Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience

Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience

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Heart, Lung and Circulation (2015) xx, 1–7 1443-9506/04/$36.00 http://dx.doi.org/10.1016/j.hlc.2015.05.011


Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience Andrew G Sherrah, MBBS a,b, Richmond W Jeremy, PhD FRACP a,b,c, Rajesh Puranik, PhD FRACP a,c, Paul G Bannon, PhD FRACS a,b,d,e, P Nicholas Hendel, FRACS b,d, Matthew S Bayfield, FRACS b,d, Michael K Wilson, FRACS b,d,f, Peter W Brady, FRACS g, David Marshman, FRACS g, Manu N Mathur, FRACS g, R John Brereton, FRACS g, James R Edwards, FRACS h, Robert G Stuklis, FRACS h, Michael Worthington, FRACS h, Michael P Vallely, PhD FRACS a,b,d,f* a

Sydney Medical School, University of Sydney, Sydney, NSW, Australia The Baird Institute for Applied Heart and Lung Surgical Research, Sydney, Australia c Department of Cardiology, Royal Prince Alfred Hospital, Sydney, NSW, Australia d Department of Cardiothoracic Surgery, Royal Prince Alfred Hospital, Sydney, NSW, Australia e Institute of Academic Surgery, Royal Prince Alfred Hospital, Sydney, NSW, Australia f Australian School of Advanced Medicine, Macquarie University, Sydney, NSW, Australia g Department of Cardiothoracic Surgery, Royal North Shore Hospital, Sydney, NSW, Australia h Darcy Sutherland Cardiothoracic Surgical Unit, Royal Adelaide Hospital, Adelaide, SA, Australia b

Received 24 March 2015; received in revised form 30 April 2015; accepted 6 May 2015; online published-ahead-of-print xxx


The Freestyle stentless bioprosthesis (FSB) has been demonstrated to be a durable prosthesis in the aortic position. We present data following Freestyle implantation for up to 10 years post-operatively and compare this with previously published results.


A retrospective cohort analysis of 237 patients following FSB implantation occurred at five Australian hospitals. Follow-up data included clinical and echocardiographic outcomes.


The cohort was 81.4% male with age 63.213.0 years and was followed for a mean of 2.42.3 years (range 0-10.9 years, total 569 patient-years). The FSB was implanted as a full aortic root replacement in 87.8% patients. The 30-day all cause mortality was 4.2% (2.0% for elective surgery). Cumulative survival at one, five and 10 years was 91.71.9%, 82.83.8% and 56.510.5%, respectively. Freedom from re-intervention at one, five and 10 years was 99.50.5%, 91.63.7% and 72.310.5%, respectively. At latest echocardiographic review (mean 2.32.1 years post-operatively), 92.6% had trivial or no aortic regurgitation. Predictors of post-operative mortality included active endocarditis, acute aortic dissection and peripheral vascular disease.

*Corresponding author at: Suite 209, 100 Carillon Avenue, Newtown NSW 2042, Australia. Tel.: +61 2 9422 6090; fax: +61 2 9422 6099, Email: [email protected] © 2015 Australian and New Zealand Society of Cardiac and Thoracic Surgeons (ANZSCTS) and the Cardiac Society of Australia and New Zealand (CSANZ). Published by Elsevier Inc. All rights reserved.

Please cite this article in press as: Sherrah AG, et al. Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience. Heart, Lung and Circulation (2015), http://dx.doi.org/10.1016/j.hlc.2015.05.011

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We report acceptable short and long term outcomes following FSB implantation in a cohort of comparatively younger patients with thoracic aortic disease. The durability of this bioprosthesis in the younger population remains to be confirmed.


Aortic valve  Heart valve prosthesis  Bioprosthesis  Aorta  Thoracic  Aortic Aneurysm

Introduction The choice of valvular prosthesis in aortic valve replacement surgery must be tailored to the needs of the individual patient. Younger patients with thoracic aortopathy wish to avoid the need for lifelong anticoagulation, necessary with mechanical valve implantation, however, long-term durability remains a concern [1–5]. The Freestyle stentless bioprosthesis (FSB; Medtronic Pty. Ltd.) is a porcine aortic bioprosthesis particularly suitable for use where concurrent aortic root replacement surgery is necessitated by thoracic aortic disease. Long-term clinical and echocardiographic data are available up to 15 years post-operatively for the Freestyle, with promising results evident thus far [6–8]. We report the multicentre clinical and echocardiographic outcomes up to 10 years post-operatively following the use of the FSB for aortic valve and root surgery in a cohort of comparatively younger patients [7–9].

Patients and Methods Study Group From January 2004 until July 2014, 249 patients underwent FSB implantation in the aortic position at five Australian hospitals (Royal Prince Alfred Hospital, Royal North Shore Hospital, Macquarie University Hospital and Strathfield Private Hospital, in Sydney, New South Wales; and Royal Adelaide Hospital, in Adelaide, South Australia). All patients were included in this study except for 12 patients who had long-term follow-up conducted overseas, and for whom complete data was not available. The study timeframe was chosen so that the use of the FSB across all institutions was standardised (following its approval for use in Australia in 1996) excluding a period (>1 year) of introduction of the new technique (mean 3.41.9 years, range 1.0-6.0 years).

Data Collection All patients had pre-operative demographic and clinical data collected, including age at operation, gender, indication for aortic valve/root surgery, major co-morbidities, previous cardiac or aortic surgery, and New York Heart Association (NYHA) Heart Failure Class. Operative data included concomitant cardiac or aortic interventions and implanted valve size. The surgical approach was recorded, as three different techniques for FSB implantation were used, each with differing associated predicted surgical risks [10,11]. These included aortic valve replacement alone (in the sub-coronary position), an aortic root inclusion technique and full aortic

root replacement (with coronary artery re-implantation), as well as varying levels of replacement of the remaining ascending aorta and aortic arch. Aortic hemi-arch replacement was defined as surgical replacement up to the distal ascending aorta necessitating an ‘open’ distal anastomosis be performed (typically with deep hypothermic circulatory arrest). Patients were followed up by annual clinical review. Postoperative clinical data was collected and reported according to existing guidelines [12] and included all-cause 30-day mortality, operated valve re-intervention (including coronary artery bypass graft surgery, CABG, and percutaneous coronary artery intervention), structural valve deterioration (SVD), operated valve endocarditis, bleeding events (including acute post-operative bleeding), need for therapeutic anticoagulation (with warfarin or a novel anticoagulant), cerebrovascular accident (CVA) and NYHA class at last follow-up. All post-operative information was obtained from clinical review by the operating surgeon, referring cardiologist and/or general practitioner on an annual basis. Where available, echocardiographic data were collected from within one month, six months and one year post-operatively, and yearly thereafter. The presence of implanted aortic valve regurgitation (AR), as well the mean prosthetic transvalvular aortic gradient, was recorded.

Ethical Approval The retrospective collection of this data was approved by the local ethics committee.

Data Analysis Statistical analysis was performed using SPSS Version 22 statistical software (SPSS Inc., Chicago, IL.). Continuous variables are described as a mean  standard deviation. Categorical variables are described as absolute and relative frequencies (percentage). Survival and re-intervention data are presented using the Kaplan-Meier actuarial technique for probability estimation over time. A Chi square test was used to compare NYHA Class pre- and post-operatively. A Cox proportional hazard model was used to identify individual pre-operative and intra-operative predictors of survival and re-intervention. A two-tailed p value less than 0.05 is reported significant.

Results Mean patient age was 63.213.0 years and 77 patients (32.5%) were younger than or equal to 60 years of age. Males accounted for 81.4% of patients. Mean post-operative

Please cite this article in press as: Sherrah AG, et al. Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience. Heart, Lung and Circulation (2015), http://dx.doi.org/10.1016/j.hlc.2015.05.011

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Table 1 Pre-operative patient characteristics and co-morbidities.

Table 2 Indications for surgery. Indication for aortic valve/root surgery; n (%)



Number Male sex; n (%)

237 193 (81.4)

Mean age; years  SD

63.2  13.0

Risk factors; n (%) Hypertension

191 (80.6)


124 (52.3)

Ischaemic heart disease

75 (31.7)

History of acute myocardial

13 (5.5)

infarction Congestive heart failure

74 (31.2)

History of endocarditis

18 (7.6)

(including active) History of arrhythmias Atrial arrhythmia Ventricular arrhythmia Carotid vascular disease

47 (19.8) 45 (19.0) 2 (0.8) 9 (3.8)

(ultrasound diagnosis) Peripheral vascular disease

28 (11.8)

Diabetes mellitus

26 (11.0)

History of cerebrovascular disease

21 (8.9)

Chronic airways disease

53 (22.4)

Chronic renal impairment

22 (9.3)

(plasma creatinine >120 mmol/L) Prior cardiac surgery; n (%) Aortic valve replacement  CABG Aortic root replacement  CABG

Annulo-aortic ectasia or aortic root aneurysm Stanford type A aortic dissection

176 (74.3) 22 (9.3)

Aortic stenosis  aortic root calcification

16 (6.8)

Aortic valve endocarditis  aortic root abscess

15 (6.3)

Prosthetic aortic valve dysfunction

7 (3.0)

Isolated aortic valve regurgitation

1 (0.4)

Freestyle implantation with additional replacement of the ascending aorta and/or the aortic arch (Table 3). Other concomitant surgery is listed in Table 3. The group included 31 patients (13.1%) who required a redo sternotomy owing to previous cardiac surgery (Table 1). The most commonly used bioprosthesis size was 27 mm (32.5%) (Table 3). Preoperatively, 31.7% of patients were in NYHA Class III or IV (Figure 1).

Short Term All-cause 30-day mortality for the entire cohort was 4.2%. For patients undergoing elective surgery, the all-cause 30-day mortality was 2.0%. Within the entire group, there were 10 early deaths; the causes of early death were cardiac failure

31 (13.1) 17 (7.2) 3 (1.3)

Ascending aorta replacement

4 (1.7)

Aortic coarctation repair

3 (1.3)

CABG only

2 (0.8)


2 (0.8)

Abbreviations: CABG, coronary artery bypass graft surgery; SD, standard deviation.

follow-up was 2.42.3 years (range 0.0-10.9 years; total follow-up 569 patient-years). Follow-up was 100% complete to within 18 months of the date of study completion and 85% complete to within 12 months. Pre-operative patient characteristics and co-morbidities are listed in Table 1. A history of ischaemic heart disease was present in 31.7%, 8.9% had a history of cerebrovascular disease, and 9.3% had a history of chronic renal impairment. Fifteen patients (6.3%) took an oral anti-coagulant pre-operatively. The most common indications for surgery included annulo-aortic ectasia or aortic root aneurysm (74.3%), Stanford type A aortic dissection (9.3%), aortic stenosis (with or without aortic root calcification) (6.8%), and active endocarditis (6.3%) (Table 2). The surgery was deemed elective in 200 patients (84.4%), with the remaining patients being either urgent or emergent cases. The FSB was implanted as a full aortic root replacement in 87.8% of patients. The majority of patients (75.5%) underwent

Table 3 Intra-operative patient data. Variable


Operative approach; n (%) Full root replacement

208 (87.8)

Sub-coronary implantation

18 (7.6)

Root inclusion implantation

11 (4.6)

Freestyle bioprosthesis size; n (%) 19mm

1 (0.4)


13 (5.5)


31 (13.1)

25mm 27mm

63 (26.6) 77 (32.5)


52 (21.9)

Additional aortic replacement; n (%) Ascending aorta

98 (41.4)

Aortic hemi-arch

69 (29.1)

Aortic arch

12 (5.1)

Concurrent procedure; n (%) CABG Mitral valve surgery

75 (31.7) 57 (24.1) 14 (5.9)

Valve replacement

5 (2.1)

Valve annuloplasty or repair

9 (3.8)

Tricuspid valve surgery

2 (0.8)

Other cardiac surgery

6 (2.5)

Abbreviation: CABG, coronary artery bypass graft surgery.

Please cite this article in press as: Sherrah AG, et al. Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience. Heart, Lung and Circulation (2015), http://dx.doi.org/10.1016/j.hlc.2015.05.011

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Figure 1 New York Heart Association (NYHA) Heart Failure Class pre-operatively (n=237) and at last followup of survivors (n=207) (p<0.001 for pre- versus postoperative NYHA Class). Figure 3 Kaplan-Meier freedom from re-intervention (aortic valve or coronary artery) up to 10 years following Freestyle aortic bioprosthesis implantation.

Figure 2 Kaplan-Meier freedom from death (from all causes) up to 10 years following Freestyle aortic bioprosthesis implantation.

(n=5), major bleeding (n=2), haemorrhagic CVA (n=1), mesenteric ischaemia (n=1) and sepsis (n=1). No patient undergoing sub-coronary or root inclusion implantation had died by 30 days. In the immediate post-operative period, 49 patients (20.7%) required re-operation for either haemostasis or delayed sternal closure secondary to significant intra-operative bleeding. The incidence of CVA within 30 days of aortic valve surgery was 6.8% (full root n=14, root inclusion n=2). In addition, 5.9% of patients required permanent pacemaker insertion within 30 days of their aortic valve surgery.

Long Term For the entire cohort, freedom from death from any cause was 91.71.9%, 82.83.8% and 56.510.5% at one, five and 10 years, respectively (Figure 2). For patients who had undergone an elective procedure, the freedom from death from any

cause was 94.21.8%, 91.03.0% and 60.813.3% at one, five and 10 years, respectively. During the follow-up period there were 20 late deaths; the causes of late death were pneumonia with sepsis (n=6), cardiac failure (n=7), sepsis (without endocarditis) (n=2), major CVA (n=2), hypoxic arrest (n=1), and an unrelated terminal illness (n=1). The cause of late death was unknown in one patient. Freedom from valvular or coronary artery re-intervention among all patients was 99.50.5%, 91.63.7% and 72.310.5% at one, five and 10 years respectively (Figure 3). In patients who had received the bioprosthesis as a full aortic root replacement (87.8%), freedom from aortic valve or coronary artery re-intervention was 98.61.0%, 94.82.5% and 88.06.9% at one, five and 10 years respectively. During the entire follow-up period, 10 patients (4.2%) required aortic valve or coronary artery re-intervention; in three patients (1.3%) this was due to SVD. In one patient (a 49-year-old male), pseudoaneurysms arose from the left coronary cusp and anterior sinotubular junction of the FSB 15 months following aortic root and ascending aorta replacement; he was managed with redo surgery using a mechanical valved conduit. The other two cases of SVD involved progressive AR in a 43-year-old male, five years following FSB implantation with the root inclusion technique, and progressive AR in a 45-year-old male, seven years following a sub-coronary FSB valve implant (both patients were managed with redo surgery and stented bioprosthesis implantation). Other than SVD, the reasons for re-operation at the aortic valve were endocarditis (n=1) and paravalvular leak (n=1). In 2.1% of patients, re-intervention at the coronary arteries was required (left main coronary artery ostial stenosis requiring CABG in three full root patients, coronary artery disease in a full root patient requiring CABG, and left internal mammary artery disease after

Please cite this article in press as: Sherrah AG, et al. Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience. Heart, Lung and Circulation (2015), http://dx.doi.org/10.1016/j.hlc.2015.05.011

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Figure 4 Average of the mean aortic valve gradients measured post-operatively by annual echocardiography (where available).

concurrent CABG in a sub-coronary patient requiring percutaneous intervention). A total of nine patients (3.8%) suffered prosthetic aortic valve endocarditis during the follow-up period (full root n=8, sub-coronary n=1). For patients who survived beyond 30 days (n=227), at least one post-operative echocardiogram was available in 202 (89.0%). Of these, mean time from surgery to last echocardiogram was 2.32.1 years (range 0.1-10.9 years). There were 92.6% of patients with trivial or no AR at their last echocardiogram. Those with moderate or severe AR included two full root patients (non-operatively managed endocarditis at seven years post-operatively, and described SVD requiring re-operation), two sub-coronary patients (non-structural valve deterioration at six years post-operatively, and described SVD, both requiring re-operation) and one root inclusion (described SVD requiring re-operation). The averages of the available mean gradients across the aortic valve at yearly post-operative time points is shown in Figure 4. At latest follow-up (mean 2.42.3 years), 47 patients (19.8%) took an oral anticoagulant and five of these had suffered a major bleeding event. The total number of patients suffering a major bleeding event was 14 (5.9%). For surviving patients, 97.1% were in either NYHA Class I or II and none were in Class IV at latest follow-up (versus pre-operative NYHA Class, p<0.001) (Figure 1). Pre-operative predictors of mortality at any time postoperatively were: acute aortic dissection (HR 12.8, 95% CI 3.8-43.2; p<0.001), active endocarditis (HR 6.4, 95% CI 1.6-25.5; p=0.01), peripheral vascular disease (HR 4.1, 95% CI 1.4-12.2; p=0.01), congestive heart failure (HR 4.0, 95% CI 1.3-11.8; p=0.01), atrial or ventricular arrhythmia (HR 3.9, 95% CI 1.4-11.0; p=0.01), and chronic airways

limitation (HR 2.6, 95% CI 1.1-6.1; p=0.03). The only preoperative predictor of need for re-intervention was ischaemic heart disease (HR 7.9, 95% CI 1.3-47.2, p=0.02). Age at surgery, implant valve size, method of implantation and extent of aortic surgery were not predictive of need for re-intervention.

Discussion The choice of prosthesis in aortic valve surgery must take into account the lifestyle and predicted lifespan of the individual patient. The ideal valve choice includes identical haemodynamics to a normal aortic valve, acceptable operative mortality and no indication for long-term therapeutic anticoagulation. Additionally, when there is an associated need for replacement of the aortic root and the ascending aorta the alternative valve-conduit combinations need to be considered. This is especially so where cardiopulmonary bypass times can reach several hours and the risk of post-operative morbidity is increased [11,13]. In patients aged 60 to 70 either a mechanical or bioprosthetic valve choice can reasonably be considered and recommended according to current guidelines [14]. A recent large cohort analysis has additionally suggested that bioprostheses may be suitable in patients between the ages 50 to 69 [15], especially in the context of the morbidity associated with long-term therapeutic anticoagulation required with a mechanical prosthesis. Freedom from SVD in a younger patient population following FSB implantation has previously been shown to be acceptable [16]. In a previous larger patient cohort, increasing age was shown to be associated with reduced risk of re-operation [8], but In our cohort of comparatively younger patients, this was not evident. The

Please cite this article in press as: Sherrah AG, et al. Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience. Heart, Lung and Circulation (2015), http://dx.doi.org/10.1016/j.hlc.2015.05.011

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suitability of FSB implantation for patients less than 60 years of age, therefore, cannot be confirmed with our data. Certainly, the limited lifespan of a bioprosthesis increases the risk of morbidity and mortality associated with re-operation. The mortality risk associated with redo aortic root surgery is elevated compared with first-time surgery, but has been shown to be acceptable and may be reduced to <5% in experienced hands [17–19]. As an alternative approach, several reports have demonstrated acceptable clinical outcomes following ‘valve-in-valve’ transcatheter treatment of prosthetic SVD (including following porcine stentless valve surgery) [20,21]. Currently, the transcatheter approach remains reserved for high-risk patients and its suitability in the long term for treatment of prosthetic SVD remains to be seen. The limited durability of glutaraldehyde-treated porcine aortic bioprostheses is typically due to SVD secondary to leaflet calcification resulting in restriction [22]. The FSB is pre-treated with an alpha-amino oleic acid and has shown excellent anti-calcification properties, however it remains at risk of leaflet tearing producing AR [22,23]. Our series reflects this, with all of the cases of SVD (three patients) secondary to AR, and no cases of leaflet restriction. The majority of surviving patients (>90%), however, were free of prosthetic valvular regurgitation with acceptable mean trans-valvular gradients at last follow-up. In our cohort, implanted valve size and implantation technique did not appear predictive of need for re-intervention. Several studies have shown the benefit of stentless valves over stented in the aortic position regarding reduction in transvalvular gradients and left ventricular mass regression [24–27]. A reflected improvement in long-term survival, however, is yet to be definitively demonstrated. Without long-term benefit, many surgeons may be unable to justify the apparent increased cardiopulmonary bypass and crossclamp times required for stentless valve implantation [27]. Surgery necessitated by aortic valve disease alone and the use of the FSB as a sub-coronary implant is also more technically challenging compared with stented prosthesis insertion. This cohort predominantly includes patients receiving the FSB as a full aortic root replacement due to an aneurysmal aorta with or without concurrent aortic valve disease. This is often a requirement where aortopathy exists in association with a bicuspid aortic valve, Marfan syndrome or non-syndromal thoracic aortic aneurysm and dissection. The FSB has previously been shown to be very suitable for such surgical pathology [3,11,28,29] where prosthetic graft extension allows additional replacement of the ascending aorta as well as the aortic arch. Compared with both mechanical and stented composite prosthetic roots, a stentless porcine aortic root has previously shown superior post-operative valvular gradients and ventricular remodelling [30], however, the clinical significance of this is not necessarily certain. The need for coronary artery re-implantation with the full root approach carries some technical challenge and as demonstrated in our cohort, the risk of re-intervention for ostial coronary artery stenosis remains low but present.

The immediate need for re-operation for haemostasis following FSB implantation is inconsistently reported in the literature [7,11] but has been reported as up to 9.5% [13]. This is not unexpected given the extent of additional aortic replacement surgery that may be required and associated coagulopathy that can develop. In our cohort, re-exploration for haemostasis was required in 20.7%, however, this included patients with intra-operatively planned delayed chest closure, a method of reducing post-operative compressive cardiac and haemodynamic compromise in the context of significant coagulopathy. Data describing the use of perioperative blood products was insufficient for inclusion and blood transfusion thresholds were not standardised across included institutions. Our cohort included a single case of pseudoaneurysm development at an FSB implanted as a full root requiring redo surgery at 15 months post-operatively. Although isolated to one occurrence in this series, such post-operative pathology has been noted in prior case reports, and may have an immunoreactive or infective aetiology [31,32]. In larger case series, however, the incidence of this post-operative complication is similarly very low [11,33]. Annual followup of patients who have undergone aortic root surgery is recommended being mindful of this potential complication [34].

Study Limitations Our study has several limitations. The follow-up of all patients to the study end date is incomplete, and the number of patients reaching 10 years of follow-up is few, lending the data to selection bias. Some short-term data, including mean intra-operative blood loss and number of patients transfused, was insufficient and not included in the results. Long-term data was collected retrospectively and may similarly underestimate the number of total adverse events. The study includes multiple surgical implantation techniques (each indicated for differing presenting pathology) and the analysis of their individual outcomes separately is warranted in the future. Although not the aim of the current study, the comparison of the long-term outcomes of patients receiving the FSB with those receiving other aortic valve prostheses at our institutions would additionally be beneficial. Operative approaches and post-operative care was not standardised across the institutions participating in this study; therein variability may lie and potentially produce a confounding factor for our results.

Conclusion Outcomes following implantation of the FSB at our institutions are equivalent to those reported in the large case series from Europe and the USA, both in the short and long term. Acceptable long-term rates of mortality and re-intervention, and echocardiographic parameters, are reported in a cohort receiving the prosthesis predominantly as a full root implant and at a comparatively younger age. For patients with thoracic aortopathy wishing to avoid anticoagulation, the FSB

Please cite this article in press as: Sherrah AG, et al. Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience. Heart, Lung and Circulation (2015), http://dx.doi.org/10.1016/j.hlc.2015.05.011

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may be suitable. Few surgeons at our institutions use the FSB as a sub-coronary implant for isolated aortic valve disease. The durability of this stentless bioprosthesis in younger patients remains to be confirmed given the emerging longterm data and new management strategies available for the redo operation.

Acknowledgements The authors wish to acknowledge the physicians and medical administration personnel who assisted with the collection of patient data. The authors wish to disclose that the first author (AS) receives a research stipend from The Baird Institute, who receive funding from Medtronic Australasia Pty Ltd. There was no involvement from Medtronic in the development or preparation of this manuscript.

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Please cite this article in press as: Sherrah AG, et al. Long Term Outcomes Following Freestyle Stentless Aortic Bioprosthesis Implantation: An Australian Experience. Heart, Lung and Circulation (2015), http://dx.doi.org/10.1016/j.hlc.2015.05.011