing techniques without pledgeted support. (A) Single interrupted suturing. (B) Continuous suturing.

sutures along the annulus can be used to get a satisfactory anchorage of the stent either into or onto the aortic annulus. When the aortic annulus is destroyed or too friable for anchorage, the related (or all) sutures should be supported with pledgets. There are two methods for placing pledgets at the annulus: supra-annular position of pledgets is performed in an everted manner to put the stent into annulus (Fig. 24.8A); subannular position of pledgets is more reliable due to buttressing effect, where the sewing ring and pledget compress the weakened annulus from both sides as a sandwich (Fig. 24.8B). Subannular insertion of pledgets has several advantages such as to facilitate supraannular valve implantation, to support annular defects, to repair aortomitral discontinuity, and to purse up the thinned sinusal aortic wall on itself for the prevention of late aneurysmal growth.

Stentless Valves The single suture line technique is a simple, quick, safe, and reliable method to replace the native aortic valve with a stentless valve [24]. In this approach, the device should fit the supra-annular area because the trimmed aortic wall of the stentless valves is sutured and attached only with a proximal supra-annular suture line directly to native aortic sinuses in a supraannular position. Three 4/0 polypropylene sutures are started at the nadir of each sinus and brought progressively up to each commissural tip with the ends brought outside the aorta for tying. Running sutures avoid any prosthetic dead space between prosthetic valve and native aortic wall. This approach is used for implantation of the new generation scalloped tissue valves in the supra-annular position. Because the stentless valve will be placed supra-annular, the selection of a prosthesis one size larger than the native annulus minimizes the stress on the suture lines.

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FIGURE 24.8  Suturing techniques with pledgeted support. (A) Supra-annular position. (B) Subannular position.

FIGURE 24.9  Sutureless technique.

Sutureless Valves Without sutures, the implantation of an aortic prosthesis has been the goal procedure (Fig. 24.9). The new architectural design of sutureless bioprostheses allows perfect function after it adapts itself to the aortic root. Avoidance of suture lines makes the procedure easier, and only transient guide-suture(s) may be required to ensure the correct positioning and orientation of the prosthesis. A sutureless valve is stabilized in the aortic root with its root-like shape after anchorage to the aortic root in the Valsalva sinuses or below the annulus with a cylindrical ring segment after it reaches a final diameter compatible with the aortic annulus.

OUTCOMES Operative Mortality and Survival Operative mortality rate has been decreasing in the last 50 years and has reached a plateau in the last decade. Operative mortality changes for every age decade, sex, concomitant systemic diseases, previous valve surgery, and presence of

Conventional Aortic Valve Surgery (Open Surgical Approaches) Chapter | 24  271

heart failure (Table 24.6) [56]. On the other hand, the Society of Thoracic Surgeon (STS) database has shown continual improvement in operative mortality of AVR with concomitant CABG from 6.3% in 2001 to 4.4% in 2010 [57]. The type of aortic prosthesis (mechanical or biological) has no impact on operative mortality. Most operative deaths are related to several risk factors, including older age, functional status, neurologic complications, renal dysfunction, pulmonary dysfunction, and infection. Long-term survival has improved due to improvements in hemodynamically designed prostheses, which decrease transvalvular gradient and prevent late degeneration. Preoperative aortic pathology can affect long-term prognosis, and each TABLE 24.6  Operative Mortality Rates for Isolated Aortic Valve Replacement 1997

2006

3.4%

2.6%

Elective

2.8%

1.9%

Urgent

6.5%

4.9%

Women

4.1%

3.2%

Men

2.8%

2.1%

≤70 years

2.2%

1.3%

>70 years

4.6%

3.7%

No

3.3%

2.4%

Yes

4.8%

5.6%

No

2.1%

1.6%

Yes

5.2%

4.4%

No

3.2%

2.4%

Yes

6%

5.2%

No

2.9%

2.2%

Yes

13.9%

8.5%

<55

1.5%

0.9%

55–59

2.2%

0.6%

60–64

3.2%

1.6%

65–69

2.6%

1.9%

70–74

3.2%

2.9%

75–79

4.6%

3.3%

80–84

6.3%

4.9%

85–89

7.8%

4.1%

≥90

3.6%

9.6%

All Timing

Sex

Age

Previous valve surgery

Congestive heart failure

Ejection fraction <30%

Renal failure

Age groups

272  PART | III Treatment

survival data should be evaluated separately. Long-term survival rates for the heterogenous population are approximately >95%, 75%, 60%, and 40% at 1, 5, 10, and 15 years, respectively. The longer survival rates have been published: 32%, 22%, and 14% at 20, 25, and 30 years, respectively. However, 30-year freedom from valve related mortality is very successful (≈75%) [54]. Long-term survival rates are slightly lower in the heterogenous population older than 70 years: >90%, >75%, >45%, >40%, and >30% at 1, 5, 10, 15, and 20 years [58]. Pure severe AS treated with AVR (with or without concomitant CABG) has acceptable long-term survival rates but they decrease in older patients (≥70 years): 88.6%, 71.6%, and 31.8% at 1, 5, and 10 years, respectively [59]. Predictors of longterm mortality are nonelective intervention, LVEF ≤ 40%, worse functional status, and older age. Every decade after 70 years can impair approximate 1-, 5-, and 10-year survival rates: septuagenarians >90%, >75%, >45% [58]; octogenarians >90%, >75%, and 21.7% [60,61]; and nonagenarians > 80% (and 46.2% at 2 years) [62]. On the other hand, patients with standard severe AS have a better prognosis than those with paradoxical severe AS with or without low LVEF [63]. True-severe AS with LVEF < 40% in younger population (mean age 55 years) benefits from AVR and for that reason they should undergo surgery in the earliest phase of left ventricular dysfunction to improve the long-term survival (83% and 60% at 5 and 10 years, respectively), whereas preoperative worsening of left ventricular dysfunction affects the long-term survival [64]. Chronic severe AR treated with AVR (with or without concomitant ascending aorta replacement) has similar long-term survival to an age- and sex-matched population: 96%, 90%, and 77% at 1, 5, and 10 years, respectively [56]. The main difference between subgroups relates to left ventricular dimension indices [cut points for indexed LVESD 2.5 cm/m2 (P < .001) and indexed LVEDD 3 cm/m2 (P = .002)], but not depressed LVEF or increased left ventricular dimensions.

Stroke There are many factors that can cause a transient or permanent neurologic deficits: particle or air embolizations, cerebrovascular disease, and low perfusion flow. Despite the decrease in stroke rate following isolated AVR to 1.3% patients with older age (>75 years), renal failure or peripheral vascular diseases still have a 50% greater stroke risk than patients without those predictors.

Complete Heart Block Sinus node dysfunction, bundle branch blocks, or complete heart block may revert back to normal sinus rhythm during the early postoperative period and also require temporary pacing. The requirement of a permanent pacemaker after AVR is a rare (4.1%) but serious complication [65]. Debridement of a severely calcified aortic annulus and/or placement of deeper sutures may damage the conduction system, especially in the bundle of His. Annular calcification, bicuspid aorta, female sex, and presence of preoperative conduction defects increase this risk.

Postoperative Complications The most common early postoperative complications include atrial fibrillation (37.8%), prolonged (>1 day) ventilation (15.3%), low cardiac output (6.5%), and reexploration for bleeding (5.2%) [59]. Some late complications related to the prosthesis (i.e., paravalvular leakage, prosthetic valve endocarditis, pannus formation, etc.) develop very rarely due to the improvement of surgical techniques, new antibiotics, and new design of prostheses. Postoperative events related to warfarin therapy are still the most significant complications that can cause death or severe neurologic deficits. Thirty-year freedom from reoperation or endocarditis is very high (92%), but freedom from thromboembolism is acceptable (76%; 1.6%/patientyear); however, freedom from bleeding is serious (56%; 2.5%/patient-year) [54].

Anticoagulant-Related Late Complications The most important complications during follow-up are related to chronic warfarin therapy: excessive anticoagulation may cause severe hemorrhage in different organs, especially gastrointestinal or intracranial bleeding; too little anticoagulation may result in thromboembolic events, including valve thrombosis. Mechanical prostheses with continuous warfarin therapy are most at risk. Bileaflet mechanical valves in the aortic position need less anticoagulation than those in the mitral position, and the valve thrombosis risk is also very low. Excessive warfarin may still lead to fatal bleeding during follow-up, and the international normalized ratio for management of warfarin dosage should be held between 2 and 3 for mechanical aortic prostheses. Anticoagulant therapy is discontinued in bioprostheses after the third postoperative month, which decreases the risk of anticoagulant-related late complications.

Conventional Aortic Valve Surgery (Open Surgical Approaches) Chapter | 24  273

Structural Valve Degeneration Primary tissue failure is the most important valve-related complication during follow-up. Structural valve degeneration (SVD) means any abnormality in prosthetic function resulting from an intrinsic degeneration (i.e., stenosis, leaflet tears, suture line disruption, calcification, etc.). The overall incidence of SVD is about 5% at 10 years, which is affected mostly by age. Age <60 increases early SVD threefold compared with older age, which can require a re-replacement, whereas age >70 is associated with a higher rate of freedom from SVD and related reoperation [66,67]. Midterm results of stentless and sutureless bioprostheses are better than stented bioprostheses, especially in small valves [10,68]. Despite the lack of data on long-term durability, stentless or sutureless bioprostheses seem to be the preferred option of a biologic aortic prosthesis in patients aged <60 years because the valve-in-valve procedure may be the most suitable and noninvasive treatment solution against a surgical reoperation.

FUTURE Surgical AVR using the conventional approach (general anesthesia + full median sternotomy + stented valve implantation) is still the gold standard, whereas minimally invasive approaches are often suitable and appropriate alternatives. ReverseU-shaped aortotomy is the best option to perform all kinds of operations for supra-annular, annular, and subannular aortic pathologies. Every cardiac surgeon should appreciate the step-by-step learning curve of AVR: first conventional surgery with stented valves, then stentless valves, then sutureless valves, and then minimal invasive approaches. There is currently no place for transfemoral or transapical aortic valve implantations in patients due to significant risks. Clear guidelines are available for treatment modalities in patients with isolated aortic valve diseases, but patient profile is the first determinant in selecting the optimal intervention. The future will be built on the surgical approaches, implantation techniques, development of new prostheses, and more practical use of robotic systems. It seems that the optimum strategy for aortic valve intervention may advance to a computerized surgery in future. Younger patients might benefit from bioprostheses as a result of future improvements in prevention of structural degeneration, the valve-in-valve approach, and the shapable structure of bioprostheses for minimal invasive surgery.

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