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Ann Thorac Surg 1999;67:345-349
© 1999 The Society of Thoracic Surgeons

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Original Articles

Clinical and hemodynamic performance of the freestyle aortic root bioprosthesis

^a Department of Cardiac Surgery, Laval Hospital, Ste-Foy, Quebec, Canada

Address reprint requests to Dr Cartier, Department of Cardiac Surgery, Laval Hospital, 2725 chemin Ste-Foy, Ste-Foy, PQ G1V 4G5, Canada

Presented at the Thirty-fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 26–28, 1998.

	Abstract

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Background. The objective of this study is to assess the clinical and hemodynamic performance of a stentless porcine bioprosthesis, the Freestyle aortic root bioprosthesis.

Methods. Consenting patients requiring isolated aortic valve or aortic root replacement received the Freestyle bioprosthesis. Clinical follow-up and echocardiographic data were obtained at discharge, 3 to 6 months, 1 year, and annually thereafter.

Results. Two hundred seventy-six patients received a Freestyle aortic root bioprosthesis between January 1993 and July 1997. The mean age was 67.7 years. Preoperatively, 86.3% were either New York Heart Association class III or IV. Two hundred thirty-eight patients underwent valve (subcoronary) replacement, 36 underwent aortic root replacement, and 2 underwent valve replacement using the root-inclusion technique. The early mortality was 5.4%, with 3.3% mortality for the subcoronary technique and 19.4% mortality for aortic root replacement. The mean gradient decreased significantly between discharge and the 3- to 6-month follow-up and stabilized thereafter. The effective orifice area increased significantly from discharge to 3 to 6 months’ follow-up. At 3 years, 84.4% of the patients had either no or trivial regurgitation.

Conclusions. The Freestyle bioprosthesis has good clinical performance and good short-term hemodynamic performance. The majority of the regurgitation identified is not clinically significant.

	Introduction

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Aortic valve dysfunction is the most common cause of valve replacement in our cardiac surgical population. An array of valve replacement prostheses are available from which to choose, each with their specific advantages and disadvantages. When replacing a failing valve, the goal should be to restore normal hemodynamic performance while imposing the lowest possible rate of valve-related complications on the patient. These goals need to be balanced against the desire to provide the patient with a valve that is durable enough to avoid reoperation, if possible. To restore hemodynamic function, we need a valve that demonstrates the highest possible ratio of effective orifice area to anatomic area, especially in small sizes [1]. Traditional bioprostheses have a smaller effective orifice area than mechanical prostheses of similar anatomic area. Despite changes in design, there is still concern about high pressure gradients in small valve sizes. Mechanical valves seem to achieve slightly better results in small sizes. However, anticoagulation therapy puts patients of all ages at risk for hemorrhage, and it is preferable to avoid it, if possible, especially in the older age groups.

The outstanding hemodynamic performance of homograft [2] and autograft valves has been one of the factors contributing to their growing popularity. This trend encouraged the valve companies to develop stentless porcine aortic valves. The Medtronic Freestyle aortic root bioprosthesis was approved by the US Food and Drug Administration for human investigational use in July 1992. The Medtronic Freestyle aortic root bioprosthesis is a full porcine aortic root with native porcine coronary ostia intact. The porcine aortic root is preserved in a buffered 0.2% glutaraldehyde solution using a fixation method called "physiologic fixation," which allows zero pressure differential across the leaflets and a pressure of 40 mm Hg across the aortic wall. This method of fixation preserves the natural collagen structure of the leaflets and maintains the native root geometry. The Freestyle valve is treated with a proprietary antimineralization process, alpha-amino oleic acid, synthesized from oleic acid, a naturally occurring fatty acid. A thin polyester cloth covering has been added to strengthen the proximal suture line and cover any exposed porcine myocardium.

	Material and methods

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
This study is a prospective nonrandomized clinical trial of the Freestyle aortic root bioprosthesis. Patients 20 years of age or older requiring aortic valve or aortic root replacement were eligible to participate, including patients undergoing concomitant procedures such as coronary artery bypass grafting or valve reconstruction. Patients requiring concomitant valve replacement or having a preexisting prosthetic valve in another position were excluded from the study. The study was approved by the hospital ethical committee in November 1992.

From January 1993 to July 1997, 281 valves were implanted, with five of the valves explanted during the same operation: three were explanted for unacceptable hemodynamics, one because of occlusion of the right coronary ostia, and one because of a tear between the prosthesis and the anterior leaflet of the mitral valve. All of these explants occurred early in the study and may have been caused in part by the learning curve. Data from the remaining 276 patients were available to complete this study.

There are three techniques commonly used for homograft, autograft, or stentless bioprosthesis implantation: (1) aortic root replacement, (2) root-inclusion (the intraaortic cylinder), and (3) subcoronary technique (valve replacement). At Laval Hospital, 86.2% (238) of the Freestyle implants were performed using the subcoronary technique (with or without scalloping the noncoronary sinus), 13% (36) were aortic root replacements, and there were two root-inclusions.

Patient demographics are summarized in Table 1. Sex distribution was almost equal, and the majority of patients were in New York Heart Association functional class III and IV. The most common risk factor was left ventricular dysfunction (88.8%) with ejection fraction of less than 50% occurring in 25% of patients. It is important to note that 11.2% of the patient population had a preoperative history of cerebrovascular accident or transient ischemic attack.

Sizing is of crucial importance. Undersizing can be a source of dysfunction, and unless a perfectly snug annular fit is obvious, a size larger valve should be implanted. In cases in which the sinotubular junction is found to be more than one valve size larger than the annulus, one should consider alternative implant techniques such as a root-inclusion or a root replacement.

Definitions of morbid prosthesis-related complications are based on the guidelines of The American Association for Thoracic Surgery and The Society of Thoracic Surgeons [3]. Morbidity included structural deterioration, nonstructural dysfunction, thromboembolism, anticoagulant or antiplatelet-related hemorrhage and endocarditis.

Hemodynamic performance of the Freestyle bioprosthesis was assessed by echocardiography. Echocardiographic Doppler assessments were made before discharge, 3 to 6 months after implant, at 1 year, and annually thereafter. Echocardiographic measurements [4] included cardiac output, mean pressure gradient, effective orifice area, and regurgitation.

Continuous data were expressed as mean ± standard deviation. Percentages were determined for categorical variables. Comparisons of mean gradient, effective orifice area, and cardiac output at discharge, 3 to 6 months, 1 year, and 2 years were analyzed using a repeated-measures analysis of variance design with a sphericity test on orthogonal components. This test determines whether or not the F statistic from the univariate procedure is valid. As p values of the F test were significant at the 0.05 level, only repeated measures analyses were performed. Categorical data were analyzed using Fisher’s exact test. Product-limit analyses (also called Kaplan-Meier analyses) were used to report the time-dependent cumulative probabilities of the outcome for complications. Plots of negative logarithms of the survival function versus time revealed that parametric models were not appropriate for survival data. All reported p values are two-tailed and were declared significant at = 0.05. The statistical package program SAS (SAS Institute Inc, Cary, NC) was used to perform the analyses.

	Results

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
Patient follow-up
The total cumulative patient follow-up for the 276 implants was 554.6 patient-years with a mean follow-up of 2.0 patient-years. Although this is a short follow-up, the New York Heart Association class remained stable with 95% of the group in class I or II at the 4-year follow-up. Sinus rhythm was present at each follow-up in almost 90% of the patients. The antithromboembolic therapy of choice was aspirin. Warfarin was reserved for patients in atrial fibrillation or with higher risks of thromboembolism.

Complications
Mortality
Fifteen patients died within 30 days of operation, 8 (5 cardiac, 3 noncardiac) in the subcoronary group and 7 (all cardiac) in the aortic root replacement group. The early mortality for the entire group was 5.4%. It was 3.3% for valve replacement and 19.4% for root replacement. Eighteen patients died during follow-up. There were 13 noncardiac deaths, 2 valve-related deaths, 2 cardiac deaths, and 1 unexplained death. The 2 valve-related deaths were caused by a cerebrovascular accident 3 years postoperatively in 1 patient and renal failure secondary to multiple peripheral emboli 7 months postoperatively in the second patient. Freedom from valve-related death at 4 years was 98.8% ± 0.9%. Freedom from cardiac death at 4 years was 94.8% ± 1.4%. Freedom from noncardiac death at 4 years was 92.7% ± 1.9% and freedom from death of any cause at 4 years was 86% ± 2.4%.

Neurologic and thromboembolic events
There were 40 thromboembolic events of which 33 were neurologic. Fourteen of the events were valve-related and 19 events were non–valve-related. Of the 33 neurologic events, 21 (7.6%) were early events, of which 15 were permanent and 6 were transient. Of the 12 late events, 6 were permanent and 6 transient. The freedom from valve-related neurologic events at 4 years was 96.7% ± 1.2% for permanent and 97.5% ± 1.0% for transient. The freedom from any neurologic events at 4 years was 87.3% ± 2.1%.

Anticoagulant- or antiplatelet-related hemorrhage
There were 8 anticoagulant- or antiplatelet-related hemorrhages, 2 early and 5 late. Five were gastrointestinal tract bleeds, 2 epistaxis, and 1 subdural hematoma. Six of the patients who suffered a hemorrhage were taking warfarin, 2 were taking ASA. Freedom from anticoagulant-related hemorrhage at 4 years was 96.8% ± 1.1%.

Hemolysis
Two patients, both with endocarditis, had hemolysis postoperatively. Freedom from hemolysis at 4 years was 99.1% ± 0.6%.

Prosthesis-related complications
There were no cases of structural valve deterioration. There have been four valve-related reoperations. Two were for endocarditis almost 1 year postoperatively. The third patient was reoperated on 33 days postoperatively for a paravalvular leak, and the fourth patient had a reoperation 4 years postoperatively for progressive central regurgitation caused by aneurysmal dilatation of the native aortic root. This patient underwent a successful root replacement with a homograft. Freedom from reoperation at 4 years was 98.8% ± 0.7%.

Overall, there were 4 cases of endocarditis: 2 were treated surgically (see above) and 2 medically. Freedom from endocarditis at 4 years was 98.3% ± 0.8%. Six patients had a significant paravalvular leak. Included in these 6 patients were the 2 patients with endocarditis who underwent reoperation. A third patient had a paravalvular leak and underwent successful surgical repair of the bioprosthesis. The fourth case that was echocardiographically described as a paravalvular leak was actually a central regurgitation secondary to progressive aortic root enlargement. The last 2 patients are being followed up clinically and have not yet needed reoperation. Freedom from paravalvular leak at 4 years was 97.6% ± 1.05%.

Hemodynamic performance
The most interesting hemodynamic data concerns the mean gradient and the effective orifice area. Although there was no statistical difference between cardiac output at any time during follow-up, there was a statistically significant decrease (p < 0.001) in average mean gradient for all valve sizes from discharge to 3 to 6 months (Fig 1) postoperatively. Similarly, there was a statistically significant increase (p < 0.05) in average effective orifice area from discharge to 3 to 6 months for all valve sizes (Fig 2).

View larger version (22K): [in this window] [in a new window]   Fig 1. Mean systolic gradient at follow-up.

View larger version (19K): [in this window] [in a new window]   Fig 2. Effective orifice area at follow-up.

View larger version (35K): [in this window] [in a new window]   Fig 3. Prosthetic valve regurgitation at follow-up.

	Comment

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

Operative mortality for the Freestyle valve using the subcoronary technique (3.3%) is comparable to that of any conventional aortic valve replacement [6–8]. Five patients died of cardiac causes. Although the operative mortality for root replacement (19.4%) is of more concern, the data are comparable to the Society of Thoracic Surgeon database from Summit Medical. The Society’s database reports that the mortality for aortic root reconstruction is 14.9% for people younger than 70 years and 21.7% for those older. Root replacement in the Freestyle series was performed only on patients with combined aortic valve diseases associated with aortic root diseases.

Seven of the 36 patients who underwent an aortic root replacement died during the operation. All of the deaths occurred in women who were between 56 and 77 years of age (mean, 66 years). Of the 7 deaths, root replacement was deemed necessary because of extensive disease in the ascending aorta in 5 patients, whereas it became necessary in the other 2 patients. Of the 36 root replacements, serious technical difficulties were encountered in 6 patients. Three of the 6 patients encountering technical difficulties died and are included in the 7 operative deaths. Uncontrolled bleeding was the cause of death in 2 cases. A disinsertion of the anterior leaflet of the mitral valve occurred during operation in 2 other patients. In 2 patients, the procedure was performed as a second operation because of valvular dysfunction, and 1 patient could not be weaned from bypass. Although none of the technical difficulties can be attributed as the immediate cause of death, they led to lethal complications.

Although the incidence of early neurologic events was significant (7.6%), it should be noted that preoperative neurologic events in this patient population were also high (11.2%) (Table 2), as was carotid artery disease (5.4%). The incidence of stroke is higher in a prospective study than in a retrospective study and it increases with age, approaching 9% in patients older than 75 years [9, 10]. This could explain these results. Late events occurred less frequently, and the freedom from any valve-related or non–valve-related neurologic events at 4 years was 87.3% ± 2.1%.

In the single reoperation for central regurgitation caused by native aortic root enlargement, the bioprosthesis had been implanted using the subcoronary technique. In retrospect, this patient was not a good candidate for a subcoronary stentless valve. As pointed out by David and associates [11], if the diameter of the sinotubular junction is more than 10% larger than the diameter of the prosthesis, the risk of regurgitation increases because of lack of coaptation of the leaflets. The initial procedure should have been either a root replacement or a root-inclusion using a stentless valve, or implantation with a conventional stented prosthesis.

The hemodynamic performance of the Freestyle bioprosthesis is comparable to that of homografts or autografts [12]. The decrease in mean systolic gradient and the increase in effective orifice area has also been seen with other stentless valves [13] but not with stented prostheses. These changes could be related to septal and ventricular hypertrophy, which may constrict the left ventricular outflow. This dynamic narrowing disappears postoperatively as the myocardial thickness returns toward normal. These hemodynamic changes could also be related to the resolution of hematoma or edema at the anastomosis level early in the postoperative period. A small degree of prosthetic valve regurgitation was thought to be a problem early in the study but subsequent follow-up echocardiography showed that in almost all patients (97%) it was not hemodynamically significant. Regurgitation also appeared to diminish with time (Fig 3). Only longer follow-up will answer these concerns.

The Freestyle aortic root bioprosthesis is very versatile. It can be used for full root or valve replacement. The bioprosthesis can be easily rotated or the noncoronary sinus of Valsalva can be used to enlarge the host aortic root, if necessary. The hemodynamics are comparable to homografts or autografts. The absence of a stent allows the implantation of a larger size prosthesis. This fact must be taken into consideration when comparing hemodynamic results between stentless and stented prostheses. One should compare the results of a given stentless valve size with those of a stented valve that is one to two sizes smaller. Although it may be more technically demanding than a stented valve to implant, any surgeon with experience in aortic valve replacement can master the technique. The lack of a stent and the new antimineralization process (alpha-amino oleic acid) [14] should improve durability. Long-term follow-up will show whether the valve meets its expectations.

	Acknowledgments

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
We thank Louise Côté, Jacinthe Aubé, clinical research nurses, Martine Fleury for secretarial support, and Serge Simard for statistical analysis.

	Footnotes

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 
The authors are consultants for Medtronic.

They are part of a clinical trial on the Freestyle valve and have received financial support to defray research expenses.

	References

Top Footnotes Abstract Introduction Material and methods Results Comment Acknowledgments References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Paul C. Cartier Jacques Métras Denis Desaulniers Michel D. Lemieux Gilles Raymond Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Cartier, P. C. Articles by Raymond, G. Search for Related Content PubMed PubMed Citation Articles by Cartier, P. C. Articles by Raymond, G.