Full-root aortic valve replacement by stentless aortic xenograft is a viable option in patients with small aortic roots. We describe, a technique for the full-root implantation of stentless aortic xenografts, with emphasis on the management of the proximal suture line and coronary anastomoses, and discuss its limitations and alternative options.
In patients with small aortic roots who need an aortic valve replacement with biological valve substitutes, the implantation of the stented pericardial valve might not meet the functional needs. The implantation of a too-small stented pericardial valve, leading to an effective orifice area indexed to a body surface area less than 0.85 cm2/m2, is regarded as prosthesis-patient mismatch (PPM). A PPM negatively affects the regression of left ventricular hypertrophy and thus the normalization of left ventricular function and the alleviation of symptoms. Persistent left ventricular hypertrophy is associated with an increased risk of arrhythmias and sudden cardiac death. In the case of predictable PPM, there are three options: 1) accept the PPM resulting from the implantation of a stented pericardial valve when comorbidities of the patient forbid the more technically demanding operative technique of implanting a larger prosthesis, 2) enlarge the aortic root to accommodate a larger stented valve substitute, or 3) implant a stentless biological valve or a homograft. Compared to classical aortic valve replacement with stented pericardial valves, the full-root implantation of stentless aortic xenografts offers the possibility of implanting a 3-4 mm larger valve in a given patient, thus allowing significant reduction in transvalvular gradients. However, a number of cardiac surgeons are reluctant to transform a classical aortic valve replacement with stented pericardial valves into the more technically challenging full-root implantation of stentless aortic xenografts. Given the potential hemodynamic advantages of stentless aortic xenografts, we have adopted full-root implantation to avoid PPM in patients with small aortic roots necessitating an aortic valve replacement. Here, we describe in detail a technique for the full-root implantation of stentless aortic xenografts, with emphasis on the management of the proximal suture line and coronary anastomoses. Limitations of this technique and alternative options are discussed.
Biological aortic valve replacement is recommended for patients older than 65 years1. In patients with small aortic roots, the implantation of a stented biological valve substitute based on the labelled size given by the manufacturer might not meet the functional needs. In this situation, Rahimtoola first described the prosthesis-patient mismatch (PPM) as follows: "mismatch can be considered to be present when the effective prosthetic valve area, after insertion into the patient, is less than that of a normal human valve"2. The effective orifice area of the valve prosthesis is to be related to the patient's body size and, more commonly, to the patient's body surface area. The hemodynamic consequence of a too-small prosthetic valve is an abnormally high transvalvular gradient3. It has been shown that the relationship between the transvalvular gradient and the effective orifice area indexed to the body surface area (EOAI) is curvilinear and that gradients increase exponentially when the indexed EOA is less than 0.8 to 0.9 cm2/m2. On the basis of this relation, an EOAI less than 0.85 cm2/m2 is generally regarded as the threshold for PPM in the aortic position4. The impact of the PPM on early and late clinical outcomes is controversial. However, it has been reported that PPM negatively affects the regression of left ventricular hypertrophy and thus the normalization of left ventricular function and the alleviation of symptoms4. Persistent left ventricular hypertrophy is associated with an increased risk of arrhythmias and sudden cardiac death5.
It is therefore advisable to avoid PPM as much as possible4. In the case of a predictable PPM for a planned aortic valve replacement with a biological valve substitute, the options are: 1) to accept the PPM resulting from the implantation of a stented pericardial valve when comorbidities of the patient forbid a more technically demanding operative technique to implant a larger prosthesis, 2) to enlarge the aortic root to accommodate a larger stented valve substitute6, or 3) to implant a stentless biological valve7 or homograft8.
Aortic root enlargement has been reported to enhance perioperative bleeding, necessitating a re-sternotomy and increasing early mortality9. Aortic homografts may have excellent hemodynamic profiles and good long-term outcomes when implanted by experienced surgeons8. However, their limited availability and the accelerated rate of calcification make aortic homografts less suitable biological valve substitutes than their counterpart, porcine stentless aortic xenografts10.
The shortage and drawbacks of homografts have prompted the conception and development of alternative biological valve substitutes. To this purpose, stentless aortic xenografts were introduced into clinical practice11. On one hand, thanks to the elimination of the cumbersome sewing ring, stentless aortic xenografts can reproduce the hemodynamic advantages of homografts. On the other hand, as a result of the application of anti-calcification technology, the durability of stentless aortic xenografts has been optimized to match and even exceed the longevity of homografts11. Hemodynamic advantages of stentless aortic xenografts are entirely attained by full-root implantation12. In contrast to subcoronary and root inclusion techniques, full-root implantation places the stentless aortic xenograft on top of the aortic annulus, and not inside it. This fact underlies the rationale to opt for the full-root implantation technique, which grants the implementation of the largest internal functional diameter of the stentless valve substitute. In addition, the preservation of the Valsalva sinuses en-bloc with the valve leaflets favors more physiological opening and closing movements and hence a longer life expectancy of the leaflets. This advantage further contributes to the amelioration of long-term results12.
However, concerns regarding the increased potential for bleeding and for the possible distortion of coronary ostia anastomoses prevent a number of cardiac surgeons from shifting from a classical aortic valve replacement with a stented biological valve to the more technically demanding procedure represented by full-root replacement with stentless aortic xenografts.
Given the potential hemodynamic advantages of stentless aortic xenografts, we have adopted full-root implantation to avoid PPM in patients with small aortic roots necessitating an aortic valve replacement (Table 1). In these patients, the aim is to attain a projected EOAI of greater than 0.85 cm2/m2 for the newly implanted aortic valve. This intention is based on the reports of Pibarot and co-workers showing an unacceptably high transvalvular gradients for valve substitutes having a projected EOAI of less than 0.85 cm2/m2, with the subsequent incomplete relief of symptoms and the persistent risk of adverse outcomes3,4. Following the initial identification of adult patients with an aortic annulus diameter of less than 20 mm on their pre-operative echocardiography, patients are further selected to have a body surface area of greater than 1.6 m2. In this subgroup of patients, the implantation of a 19-mm stented pericardial aortic valve (EOA: 1.28 cm2) would result in a projected EOAI of less than 0.85 cm2/m2. In this protocol, these patients are candidates for the full-root implantation of stentless aortic xenografts. The final decision is made intra-operatively after the removal of the aortic valve. If a 19-mm valve sizer for the stented pericardial aortic valve passes too-tightly through the aortic annulus and the patient is hemodynamically stable and can tolerate a longer operation, the full-root implantation of a stentless aortic xenograft is performed.
For the stentless aortic xenografts, we use two commercially available valve substitutes interchangeably (for details, see the Table of Materials). Both valves are procured from the porcine aortic root bearing the aortic valve. They are prepared using a low-pressure (0-2 mmHg) fixation process, with anti-calcification (e.g., XenoLogiX) treatment for one valve and alpha amino oleic acid (AOA) anti-calcification treatment for the other. In those patients for whom the 19 mm sizer for the stented pericardial valves passes too-tightly through the aortic annulus, the 23 mm sizer for the stentless aortic xenograft fitting well in the aortic annulus denotes that the stentless aortic xenograft size of 23 mm is to be chosen. This protocol describes in detail the technique of full-root implantation of stentless aortic xenografts, with emphasis on the management of the proximal suture line and coronary anastomoses. Limitations of this technique and alternative options are discussed.
The protocol follows the institutional guidelines of the human research ethics committee.
1. Pre-selection of the Patient
2. Preparation for Surgery
Note: Preparation for surgery follows institutional guidelines and recommendations for adult cardiac surgery patients.
3. Surgery
4. Postoperative Patient Care
Statistical analysis
The values of projected effective orifice area indexed to the body surface area (EOAI, cm2/m2) for implanted stentless aortic xenografts sized 23 mm are expressed as means ± SD and compared to the calculated EOAI of stented pericardial valves 4 mm smaller (i.e., 19 mm) using the non-parametric Mann Whitney test. In Table 2, continuous variables are compared using the non-parametric Mann Whitney test and categorical variables by Chi-square test. Statistical analysis is performed using commercially available software, with the statistical significance set at p<0.05.
Effective orifice area indexed
In patients with small aortic roots (Figure 1), the implantation of a 19 mm-sized stented pericardial valve would have resulted in moderate to severe PPM4 by an EOAI of 0.7 ± 0.09 (range 0.55 – 0.84) cm2/m2 (Figure 1). With this technique, the implantation of a stentless aortic xenograft in these patients yielded a significantly higher EOAI of 1.09 ± 0.14 cm2/m2 (range 0.87-1.31 cm2/m2, p <0.0001), thus eliminating any PPM (Figure 2).
Intraoperative and early postoperative data
As expected, the cross-clamp, cardio-pulmonary bypass, and operative times for the full-root implantation of stentless aortic xenografts in our patients were longer than those reported for isolated aortic valve replacement with stented valves13,14. Nevertheless, perioperative morbidity and mortality were very low and not adversely affected by the prolongation of the operative times (Table 2)13.
Figure 1: Internal Anatomy of the Heart. The anterior aspect of the heart is partially removed to depict the four cardiac chambers and valves. The anterior leaflet of the mitral valve is in continuity with the left and non-coronary cusps of the aortic valve. Please click here to view a larger version of this figure.
Figure 2: Effective Orifice Area Indexed. In patients with small aortic roots (N = 22), the projected effective orifice area indexed to the body surface area (EOAI, cm2/m2) for implanted stentless aortic xenografts sized 23 mm is significantly higher than the calculated EOAI if they had received a stented pericardial valve 4 mm smaller (i.e., 19 mm). The projected EOAI is calculated by dividing the effective orifice area (cm2) of the valve substitute provided by the manufacturer by the body surface area of the patient (m2). The values are expressed as means ± standard deviations.
Full root Stentless Xenografts | |
N | 22 |
Age, years (mean±SD) | 63±10 |
Female gender | 18 (82%) |
Body surface area, m2 (mean±SD) | 1.85±0.24 |
Ejection Fraction (%) (mean±SD) | 53±11 |
Aortic regurgitation | 5 (22%) |
Table 1: Patients' Characteristics. Patients' characteristics are depicted in this table. The decision to implant a full-root stentless aortic xenograft is based on the body surface area to avoid a projected effective orifice area of less than <0.85 cm2/m2, considered a prosthesis-patient mismatch.
Full-root Stentless Xenografts 23 mm | Isolated aortic valve replacement with stented pericardial valves1 | p | |
N | 22 | 36 | |
Cross-clamp time (min) | 83 ±9 | 62.3 ±9.4 | 0.0001 |
CPB time (min) | 134 ±32 | 101 ±27.2 | 0.0001 |
OP time (min) | 242±48 | 191.7 ±53.2 | 0.0001 |
Re-exploration for bleeding | 0 | 1(3%) | ns |
Pace maker | 0 | 0 | ns |
Stroke | 1(4.5%) | 1(3%) | ns |
Sternal infection | 0 | 0 | ns |
Early mortality | 0 | 1(3%) | ns |
1 Adapted with permission from Biomed Central from reference 13 | |||
ns = not significant |
Table 2: Comparison of Intraoperative Data and 30-day Morbidity and Mortality to Previously Reported Data. Cross-clamp, cardio-pulmonary bypass (CPB), and operative times are reported (mean values ± standard deviation), along with 30-day morbidity and mortality in the presented group of patients, and are compared with previously reported data for stented pericardial aortic valves. Adapted with permission from Biomed Central from reference13.
This study reports a detailed description of the surgical technique of full-root aortic valve replacement using stentless aortic xenografts in patients with small aortic roots. Early morbidity and mortality are very low and compare favorably with other reports7. Heavily calcified coronary ostia constitute an anatomical limitation to this technique. Another drawback to this technique is represented by patients with a poor general condition who would not tolerate longer operative times. In these cases, a standard stented pericardial aortic valve replacement, with or without aortic root enlargement, should be preferred to the more demanding full-root stentless aortic xenograft implantation6.
This protocol calls for six running 4/0 polypropylene sutures for the proximal anastomosis. Similarly to multiple interrupted sutures used by other authors14,15, this technique for the proximal anastomosis leads to a better distribution of tension on the proximal anastomosis and thus avoids pleating of the suture line. Compared to multiple interrupted sutures, the use of six semi-continuous running sutures is slightly time-saving. Moreover, it makes the use of reinforcement of the suture line by pericardial or polytetrafluoroethylene strips for the control of postoperative bleeding7,12,14 unnecessary. In these patients, no resternotomy was necessary for bleeding. A potential disadvantage of a single running suture for the proximal anastomosis advocated by some authors7,12 is the risk of pleating of the valve substitute and the left ventricular outflow tract.
Besides the potential of increased postoperative bleeding, coronary anastomotic problems constitute another major concern of cardiac surgeons who are not willing to use the full-root technique for the implantation of stentless aortic xenografts. Possible coronary anastomotic problems can arise, from kinking of patient's coronaries after re-implantation to tissue tear related to excessive tension on the anastomosis. To adapt the placement of the coronary neo-ostia of the graft to the coronary ostia of the patient, the left coronary neo-ostium is first created in the graft by extending the existing left coronary hole or ligated artery towards the commissure between the left and non-coronary sinus of the stentless graft. Upon completion of the proximal suture line and re-connection of the left coronary anastomosis, the place of re-connection of the right coronary ostium of the patient is adjusted according to the right coronary sinus of the graft. To do so, the right coronary neo-ostium in the graft is created by extending the existing right coronary hole or ligated artery towards the commissure between the right and non-coronary sinus of the stentless graft. Proximal mobilization over 1-2 cm of the main coronary arteries further helps in eliminating excessive tension on the coronary anastomoses and thus the potential for tissue tear and bleeding. This technique avoids the rotation of the stentless graft suggested by other authors12.
The cross-clamp, cardio-pulmonary bypass, and operative times for this technique are expectedly longer than those for standard aortic valve replacements with stented valves16. However, they compare favorably with those reported by Kunihara et al.7 for the full-root implantation of stentless aortic xenografts. Despite the prolongation of the operative times in our patients, the perioperative morbidity and mortality are not adversely affected, as compared to those reported in the STS Adult Cardiac Surgery database17 for isolated aortic valve replacement. In particular, the incidence of re-exploration for bleeding, complete heart block requiring definitive pace maker implantation, stroke, deep sternal infection, or early mortality are very low and similar to those reported by Kunihara et al.7 for the full-root implantation of stentless aortic xenografts and by ourselves for the isolated aortic valve replacement by stented pericardial valves13.
The labelled size of all commercially available mechanical and biological valve substitutes indicates the global (external) diameter of the valve. However, for stented valve substitutes, including mechanical and biological stented pericardial valves, the sewing ring of the valve occupies between 3 and 4 mm of the global (external) diameter of the valve and correspondingly reduces the functionally useful internal diameter. Biological stentless aortic xenografts are devoid of similar obstructive sewing rings. Hence, the functionally useful internal diameter of these valve substitutes is very close to their global (external) diameter as commercially labelled. As a result, for a given labelled size, biological stentless valves offer a functionally useful internal diameter larger than biological stented pericardial valves. A larger functionally useful internal diameter allows for a greater opening area of the valve, known as the effective orifice area of the valve. A better opening area of the valve, adjusted for the body surface area, known as the indexed effective orifice area, provides for superior hemodynamics and potentially for better functional relief of the patient. In this regard, a comparison between 23 mm stented and stentless valves implanted by the full-root technique showed better hemodynamics in the latter in terms of transvalvular gradients. As a consequence, better patient outcomes were observed in terms of regression of left ventricular hypertrophy18.
The selection of adult patients with small aortic roots for full-root stentless aortic xenograft implantation was based on the projected (i.e., preoperatively expected) EOAI. In concrete terms, in patients with an aortic annulus diameter of less than 20 mm, estimated on preoperative echocardiography, a subgroup with a body surface area of greater than 1.6 m2 was identified. These patients are at risk of PPM if they receive a stented pericardial valve offering an effective orifice area of 1.28 cm2, with a resulting indexed orifice area of 0.8 cm2/m2. It has been shown that projected EOAI of less than 0.85 cm2/m2 predicts PPM, with adverse effects on postoperative, long-term transvalvular gradients and patient outcomes3,4.
Another option to accommodate a larger aortic valve prosthesis into a small aortic root is represented by patch enlargement of the aortic annulus6. However, this technique is not devoid of drawbacks, even in experienced hands9. Increased postoperative bleeding requiring resternotomy and enhanced early mortality following patch enlargement of the aortic annulus have been reported by Sommers and David9.
In conclusion, in patients with small aortic roots, we recommend the full-root implantation of stentless aortic xenografts to avoid PPM. This technique can be performed without adversely affecting the early morbidity or mortality. The additional time necessary for the full-root implantation of stentless valves compared to the implantation of pericardial stented valves is therefore not detrimental to the early clinical outcomes and could be rewarded by better mid- and long-term outcomes. Limitations to this technique are represented by heavily calcified coronary ostia and patients in poor general condition who would not tolerate longer operative times.
The authors have nothing to disclose.
This work was supported by a grant from the Swiss Cardiovascular Foundation to RT.
Heart surgery infrastructure: | |||
Heart Lung Machine | Stockert | SIII | |
EOPA 24Fr. arterial cannula | Medtronic | 77624 | |
Atrial caval venous cannula 34/48Fr. | Medtronic | 93448 | |
LV vent catheter 17Fr. | Edwards | E061 | |
Antegrade 9Fr. cardioplegia cannula | Edwards | AR012V | |
Retrograde 14Fr. cardioplegia cannula | Edwards | NPC014 | |
Coronary artery ostial cannula 90° | Medtronic | 30155 | |
Coronary artery ostial cannula 45° | Medtronic | 30255 | |
Name | Company | Catalog Number | Comments |
Valve subsitutes: | |||
Stentless aortic xenograft Prima Plus 23mm | Edwards | 2500P-23 | anti-calcification XenoLogiX treatment |
Stentless aortic xenograft Sizer 23mm | Edwards | 1170 | |
Stentless aortic xenograft Freestyle 23 mm | Medtronic | FR995-23 | alpha amino oleic acid (AOA) anti-calcification treatment |
Stentless aortic xenograft Sizer 23mm | Medtronic | 7900 | |
Electrocautery | Covidien | Force FXTM | |
Name | Company | Catalog Number | Comments |
Sutures: | |||
Polypropylene 4/0 | Ethicon | 8871H | |
Polypropylene 5/0 | Ethicon | 8870H | |
Polypropylene 6/0 | Ethicon | EH7400H | |
Braided polyesther 2/0 ligature with polybutylate coating | Ethicon | X305H | |
Micro knife Sharpoint | TYCO Healthcare PTY | 78-6900 | |
Name | Company | Catalog Number | Comments |
Drugs: | |||
Midazolam | Roche Pharma | N05CD08 | |
Rocuronium | MSD Merck Sharp & Dohme | M03AC09 | |
Propofol | Fresenius Kabi | N01AX10 | |
Fentanil | Actavis | N01AH01 | |
Heparin | Braun | B01AB01 | |
Protamin | MEDA Pharmaceutical | V03AB14 | |
Name | Company | Catalog Number | Comments |
Instruments: | |||
Cooley vascular aortic clamp | Delacroix-Chevalier | DC40810-16 | |
Dissection forceps Carpentier | Delacroix-Chevalier | DC13110-28 | |
Scissors Metzenbaum | Delacroix-Chevalier | B351751 | |
Needle holder Ryder | Delacroix-Chevalier | DC51130-20 | |
Dissection forceps DeBakey | Delacroix-Chevalier | DC12000-21 | |
Micro needle holder Jacobson | Delacroix-Chevalier | DC50002-21 | |
Micro scisors Jacobson | Delacroix-Chevalier | DC20057-21 | |
Lung retractor | Delacroix-Chevalier | B803990 | |
Allis clamp | Delacroix-Chevalier | DC45907-25 | |
O’Shaugnessy Dissector | Delacroix-Chevalier | B60650 | |
18 blade knife | Delacroix-Chevalier | B130180 | |
Leriche haemostatic clamp | Delacroix-Chevalier | B86555 | |
Name | Company | Catalog Number | Comments |
Data analysis: | |||
Mann-Whitney and Chi-square tests | GraphPad | Prism 7 |