Chapter 35. Aortic Valve Replacement with a Stentless Bioprosthetic Valve: Porcine or Pericardial

The history of stentless xenograft aortic valves follows in the footsteps of the aortic homograft, which was considered historically as the best biologic prosthesis for management of root pathology and for optimizing hemodynamics in the absence of root pathology. The original concept behind creating a stentless xenograft valve was to maintain the excellent hemodynamics of the homograft, while improving on the availability, durability, technical complexity, and costs associated with homografts.

Stentless, or "natural valve" substitutes closely mimic the native aortic root anatomy and are implanted without a stent, large sewing ring, or other supporting apparatus that can lead to persistent LV obstruction sometimes observed with stented bioprostheses or mechanical valves. In general, use of stentless valves also allows for implantation of larger prostheses with resultant larger effective orifice area for any given LV outflow tract diameter. Comparing homografts, autografts and xenografts, stentless porcine constructs have the most opportunity for wide-spread application because of their ready shelf availability and ease of implantation. Compared with traditional stented bioprostheses, touted advantages of stentless valves include better hemodynamics,1-3 improved regression of left ventricular mass,3-5 less risk of patient-prosthesis mismatch (ppm) in the small aortic root,6 and possibly improved long-term survival.7,8 Because of these advantages, over the past 15 years, aortic valve replacement (AVR) with stentless porcine bioprostheses has become an accepted technique for routine treatment of aortic valve and root diseases. Some of these advantages appear to be maximized with implantation using a total root replacement technique, which also is associated with less risk of late valve failure.9 However, the potential benefits of stentless valves implanted as total roots may come at the cost of increased operative risks, including a potential for higher operative mortality compared with subcoronary stentless or stented AVR.9 Although other large series have reported low operative mortality with stentless root replacement,10-12 a learning curve of over 20 cases has been described.13 Besides a learning curve for this more complex procedure, other factors that could potentially contribute to excess mortality include longer perfusion and myocardial ischemic times, and more suture lines exposed to the pericardial space. Thus, the use of stentless aortic bioprostheses has become a controversial topic within the cardiothoracic surgical community.

Many stentless xenograft valves have come and gone in the marketplace over the past decade. Currently, the only two stentless prostheses available are the Medtronic Freestyle bioprosthesis and the ATS 3F valve, which has only recently been introduced to the North American market.

Medtronic Freestyle

The Medtronic Freestyle valve followed closely behind the development of the St Jude Toronto SPV, which is now out of production. From its beginning, the Freestyle valve had several options of implantation techniques, similar to the homograft, including full root, root inclusion, and subcoronary positions. The Freestyle valve began clinical application in the early 1990s, thus making some long-term outcome data available. The Freestyle is a complete porcine root with minimal polyester fabric covering all exposed porcine myocardium (Figs. 35-1, 35-2). This serves to strengthen the proximal (inflow) suture line and reduce antigenicity. There is a green demarcation line around the inner circumference of the polyester fabric covering indicating the suturing area. There are also markers for each commissure to aid in suture placement. The Freestyle tissue is crosslinked in a dilute glutaraldehyde solution using a tissue fixation method that allows valves to maintain natural leaflet structure and natural root geometry by simultaneously applying 40 mm Hg (diastolic pressure of the pig) to the inflow and outflow portions of the bioprosthesis, allowing the leaflets to relax at net zero pressure differential with a pressurized root.14 This results in leaflets fixed under no load but in an anatomically distended root. Potential advantages of this process include maintenance of radial leaflet distensibility (corrugations), circumferential leaflet stability (crimp), maintenance of strength with elasticity, and mitigation of kinking. Using a combination of accelerated wear testing in a pulse duplicator and biaxial mechanical testing of the tissue, Christie and colleagues demonstrated better preservation of both circumferential and radial stretch in the Freestyle leaflets compared with leaflets fixed even at low pressure, which flattens the native collagen crimp.15 The Freestyle bioprosthesis is treated with an alpha-amino oleic acid (AOA), a compound derived from oleic acid, designed to mitigate both leaflet and wall calcification. Various anticalcification treatments are now commonly used by all manufacturers with data based on animal and some short-term human efficacy studies. Minimal long-term human data exists on the effectiveness of any of these proprietary anticalcification treatments, although the group at Harefield recently reported lower calcium scores in Freestyle valves compared with homografts at 8 years.16

ATS 3F Valve

The ATS Aortic Bioprosthesis, Model 1000 is a stentless pericardial aortic heart valve replacement designed as a tubular structure and constructed from three equal sections of equine pericardium, with each section cut roughly in the shape of a square (Fig. 35-3). This unique construction design was based on the development of the embryonic tubular aortic valve subjected to computer modeling. The choice of equine pericardium is reportedly based on its strength in the areas of the leaflets where stress was found to be greatest. For the 3F valve, this highest stress area is the midportion or "belly" of the leaflet. Equine pericardium is also reportedly thinner and more consistent in thickness compared with bovine pericardium. The equine pericardium is fixed with 0.25% buffered glutaraldehyde to preserve its collagen matrix and reduce its immunogenic and thrombogenic potentials while preserving its strength and flexibility. Anticalcification agents are not used. The proximal orifice of the valve has an attached thin polyester sewing ring used to attach the bioprosthesis to the aortic root orifice after resection of the diseased aortic valve. The distal portion of the valve has three commissural tabs, formed from contiguous sections of each of the leaflets and reinforcing polyester material that are used to attach the commissures to the native aortic wall. Similar to traditional subcoronary stentless valves, the 3F relies on normal root/annular ratios and geometry during implantation. The tubular design of the valve, however, allows the omission of the full subcoronary (outflow) suture line. Instead, the three commissures are attached to the aorta at 120-degree spacing at appropriate height from the annulus (Fig. 35-4).

Currently little data exist on the performance of the 3F valve, although at one year in a study of 35 implants, mean gradients ranged from 9 to13 mm Hg and there was minimal AI and no structural deterioration.17

Stentless aortic valves placed as a subcoronary or full root implant are indicated for the small aortic root, and root replacement provides better hemodynamic function than traditional root enlarging procedures. Stentless aortic valves placed as a total root are also useful in the following situations:

1. Aortic root disease when bioprosthesis is desired

2. Elderly patients with poor tissues. It is simpler to replace fragile disease tissues with synthetic material, thereby eliminating working with poor tissues and tension on critical suture lines.

3. Aortic dissection, when valve needs replacement. Extensive dissection in the sinuses of Valsalva is easily handled with a stentless root bioprosthesis.

4. Endocarditis. Similar to the homograft, the stentless root bioprosthesis allows maximal debridement prior to reconstruction, but has the advantage of immediate availability in all sizes.

Subcoronary and Modified Subcoronary

Function of the subcoronary stentless valve relies on the intact native sinus geometry. For this reason, an oblique aortotomy should not be used to approach the aortic valve, and instead, a transverse aortotomy or complete aortic transsection should be used. At least 1 to 1.5 cm of clearance is needed to place the stentless device within the root and still close it above the tips of the commissures of the new valve. Complete transsection of the aorta is often helpful in gaining full exposure for implantation. For traditional subcoronary technique, all three sinuses of the prosthesis are scalloped out. For modified subcoronary implantation, the noncoronary sinus is left intact. The advantages are higher suture line, and two posts are fixed. The proximal suture line is usually done with simple interrupted technique using 2-0 to 4-0 braided sutures. Approximately 20 to 30 sutures are used depending on the size of the annulus (Fig. 35-5). Suture guides are very helpful in keeping these many sutures organized. The device is parachuted down into the root and the sutures tied and cut. The right and left sinuses are scalloped out either before or after this step (Fig. 35-6). A distal suture line of continuous small (4-0) caliber polypropylene suture is then constructed coursing below the coronary ostia, taking care not to buckle the stentless tissue or distort the positions of the commissural posts. Stay sutures can be placed at the top of each commissure to help maintain orientation. One suture is begun at the bottom of the left and another at the bottom of the right sinus and run up to the top of each commissure (Fig. 35-7). The porcine tissue and especially the cloth-covered portion of some devices must not encroach on the ostium of either coronary, because obstructive granulation tissue may form in this location. The top of the device is trimmed down to the level of the native aorta, taking care to stay above the top of each commissure. If the noncoronary sinus of the stentless valve is kept intact, the distal suture line can be completed by running along the top to join the two sutures. The aortotomy is closed with continuous suture incorporating the tops of the commissures and the retained noncoronary sinus edge. The completed concept of the complete and modified subcoronary implant technique is shown in Figs. 35-8 and 35-9.

An expanding hematoma in the space between the native and the porcine noncoronary sinus walls is undesirable, but a small, fixed collection in this area usually resorbs over time. One technique to minimize this problem is to rotate the Freestyle root 120 degrees to put the porcine right coronary stump in the patient's noncoronary sinus. A small cut in the sinus allows the porcine stump to be extruded to the outside of the native sinus where it is secured with a pledgeted mattress suture of 4-0 polypropylene.

The subcoronary method has been preferred by most early adopters of the stentless valve because the first available, the Toronto SPV, was a completely scalloped device that required this method of implantation. In general, sizing and implantation of the subcoronary stentless valve is more prone to error compared with stented and full-root replacement operations. To assure valve competency, the recipient must have a normal ratio between annulus and ST junction diameter (<3 mm difference). Because relative dilatation of the ST junction can create valvular insufficiency, many surgeons choose a valve size based on this diameter, not the annular diameter. Sinus dilation can also cause insufficiency, but this would be unusual without concomitant ST junction effacement.

Oversizing of the stentless valve leads to higher transvalvular gradients. This is because of the compressible nature of the valve such that when placed in a fixed space such as the aortic root, excess tissue can lead to obstruction. Inflow buckling of the prosthesis may also lead to insufficiency and excessive turbulence. Undersizing leads to insufficiency by stretching of the prosthetic tissue with resultant loss of coaptation.

Root Inclusion

In an effort to completely preserve the three-dimensional geometry of the bioprosthetic root devices without completely replacing the native root, a minority of users have chosen to employ the root inclusion method. This involves a proximal suture line (continuous or interrupted) like the subcoronary technique in a circular plane coursing below the commissures. Generous openings are made by excising the sinuses facing the right and left main coronary ostia (Fig. 35-10). These are then tacked around the ostia much as a root inclusion Bentall procedure with continuous 4-0 polypropylene suture. The aortotomy is then closed in standard fashion after trimming the device top down as necessary to incorporate in the closure, making sure that the complete circle of the sinotubular junction is left intact. The only difference between the root inclusion method and the subcoronary technique is that the complete sinotubular ring of the stentless device is preserved, thus preventing any chance of dilatation at that level in the future. The top of the device is incorporated in the closure of the aortotomy (Fig.35-11). Practically, this method is the most difficult and should not be used unless the root is large enough to place a 23-mm or larger device. It may, however, be the most desirable in a younger patient with a larger aortic root. The bioprosthetic sinotubular junction will not dilate over time, and at a subsequent operation, after gently removing this device, the entire native aortic root will be available for a complete range of replacement choices.

Full Root Replacement

Total replacement of the aortic root in most respects is the easiest and most reliable technique for stentless aortic valve replacement. Exposure of the annulus, calcified leaflets, and LV outflow tract is enhanced when the root is removed and the coronary ostia are mobilized out of the way. Decalcification of the annulus and aortomitral curtain becomes straightforward. Each suture is simple to place, making malalignment and poor bites of tissue less likely. Treatment of ascending aorta pathology with a Dacron tube graft extension becomes easy and logical. Perhaps most importantly, optimal hemodynamics are obtained.

The procedure begins with transection of the aorta just above the sinotubular junction (Fig. 35-12). Both coronary ostia are mobilized on generous buttons of aortic wall (Fig. 35-13). The remaining tissue of each sinus of Valsalva and the diseased aortic valve are excised. The valve is sized by identifying the largest sizer that will pass into the left ventricular cavity, then choosing one size larger valve so that the internal orifice of the prosthesis will match the left ventricular outflow tract diameter (Fig. 35-14). The proximal or inflow anastomosis is accomplished using 28 to 35 simple interrupted sutures of 3-0 braided Dacron tied around a 3-mm strip of Teflon felt (Fig. 35-15). The sutures are placed in a single plane in the left ventricular outflow tract to conform to the round inflow of the prosthesis. The coronary arteries on their buttons of aortic wall are sewn end- to-side to the corresponding sinus of Valsalva of the bioprosthesis with a continuous 5-0 polypropylene suture (Fig. 35-16). The distal end of the bioprosthesis is sewn end-to-end to the aorta with a continuous 5-0 polypropylene suture to complete the root replacement (Fig. 35-17).

Coronary Alignment

To correctly align the coronary buttons on the porcine full root prosthesis, the similarities and differences between human and porcine aortic root anatomy must be appreciated. The anatomy between the two roots is similar in that the left main arises from the middle of the left sinus of Valsalva with similar heights from the annulus in both human and pig. Also similar to both roots, the right coronary artery is situated slightly higher (more distal) above the annulus. The right coronary artery arises closer to the left coronary in the pig compared with the human. Specifically, porcine coronary arteries are oriented approximately 90 to 110 degrees apart compared with human coronaries, which normally lie 140 to 160 degrees apart, but up to 180 degrees apart in patients with truly bicuspid valves. Practically, this means that the porcine root will need to be rotated 120 degrees during implantation in most situations, so that the porcine noncoronary sinus will be used for reimplantation of either the right or left coronary artery. Flexibility is crucial during coronary alignment, given the inherent anatomic differences seen between patients and prostheses. Native orientation and height must be maintained to prevent coronary insufficiency, an unusual event that most commonly involves the right coronary artery.18 Signs of right coronary insufficiency include right ventricular dilatation, EKG changes, and otherwise unexplained arrhythmias. Frequently, these findings are only present upon ventricular filling, which may exacerbate a kinked or malaligned proximal right coronary artery. Saphenous vein grafting without repeat cross clamping should be liberally performed if there is any unexplained ventricular abnormality that prevents easy wean from cardiopulmonary bypass.

Calcified Coronary Buttons

Severe calcification of the sinuses of Valsalva is often cited as a contraindication to total root replacement. Typically, this calcification will not be isolated to the sinuses, and traditional stented or mechanical valves are often difficult to place as well, with higher risks of paravalvular leak, bleeding from anastomoses, and coronary dissection. With appropriate recognition and button management, severe root calcification is often best managed with total root replacement, which allows for the most effective removal of calcified and poor quality tissue. Tailoring button size to avoid suturing of calcified sinus tissue is one option to facilitate reimplantation, as is ligation and bypass grafting. Usually, endarterectomy of the coronary ostium must be performed to achieve a hemostatic ligation.

Pathology of the Ascending Aorta

Replacement of the ascending aorta and arch is a natural extension of full root replacement and is performed in up to 55% of patients in large series.10,19 This speaks to the frequency of atherosclerotic and aneurysmal changes of the ascending aorta in patients with aortic valve disease. Replacement of the ascending aorta with a prosthetic graft, even when performed with a brief period of hypothermic circulatory arrest, adds no additional morbidity or mortality.20

Bleeding

Increased risk of bleeding complications is often cited as a reason to avoid total root replacement. Bleeding can occur from any of the four suture lines, but is uncommon when adequate resection of calcified tissue is performed. We have found that placement of an interrupted proximal suture line as described along with careful inspection of the coronary button anastomoses has made bleeding complications less frequent than might be expected. Bleeding from the proximal suture line is usually not manifest until the left ventricle is ejecting, and usually requires reclamping of the aorta, especially early in a surgeon's experience. Coronary buttons may need to be removed to access proximal suture lines in these locations. Other potential areas of bleeding include the right ventricle underneath the right coronary button, and small venous or arterial branches on the adventitia of the mobilized left coronary artery or medial aspect of the main or right pulmonary artery.

Reoperation

Reoperation for a failed stentless bioprosthesis can be challenging. We believe that a full root replacement for the reoperation is preferable if the root or sinuses are extensively calcified. If the reoperation is performed early, ie, for a paravalvular leak with a subcoronary implant, a prosthesis can be inserted inside the previously placed valve after leaflet removal. However, most patients with degenerated calcified aortic root prostheses will be best served with redo total root replacement.

Technical Tips to Facilitate Redo Total Root Replacement

1. Preoperative cardiac CT scan. This tells you the location within the mediastinum of any previous coronary bypass grafts. Knowledge of how close vascular structures reside to the underside of the sternum simplifies the process of reopening the sternum. The presence or absence of coronary anomalies or atherosclerotic vascular disease also helps plan the operation.

2. After the heart and great vessels are freed up and the aorta is cross clamped to arrest the heart, the aorta is transected at the prior distal anastomosis. Next one begins to separate the aortic root from the pulmonary artery. If adherence of these structures is excessive, one can develop a safer plane within the adventitia of the degenerated porcine root.

3. The left main coronary button should be re-mobilized at this time. Preservation of the left main button facilitates the rest of the dissection. Then the right main button is mobilized.

4. Once the coronaries are freed up and out of the way, the rest of the root can be mobilized circumferentially down to the previous inflow suture line. Proper traction/countertraction simplifies this dissection.

5. At this point one can simply cut the rest of the old aortic root out at its junction with the left ventricular outflow tract out.

The surgical field is now ready for the new total root replacement.

Evaluating the short and long term outcomes of stentless valves in the literature is difficult for several reasons: many manufactured valves are no longer in clinical use; long-term data is scarce; there exists little randomized prospective data comparing stentless versus stented valves; studies generally mix various AVR indications together (patients with root pathology differ from those with a small annulus undergoing stentless valves for avoidance of patient-prosthesis mismatch); and most importantly, the majority of studies on stentless valves include both subcoronary and full root implants together in the "stentless" arm. This results in a heterogeneous population undergoing surgery for differing indications, by surgeons with bias towards one technique over another, and using techniques that can result in vastly different hemodynamic and potentially long-term results.

Hemodynamics

It has been well proven that stentless valves offer superior hemodynamic profiles compared with their stented counterparts. Kunadian et al performed a meta-analysis of randomized, prospective trials of stentless versus stented AVR and included 10 studies and 919 patients from European centers.21 They demonstrated an approximately 6-mm Hg lower peak gradient for the stentless group, but no survival advantage at 1 year. Importantly, the vast majority of the stentless valves were implanted by subcoronary technique. As a full root replacement, stentless valve hemodynamics compare favorably to homografts, with nonsignificant differences in mean gradients reported between the two prostheses.22 Freedom from aortic insufficiency and degenerative changes also favors the Freestyle root over the homograft.23 Compared with subcoronary implantation, stentless full root replacement achieves lower gradients, larger effective orifice area, and greater freedom from at least moderate aortic insufficiency after 10 years of follow up.9 Studies on the subcoronary implant technique have consistently shown a decrease in gradient and increase in EOA over time. Early and late gradients are both low for total root replacement and generally do not change over time. This discrepancy is most likely related to absorption of hematoma in the potential space between the porcine and native aortic walls, which occurs when performing a subcoronary implant.

Reverse Remodeling and Survival

Regardless of valve substitute, AVR in patients with severe, symptomatic AS consistently results in improvements in both structural and clinical outcome compared with medical treatment. However, long-term survival after AVR remains lower than age-matched populations, for known and unknown reasons.24-26 Known factors related to higher death rates include bleeding with anticoagulation required for mechanical valves, thrombotic complications, endocarditis, and structural valve degeneration. Additionally, in patients with advanced myocardial damage and fibrosis, AVR would not be expected to allow for complete reverse remodeling, and lower long-term survival in this condition is intuitive. Indeed, low preoperative ejection fraction is perhaps the strongest predictor of long-term outcome.27,28 In patients with less advanced structural disease, however, incomplete reverse remodeling of the pressure overload state is an unknown prognostic variable. Even seven years after AVR with stented or mechanical valves, increased muscle fiber diameter and percent interstitial fibrosis compared with normal is observed,29 possibly because of persistent prosthetic LV obstruction and residual gradient.

To overcome the problem of residual gradient after AVR, stentless valves have been proposed as ideal for allowing reverse remodeling to occur. Using LV mass as the predominant surrogate marker, multiple small randomized and nonrandomized studies have attempted to assess for differences in reverse remodeling after AVR with different valve substitutes. Although demonstrating conflicting results, regression of LV mass does appear to be associated with achieving valvular competence and a low transvalvular gradient, regardless of prosthetic choice, and with treatment of postoperative hypertension.30 The ASSERT trial31 is one of the few randomized studies comparing the effects of stented versus stentless AVR on LV mass. In this study performed in Europe, 190 patients with aortic annulus size ≤25 mm were randomized to receive a Medtronic stented Mosaic porcine prosthesis or Medtronic stentless Freestyle prosthesis, implanted using a subcoronary technique. After one year, both groups demonstrated similar reductions in LV mass despite significant differences in effective orifice areas and flow velocities in favor of the stentless valves. Operative and postoperative clinical outcomes were also similar. A significant weaknesses of the study, however, was the use of the subcoronary technique for implantation of the stentless valve, which leads to higher gradients, more aortic insufficiency, and higher rates of late valve failure compared with the total root technique.9,32 Additionally, one year follow-up may be an inadequate time to detect for differences in LV hypertrophy, because changes in LV geometry occur over many years after AVR.33,34 This concept is supported by a small, randomized study of stented versus stentless valves that found no difference in LV mass regression at 6 months but a significant difference in favor of the stentless valve at 32 months.35 The most recent large randomized study compared Edwards Lifesciences stented and nonstented subcoronary prostheses in 161 patients and again demonstrated similar reductions in LV mass at 1 year. However, in patients with LV ejection fraction less than 60%, subsequent improvement in ejection fraction was greater in the stentless group.36 Because of these conflicting data, some have questioned the overall clinical importance of LV mass regression after AVR. Despite the known adverse prognostic implication of LV hypertrophy in the population as a whole, and importance of regression with treatment of hypertension, it has not been conclusively determined that regression after AVR correlates with survival.37

Gender issues are important to the topic of remodeling in aortic stenosis. For example, left ventricular adaptation to severe aortic stenosis is gender specific, with less compensatory increase in LV mass and wall tension in females compared with males.38,39 Perhaps a better indicator of hypertrophy is the LV mass/volume ratio, a parameter that is increased in women with aortic stenosis compared with men.39,40 Consequently, women with aortic stenosis tend to have worse diastolic function and exercise capacity compared with men.41 Patient-prosthesis mismatch (PPM) is also more common in women and refers to implantation of a valve too small for a patient's size. Although PPM is generally defined as an in vivo effective orifice area indexed to body surface area (EOAI) of ≤ 0.75 to 0.85 cm2/m2,42 EOAI may be preferentially evaluated on a continuum, similar to native aortic valve stenosis. Depending on definition, PPM is present in 20 to 60% of patients after AVR.43-45 EOAI incorporates both size and functional considerations because postoperative gradients (ie, persistent LV pressure-overload state) are related to the area available for blood to leave the LV and to flow, or cardiac output in this instance, which correlates well with body size. Although controversial,46-48 the preponderance of data, all retrospective, suggests that the presence of PPM is associated with reduced mid- and long-term survival.45,49-54 Techniques to prevent PPM include annular enlargement procedures and implantation of stentless valves.

Durability

History teaches a good lesson in the story of the Toronto SPV stentless valve. Pioneered by David, this was the first prosthesis widely available for use. The Toronto SPV was designed to be implanted only by subcoronary technique. Numerous reports identified the hemodynamic advantages over stented valves, and remarkably, David reported improved survival over stented valves in midterm follow-up.55 At 9 years, durability and hemodynamics were found to be excellent, with 90% freedom from structural failure.56 At 12 years, however, freedom from structural valve degeneration was only 69%, and only 52% for patients under 65 years of age at time of implant.57 Freedom from moderate or severe aortic insufficiency was only 48% for the group as a whole. The mechanism for this finding was postulated to be dilatation of the sinotubular junction, and such a mechanism could theoretically affect late results of any subcoronary stentless valve. In a group of mostly subcoronary Freestyle implants, however, Bach et al reported 92% freedom from structural degeneration at 12 years with equivalent rates in patients less than 60 years of age at the time of implant.58 One possible explanation, although not proven, for the discrepancy between SPV and Freestyle longevity is that most Freestyles have been implanted with the modified subcoronary technique compared with complete subcoronary for the Toronto SPV. The preservation of two commissural posts may create more sinotubular junction stability over time. In general, though, the lessons to be learned from the SPV data are that all valves are not created equal, even when implanted in similar manners, and that long-term and ongoing follow up is required to assess for durability because all bioprosthetic valves will eventually fail.

Operative Risk

Contemporary series of patients implanted with stentless valves do not support a higher operative risk, even with total root replacement. It is clear that the procedure requires slightly longer aortic cross-clamp and CPB times,21 but this has not translated into higher mortality. Florath et al examined factors related to operative mortality in 1400 patients undergoing AVR, and neither stentless nor stented valve use was found to be predictive.12

As newer valve designs continue to be introduced to the market, ease and safety of implantation will continue to dominate as factors important for patients and surgeons. Closely followed in importance will be hemodynamic performance and durability. With the advent of transcatheter aortic valves, the bar will be set high for both implantation ease and hemodynamics. Already, effective orifice areas for first generation transcatheter valves exceeds those for 3rd generation stented bioprostheses,59 albeit at the expense of trace-to-moderate aortic regurgitation. This issue will continue to drive the debate over the importance of patient-prosthesis mismatch. In the coming years, these issues may also highlight the hemodynamic advantages of stentless valves over stented and may also define the importance of different valves as platforms for performing transcatheter valve-in-valve implantation. Stentless total roots may have an advantage over other aortic valve prostheses in this setting given the larger orifices and root anatomy that is equivalent to the anatomy used during transcatheter valve development.

In summary, the stentless aortic valve, when implanted as a total root replacement, is an undeniably important tool for management of aortic root pathology. The debate continues, however, over the use of stentless valves in the absence of root pathology. Given that survival and functional outcomes often remain impaired after AVR for aortic stenosis, and that this suboptimal outcome appears to coincide with incomplete reverse remodeling of the left ventricle, surgeons should continue to seek the best option for long-term quantity and quality of life. Placement of larger valve substitutes intuitively will result in lower residual transvalvular gradients and may allow for better myocardial structural and functional outcomes. Use of stentless valves optimally achieves these surgical goals and may be appropriate for broader applications.

• The indication for subcoronary or modified subcoronary stentless AVR is for prevention of patient-prosthesis mismatch and can be considered an alternative to annular enlargement procedures.
• Stentless valves placed as full roots maximize the hemodynamic advantages of stentless technology and can be placed without excess mortality.
• Stentless valves placed as full roots are an excellent alternative to homografts when a bioprosthesis is desired for treatment of aortic root pathology.
• Long-term data on currently available stentless valves reveals acceptable rates of structural degeneration.
• Tips for successful stentless root replacement include paying close attention to coronary alignment, interrupted proximal suture line, complete resection of calcified or poor quality tissue, and close inspection of coronary button suture lines.
• All stentless valves are not the same. Various techniques are utilized for implantation resulting in heterogeneous populations for different indications with different valves by surgeons with bias towards one technique over another. The result is vastly different hemodynamic profiles and long term outcomes.