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Eur J Cardiothorac Surg 2008;33:554-559. doi:10.1016/j.ejcts.2007.12.053
Copyright © 2008, European Association for Cardio-thoracic Surgery. Published by Elsevier. All rights reserved.
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Stentless full root bioprosthesis in surgery for complex aortic valve-ascending aortic disease: a single center experience of over 300 patients

Otto E. Dapunt*, Jerry Easo, Philipp P.F. Hölzl, Peter Murin, Michael Südkamp, Michael Horst, Ehsan Natour

Department of Cardiothoracic Surgery, Klinikum Oldenburg, Dr Eden Street 10, 26133 Oldenburg, Germany

Received 15 September 2007; received in revised form 15 December 2007; accepted 20 December 2007.

* Corresponding author. Tel.: +49 441 403 2820; fax: +49 441 403 2830. (Email: dapunt.otto{at}klinikum-oldenburg.de).


   Abstract
Top
 Abstract
1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
 Appendix A
 References
 
Objective: The technically demanding full root aortic valve replacement necessitating coronary ostia reimplantation apparently leads to hesitation by some surgeons despite the superior hemodynamics and excellent long-term clinical performances of the stentless xenografts. Clinical data of stentless full root replacements was retrospectively analyzed in this perspective for validation. Methods: From November 1999 to March 2007, 317 adult patients (male: 196, female, 121) underwent modified Bio-Bentall procedure using the Medtronic Freestyle xenograft as a full root replacement. Two hundred and three patients received an isolated root replacement or a root and ascending aortic replacement (ARR). In 114 patients a variety of concomitant procedures including coronary artery bypass grafting (n = 32), mitral valve repair (n = 11) and aortic arch replacement (n = 36) were performed. (ARR+). Results: Mean patient age was 70.3 ± 10.2 years (range 17–94 years), 97 patients were 75 and older at time of procedure. Mean operative time for the ARR was 190 ± 57 min with a clamp time of 88 ± 27 min. Mean operative time for ARR+ group was 282 ± 93 min with an average clamp time of 110 ± 32 min. Overall operative mortality was 7.9% (25/317), for ARR it was 5.4% (11/203). Mean ICU stay was 4.9 ± 8.1 days, mean hospital stay being 9.8 ± 8.1 days. Necessity for bailout bypass surgery among patients with ARR was low at 1.5% (3/203) comparable to stented xenograft implantations. Echocardiography demonstrated excellent clinical results with low transvalvular gradients especially when a single suture inflow anastomosis technique was used. Conclusions: Full root stentless valve implantation preserving porcine root integrity is a valuable option in aortic valve/ascending aorta surgery. Though technically a more challenging operation, it does not lead to increased perioperative morbidity and mortality and can be beneficial mainly for elderly patients with small aortic roots with or without aortic root pathology.

Key Words: Aortic valve replacement • Stentless valves • Full root technique


   1. Introduction
Top
 Abstract
 1. Introduction
2. Patients and methods
 3. Results
 4. Discussion
 Appendix A
 References
 
The development of stentless xenografts primarily benefited the elderly patient with aortic stenosis [1]. The stentless design allows implanting valve prostheses with larger effective orifice area by removing the obstructive element of the stent in the aortic root, and thus theoretically reducing stress on the xenograft cusp when suspended from a rigid frame in a stented bioprosthesis [2]. Stentless valves, namely the St. Jude Medical (SJM) Toronto Root Bioprosthesis (St. Jude Medical, Inc., St. Paul, Minn) and the Edwards Prima Plus stentless porcine bioprosthesis (Edwards Lifesciences, Irvine, CA) have demonstrated excellent hemodynamic and clinical results and are implanted routinely in valve surgery at present [3].

The Medtronic Freestyle aortic root bioprosthesis (Medtronic Inc. Minneapolis, MN) is the preferred biological valve substitute for root replacement in our institution. It is a stentless porcine aortic root prepared by using a zero-pressure fixation process and anticalcification treatment using alpha-amino oleic acid (AOA) that aims to optimize both hemodynamic properties and durability of the biological prosthesis. Several clinical studies have demonstrated excellent clinical performance of this stentless valve over the last decade [1,2,4–6]. The device can be implanted in various techniques namely as a subcoronary valve replacement, as a root inclusion, or as a complete aortic root replacement. Recent studies by the Freestyle Valve Study Group have demonstrated the full root implantation of the valve prosthesis to be associated with a larger effective orifice area (EOA) and lower gradients, a lower prevalence of aortic regurgitation and better functional NYHA class on follow-up [7].

In aortic valve and root surgery, the full root replacement technique is believed to be superior because of the resultant hemodynamic characteristics especially in the small aortic annulus. It is, however, associated with higher operative morbidity and mortality, with anticipated prolonged myocardial ischemia and increased operative bleeding complications [8,9]. Bach et al. [7] demonstrated that the operative mortality and perioperative risks of a full root implantation of stentless aortic valve are substantially reduced with increasing experience. However, some surgeons still hesitate to employ this technique due to increased technical requirements, including reimplantation of the coronary ostia.

This retrospective study analyzes our single center experience concerning the early- and mid-term results of the stentless xenograft implanted solely in a full root fashion in patients with aortic root pathology or with small aortic root where a stented bioprosthesis implantation would had led to patient-prosthesis mismatch.


   2. Patients and methods
Top
 Abstract
 1. Introduction
 2. Patients and methods
3. Results
 4. Discussion
 Appendix A
 References
 
From November 1999 to March 2007, 317 patients received a full root Freestyle aortic root bioprosthesis at our institution.

2.1 Operative technique
The aorta was transected above the sinotubular ridge after mobilizing the aorta. The remaining tissue of the sinuses of Valsalva and the diseased aortic valve were removed. The coronary ostia were mobilized in a button fashion. After sizing the aortic annulus the proximal anastomosis was performed using 20–25 single interrupted sutures of 4-0 braided Dacron placed in a single plane. The inflow anastomosis has been performed in this manner since May 2005. Earlier, the method of choice was a series of pledgetted 2-0 braided Dacron mattress sutures placed from the ventricular to the aortic aspect of the annulus for epiannular fixation of the prosthesis.

After the proximal suture line was completed, the mobilized coronary buttons were implanted in an end-to-side fashion to the corresponding sinus of Valsalva using a continuous 5-0 polypropylene suture. Finally, the cranial end of the bioprosthesis was sewn end-to-end to the aorta with a continuous 4-0 polypropylene suture to complete the root replacement. If further resection of the ascending aorta was required due to calcification or aneurysmatic dilatation or dissection, a vascular tube graft was interposed (Vascutek, Renfrewshire, Scotland). Further concomitant surgery, if necessary, was performed then in standard manner.

In the immediate postoperative period heparin was administered for one week intravenously, followed by administration of low molecular weight heparin (Dalteparin) for 2 weeks. If warfarin was not warranted, 100 mg of aspirin daily was the anticoagulation therapy recommended for the long-term.

2.2 Clinical and echocardiographic data
Preoperative clinical and operative data were prospectively recorded for all patients. The patients were monitored throughout the postoperative period according to the guidelines of The Society of Thoracic Surgeons and the American Association of Thoracic Surgeons for documentation of adverse events [8]. Operative mortality was defined as mortality within 30 days or within one hospital stay after the operation [even exceeding 30 days] while 30-day mortality included all deaths within 30 days after the operation.

Echocardiograms were performed routinely by the cardiologist at the investigational center on the 5th postoperative day using standard criteria for analysis. Mean pressure gradient was calculated using the modified Bernoulli's equation, correcting for proximal velocity. Aortic regurgitation was reported as absent, trivial, mild, moderate or severe on standard criteria including assessment of jet width, circumference and eccentricity.

2.3 Statistical analysis
Continuous data were expressed as mean ± 1 SD. Categorical data were expressed as percentages. Estimates for survival and incidence of valve related complications were calculated using the Kaplan–Meier method. Statistical analysis was performed using SPSS 13.0 statistical software.


   3. Results
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
4. Discussion
 Appendix A
 References
 
Of 317 patients, 196 were men (62%) and 121 were women (38%). The mean age was 70.2 ± 10.2 (range 17–94) years. Ninety-seven patients (30.6%) were older than 75 years of age. Preoperative risk factors are shown in Table 1 . The valve size distribution is detailed in Table 2 , with 21 mm being the smallest size implanted. Indications for aortic valve replacement with the stentless xenograft included annulo-aortic ectasia or aneurysm of the aortic root, ascending aorta and aortic arch in 139 patients (43.8%), active endocarditis in 21 patients (6.6%), aortic dissection type Stanford A in 14 patients (4.4%) and aortic root sclerosis/small aortic annulus in 143 patients (45.2%). Concomitant procedures are described in Table 3 .


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  		Table 1 Preoperative risk factors
 

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  		Table 2 Valve size distribution and mean transvalvular gradients on postoperative day 5 (mattressed sutures vs single suture technique)
 

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  		Table 3 Incidence of concomitant procedure
 
Isolated full root replacement or replacement of the aortic root and the ascending aorta with a Dacron vascular tube graft was performed in 203 patients (ARR group). Mean aortic cross-clamp time for ARR group was 88 ± 27 min, operative time being 190 ± 57 min. When a concomitant procedure was performed (ARR+ group) mean aortic cross-clamp time was 110 ± 32 min, operative time 282 ± 93 min. The prolonged aortic cross-clamp time can be explained by the extensive decalcification necessary for the use of this technique, the consequent use of simple interrupted sutures and the learning curve with the initial experience for this technically more challenging surgery. The necessity for bailout bypass surgery in the ARR group, i.e. coronary bypass grafting in patients (not suffering from coronary heart disease) with possible coronary insufficiency after reimplantation, was low at 1.5% (3/203). In the immediate postoperative period five patients (1.6%) had renal dysfunction requiring dialysis, 10 patients (3.1%) presented with permanent neurological impairment (stroke). Rethoracotomy for bleeding had to be performed in 30 patients (9.5%). This rather large number resulted from the rigorous rethoracotomy indications pursued at our institution with re-exploration after a drainage loss of 500 ml over the first 6 h postoperatively. Internal analysis of the last 37 patients undergoing isolated aortic root replacement with use of a novel anastomotic sealant (CoSeal, Cohesion Technologies, Palo Alto, CA) demonstrated a significant reduction of postoperative bleeding with a rethoracotomy rate of only 2.7%. The high percentage of rethoracotomies, however, was not associated with a significant increase in mortality and morbidity in overall operative results. Postoperative echocardiography data routinely obtained on the 5th postoperative day showed low transvalvular gradients even in small prosthetic sizes (Table 2). Mean ICU stay was 4.9 ± 8.1 days, mean hospital stay 9.8 ± 8.1 days.

Follow-up extended up to 7.4 years, (average 2.2 years) and a total of 657 patient-years. It was 100% complete .The overall mortality for the whole series during 7.4 years was 16.1% (51/317). Thirty-day mortality for the whole series was 6% (19/317) and hospital mortality was 7.9% (25/317). The actuarial survival rate at 5 years was 77% (Fig. 1 ). Freedom from endocarditis was 93% (Fig. 2 ) at 5 years. Two patients underwent successful reoperations for late prosthetic endocarditis in our clinic at 50 and 56 months postoperatively. In both patients a second Medtronic bioroot could be successfully reimplanted with excellent clinical performances to date. A third patient reoperated for prosthetic endocarditis in another clinic died within the hospital stay after the reoperative procedure. Another three patients were treated conservatively for endocarditis. Freedom from aortic valve reoperation and freedom from structural valve deterioration were 99% and 100% at 5 years (Fig. 3 ). Freedom from thromboembolic complications was 100% at 7 years. No patient exhibited any sign of significant aortic regurgitation at any time during the follow-up.


Figure 1
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  		Fig. 1. Freedom from death isolated ARR versus ARR plus concomitant surgery.

 

Figure 2
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  		Fig. 2. Freedom from endocarditis for all patients.

 

Figure 3
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  		Fig. 3. Freedom from reoperation for all patients.

 
Isolated ARR group had an average follow-up of 2.4 years and a total of 449 patient-years. The actuarial survival rate of ARR group at 5 years was 81% (Fig. 1). In the isolated ARR group, hospital mortality was 5.4% (11/203), 30-day mortality being 3.4% (7/203). Overall mortality at 7.4 years for ARR group was 12.8% (26/203).


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
Appendix A
 References
 
Stentless valves have demonstrated superior hemodynamic characteristics when compared to the stented prostheses [1–6]. Transvalvular gradients remained low on exercise. Rapid regression of left ventricular hypertrophy and increase of the effective orifice area were achieved by eliminating the rigid ring in the left ventricular outflow tract (LVOT) [11,12].

Multicenter study groups investigated the impact of three different methods of Freestyle valve implantation. They noted superior hemodynamic profile, better functional class and freedom from aortic regurgitation on using the full root replacement technique [7]. However, attendant higher operative mortality, with anticipated prolonged myocardial ischemia and increased bleeding complications [5,6,8–10,13,14] associated with this technique makes it technically daunting for several surgeons. This technique involves an inflow suture line, two coronary buttons implantation lines and an aortic reapproximation suture line [5]. In contrast, in most circumstances, a stented xenograft only involves an inflow suture line and an aortic closure suture line. Expected prolonged cardiopulmonary bypass time, however, did not lead to increased mortality or morbidity despite the increased number of suture lines and greater technical challenges. Perioperative risk of the full root replacement has been noted to decrease substantially with increasing surgical experience [7].

At our institution, the full root technique has been the method of choice of implantation when using a stentless root bioprosthesis. It accommodates sufficiently large valve prosthesis, even in cases of small aortic annulus or heavily calcified aorta [15–16]. Among 317 patients there was no need for aortic root enlargement obviating any additional perioperative mortality and morbidity [17], while patient-prosthesis mismatch could be avoided by upsizing the prosthesis especially in small aortic annulus. The root replacement technique maintains the root geometry and the integrity of the functional entity of leaflet, sinus and root. We believe these characteristics improve the durability of the bioprosthetic valve and we prefer to use this method instead of classic Bentall procedure. Recent studies on the long-term performance of stentless valves implanted in a subcoronary position have shown increased aortic regurgitation from incompetent valve closure due to increased dilatation of the sinotubular junction over time [18]. These problems can be avoided by the aforementioned technique. Late follow-up of our patients demonstrated no aortic regurgitation at all.

Several physiologic and pathological consequences of a progressive dilation influence the size of the ascending aorta as a determinant for replacing the ascending aorta on an elective basis. Current recommendations for elective resection are variable. Pre-emptive surgical therapy is recommended at 5.5 cm for ascending aortic aneurysms [19]. The rate of expansion is also an important factor, with a rate of greater than 1.0 cm per year being an accepted indication for surgery [20]. With more experience we have now become more liberal about replacement of the aortic root or ascending aorta even when the diameter is under 5.0 cm depending on the aortic wall quality. It can also be beneficial in cases of heavy sclerosis of the aortic root or in small aortic annulus with inherent danger of patient-prosthesis mismatch. Our operative experience of a large number of root replacements performed at the single center with no significantly increased perioperative risk supports the decision to intervene prophylactically, thus reducing the risk of rupture or dissection. Patients suffering from severe aortic valve disease and aortic root/ascending aorta enlargement represented the largest group undergoing valve replacement with the bioroot. The Freestyle valve has already been demonstrated to be a viable option in endocarditis and aortic dissection [21].

Bioroot implantation with single suture technique as described by Kon et al. [9] and used by us since May 2005, is believed to allow placement of the valve prosthesis with no narrowing of the LVOT and no obstruction by any rigid structures such as pledgets, which possibly play a role in non-structural dysfunction leading to reoperations. Use of this technique was prompted by the incidental experience of an immediate postoperative gradient of 35 mmHg in the intraoperative echocardiographic examination in one patient after uneventful implantation of a Medtronic Freestyle valve size 23 mm. On closer investigation, LVOT narrowing caused by the purse-string effect of the mattressed sutures could be demonstrated. After reimplantation of the stentless bioroot using the single interrupted sutures it was possible to achieve a mean transvalvular gradient of 7 mmHg. The further hospital stay was uneventful with an excellent clinical performance of the valve at 2 years. Based on this experience, we changed our operative technique, which resulted in further reduction of postoperative transvalvular gradients (Table 2).

Coronary orientation sometimes poses problems for reimplantation of the coronary ostia, as there may be a discrepancy of up to 30–60° in distance between the porcine coronary ostia and the human coronary arteries. This problem is solved by some surgeons by rotating the valve to anastomose the human left coronary button with the noncoronary sinus of the prosthesis, turning the left porcine coronary ostium towards the right human coronary artery [5]. This technique had to be applied infrequently in this series of patients. In most cases it was preferred to anastomose the right coronary ostium with the right prosthesis sinus either by creating a new opening closer to the commissure between the right and the noncoronary cusp or by using the site of the natural offspring of the porcine right coronary artery. Bailout bypass surgery had to be performed in three patients, all undergoing isolated bioroot replacement. In two cases there was right coronary insufficiency due to problems from suturing heavily calcified right coronary buttons. In another patient the left coronary artery anastomosis was compressed by the pulmonary trunk. All patients received coronary-saphenous vein bypass grafting during the same operation. All three patients with the unplanned bailout coronary surgery survived the operative procedure, similar to other reports [9,22]. Coronary revascularization should be performed rapidly when ventricular dysfunction or characteristic ECG abnormalities suggestive of coronary artery flow disturbance is encountered upon weaning from cardiopulmonary bypass.

Operative mortality and morbidity with the Freestyle bioroot were acceptably low. The hemodynamic characteristics were excellent, with mean transvalvular gradients of 11.3 mmHg for sizes 23–29. In the sizes 27 and 29 mm a mean gradient of 10 mmHg or less could be achieved. Upsizing of the aortic root was regularly possible by at least one size, allowing optimal postoperative hemodynamics for all patients.

The long-term performance of the stentless bioroot has been adequately demonstrated by freedom from reoperation and freedom from endocarditis in the multicenter studies. The durability of the xenograft with its specific AOA anticalcification treatment will be a matter of interest in the coming years. To date, electron beam CT studies have shown no excess calcification of the aortic wall or calcification of the coronary suture lines, when compared to homografts [23,24].

In conclusion, excellent hemodynamics with low gradients at acceptable operative risk can be achieved by full root stentless valve replacement. Operative experience in our high volume clinical institution prompts us to recommend the use of the stentless bioroot even for patients with minor abnormalities of the aortic root. Patients with small aortic annulus appear to benefit from avoidance of patient-prosthesis mismatch. A bioroot is a valuable option for elderly patients since reoperations for structural valve degeneration is very unlikely in view of the excellent 10-year results [5]. Experience with reoperation for replacing a bioroot is very limited and may well be associated with increased morbidity and mortality due to expected problems with coronary isolation and reanastomosis. Further long-term studies are necessary to verify the anticipated prolonged durability of the bioprosthetic root.


   Appendix A
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
 Appendix A
References
 
Conference discussion

Dr C. Yankah (Berlin, Germany): I would like to ask you one question. Which the implantation technique did you use? A free-standing aortic root replacement or an inclusion technique? The second question is; what was the pathology of the aortic root at reoperation?

Dr Dapunt: We didn’t use the inclusion technique with this kind of prosthesis at all. We always remove the entire ascending aorta or aortic root, whatever has to be replaced, and isolate the coronary arteries with small buttons. As I have shown you, we use a single interrupted suture technique for the inflow anastomosis and a button technique with continuous sutures for the coronary arteries.

The second question was? I didn’t understand it correctly.

Dr Yankah: The pathology at the reoperation, the aortic root pathology at the reoperation. Was the root tissue soft or calcified?

Dr Dapunt: I only have personal experience of three patients reoperated, all of them for prosthetic endocarditis, five to seven years after implantation. Two patients are out of this series, one was operated elsewhere. These roots were rather stiff, but it was rather easy to divide the coronary ostia since the color of the coronary ostia is usually lighter and the color of the Freestyle root valve tends to be a little darker yellow. Of course, the tissue is stiff but in none of these cases was it ever heavily calcified.

Dr T. Orszulak (Rochester, MN): Two questions. Is it appropriate to use this graft in endocarditis since there is a Dacron buttress on the lower part of the prosthesis? And secondly, your median follow-up was 2.4 years, so your third point is not really supported by your data.

Dr Dapunt: Well, the third point is based on the data published so far with longer follow-up times. I think this is one of the choices for valve replacement in acute endocarditis, because it is mainly constructed of biological material with only a small aspect of a tubular coating.

The reinfection rate is low, and this can usually be very sufficiently treated with antibiotics, which is different to stented bioprostheses.

Dr J. Ennker (Lahr, Germany): When do you use the full root technique and when do you use the subcoronary technique and what is the percentage of stentless valves of all your biological valves?

Dr Dapunt: The percentage I don’t know exactly, but it is rather high. Whenever we decide to put in such a tubed stentless prosthesis, we always use the full root technique. If we use the subcoronary technique, we prefer to implant another prosthesis like the Sorin Freedom Solo valve because it is much easier with much less trouble to be implanted, or if patient-prosthesis mismatch is not to be expected, then we would still use a stented valve. Among all our biological valve replacements, about 50–60% stentless valves are implanted.

Dr J. Pepper (London, United Kingdom): Your mortality is separated into operative and 30-day mortality, which I didn’t quite understand. Does the 30-day correspond to the period after the operation after 30 days and should it therefore be added to the operative mortality for the full 30-day mortality?

Dr Dapunt: No, it has been added. We define 30-day mortality as all deaths occurring within 30 days after the operation. Operative mortality or maybe better termed hospital mortality includes all deaths within 30 days or within one continuous hospital stay.


   Footnotes
 
{star} Presented at the 21st Annual Meeting of the European Association for Cardio-thoracic Surgery, Geneva, Switzerland, September 16–19, 2007.


   References
Top
 Abstract
 1. Introduction
 2. Patients and methods
 3. Results
 4. Discussion
 Appendix A
 References
 

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Otto E. Dapunt
Jerry Easo
Michael Horst
Ehsan Natour
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