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Original Articles: Cardiovascular

Ten-Year Experience With Stentless Aortic Valves: Full-Root Versus Subcoronary Implantation

^a Department of Cardiothoracic Surgery, Heart Institute Lahr/Baden, Lahr
^b Institute of Cardiovascular Medicine of the University Witten-Herdecke, Witten, Germany

Accepted for publication October 2, 2007.

^_* Address correspondence to Dr Florath, Heart Institute Lahr/Baden, Hohbergweg 2, Lahr, D-77933, Germany (Email: ines.florath{at}heart-lahr.com).

Presented at the Forty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 29–31, 2007.

Drs J. Ennker and Florath disclose that they have a financial relationship with Medtronic Inc.

 

	Abstract

Top Abstract Introduction Patients and Methods Results Comment Discussion Acknowledgments References

 
Background: We compared the midterm outcome after aortic valve replacement with the Freestyle stentless bioprosthesis for the full-root or subcoronary implantation technique, while adjusting for patient and disease characteristics by a propensity score.

Methods: Between 1996 and 2005, 1,014 patients underwent aortic valve replacement with the stentless Medtronic Freestyle bioprosthesis, 168 using full-root technique. Based on a saturated propensity score, 148 matched pairs were created. Mean age of the 296 patients was 73 ± 3 years. Mean follow-up time was 32 ± 30 months (maximum, 116 months).

Results: Operative mortality was 4.7% and 2.7% (p = 0.36) in the full-root and subcoronary groups, respectively. Freedom from reoperation, prosthetic valve endocarditis, major bleeding, and thromboembolism after 9 years was 98% ± 1% and 90% ± 7% (p = 0.38), 95% ± 3% and 92% ± 7% (p = 0.76), 72% ± 21% and 98% ± 2% (p = 0.12), and 75% ± 8% and 84% ± 7% (p = 0.28), for full-root and subcoronary groups, respectively. Survival rates after 9 years were 34% ± 24% and 33% ± 11% (p = 0.46), for the full-root and subcoronary groups, respectively. Patients in the full-root group received larger valve sizes (p = 0.03), and the mean transprosthetic gradients at discharge were significantly lower for each valve size. Nevertheless, during follow-up, peak gradients decreased to a greater extent in patients presenting high peak gradients (>36 mm Hg) at discharge.

Conclusions: As risk-adjusted comparison of both implantation techniques did not reveal any differences regarding operative and midterm outcomes, full-root replacement can be liberally performed in patients with small aortic roots, annuloaortic ectasia, or requiring replacement of ascending aorta.

Biologic heart valve prostheses offer the opportunity of avoiding anticoagulation and, therefore, the risk of thromboembolic and hemorrhagic complications. Current indications recommend a bioprosthesis for aortic valve replacement (AVR) in patients of any age who will not take warfarin or who have major medical contraindications to anticoagulation therapy (class I), in patients older than 65 years without risk factors for thromboembolism (class IIa), and in patients younger than 65 years for lifestyle considerations after detailed discussion of the risks of anticoagulation versus the likelihood of a second valve replacement [1].

The Medtronic Freestyle bioprosthesis is an intact porcine root with ligated coronary arteries. Similar to the use of different implant techniques with human tissue valves, the Freestyle aortic root bioprosthesis can be implanted by several surgical techniques: complete or modified subcoronary, root inclusion, and full root. Using human tissue valves, aortic root replacement was associated with a lower incidence of early reoperation, greater effective orifice area, and less prominent aortic regurgitation on Doppler echocardiography [2, 3] in comparison with the subcoronary technique. However, contradictory results exist neglecting the superiority of the root replacement technique with regard to aortic regurgitation [4, 5]. The only comparison of different implantation techniques for porcine stentless bioprostheses reported higher operative mortality and better hemodynamics, functional class, and freedom from regurgitation with full-root in comparison to the subcoronary implantation technique [6]. Which surgical technique to use—subcoronary implantation or aortic root replacement—is still under debate.

The purpose of the present study was to compare early and late outcomes after AVR with stentless valves for the subcoronary versus full-root implantation technique. As the clinical characteristics differ among patients receiving stentless bioprostheses in different implantation techniques, we adjusted for these confounding factors by a propensity score–based matching analysis [7].

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment Discussion Acknowledgments References

 
Between April 1996 and November 2005, 1,014 patients underwent AVR with the stentless biological Medtronic Freestyle prosthesis (Medtronic Inc, Minneapolis, MN), 168 of them in full-root technique. The surgical technique has been previously described [8]. The prosthesis type, surgical technique, and size selection was according to the surgeon’s preference. The surgical strategy for the subcoronary versus full-root technique changed over the years for all surgeons. At the beginning the subcoronary technique was nearly always used. With increased experience we tended to use stentless valve implantation with full-root replacement liberally in smaller annulus or in annuloaortic ectasia. In all patients with dilatation of the ascending aorta greater than 4 cm, we performed the full-root technique in combination with ascending aorta replacement using a vascular Hemashield prosthesis. The full-root technique was not clustered to a limited number of experienced surgeons implanting stentless valves.

Preoperative and intraoperative data were collected on all patients as a part of a national quality assessment trial of cardiothoracic surgery (Quadra; Quality Assurance Data Review Analysis) using standardized protocols of the German Society of Thoracic and Cardiovascular Surgery [9]. Transthoracic echocardiographic control before hospital discharge (within 10 days after AVR) under rest was performed in all patients by experienced cardiologists. Mean transvalvular pressure gradients were calculated by continuous-wave Doppler using the modified Bernoulli equation.

The retrospective study was approved by the ethics committee of the General Medical Council of the state of Baden-Württemberg, Germany. The approval incorporates written informed consent regarding participation in the study and inspection of the echocardiographic data obtained by their family cardiologist.

Follow-Up
Follow-up information was obtained between January and April 2006 by mailed questionnaires and completed by telephone interviews. Follow-up information concerning survival and adverse valve-related events was 99% and 93% complete, respectively. To complete the adverse events of deceased patients, the information from follow-up conducted in 2000, 2001, and 2003 was used. The questionnaire consists of a quality-of-life assessing questionnaire, the Nottingham Health Profile, and general questions concerning further stay in hospital care since valve replacement, New York Heart Association status, postoperative complications, and current symptoms such as arrhythmias, dizziness, and sensory disturbances in limbs and arms.

The Nottingham Health Profile contains 38 subjective statements divided into six sections: energy, pain, emotional reaction, sleep, social isolation, and physical mobility. The number of statements in each section varies from three in the energy section to nine in the emotional reaction section. Scale scores range from 0 to 100 with a lower score indicating a better perceived quality of life [10]. Sixty-eight percent of all survivors (n = 525) responded to the mailed questionnaire, assessing quality of life. Reasons for not responding were need of care (6%, n = 16), too strenuous (14%, n = 38), illness (9%, n = 23), disagreement (5%, n = 11), stay abroad (1%, n = 3), and without reason (willingly answered on the phone; however, did not return the questionnaire, 59%, n = 156).

Statistical Analysis
Statistical analysis was performed using the software package SPSS (SPSS Inc, Chicago, IL). All continuous data were expressed as mean values (±one standard deviation or standard error of the mean) and compared by the Mann-Whitney U test. Dichotomous variables were evaluated by the univariable ² test and Fisher’s exact test. Survival and freedom from valve-related adverse events were estimated by the Kaplan–Meier method and compared by the log-rank test.

To account for imbalances in the distribution of risk factors between patients receiving the Freestyle bioprosthesis in the subcoronary (SC group) or full-root technique (FR group), a saturated propensity score was calculated by logistic regression, including variables presented in Table 1 irrespective of their significance level [11]. Patients of the SC group were then matched one-to-one with the patients of the FR group by the nearest propensity score (maximum difference, <0.05; 90% were <0.01), which was the probability to receive the Freestyle bioprosthesis using the full-root technique, and by the time of the surgery to avoid different follow-up times between the groups. Table 1 shows the preoperative and operative characteristics for all and for matched patients.

	Results

Top Abstract Introduction Patients and Methods Results Comment Discussion Acknowledgments References

Mean follow-up time was 2.6 ± 2.5 years (maximum, 9.4 years) and 2.7 ± 2.5 years (maximum, 9.7 years), respectively, for the SC and FR groups (p = 0.83). Overall survival was 71% ± 33% and 78% ± 29% after 5 years and 33% ± 20% and 34% ± 24% after 9 years, respectively, for the SC and FR groups (p = 0.46) and was compared with men and women of the general German population with the mean age of the study population [12] (Fig 1). Causes of death after 5 years were of a cardiac nature in 4 patients, cancer in 3 patients, stroke in 2 patients, pulmonary embolism in 1 patient with multiple morbidity such as diabetes mellitus and generalized atherosclerotic disease, re-replacement of the bioprosthesis because of prosthetic valve endocarditis in 1 patient, and unknown in 2 patients.

View larger version (28K): [in this window] [in a new window]   Fig 1. Survival curves by implant technique in comparison with the general German population.

View larger version (20K): [in this window] [in a new window]   Fig 2. Scores (mean ± standard error of the mean) for the different sections of the Nottingham Health Profile (NHP) questionnaire for patients who received stentless valves in subcoronary (open bar) or in full root technique (solid bar) in comparison to the scores obtained for men and women of the general German population older than 71 years (left and right hatched bar, respectively).

View larger version (23K): [in this window] [in a new window]   Fig 3. Transvalvular mean pressure gradients (mean ± standard deviation) for each valve size by implant technique (A; subcoronary, white bars; full root, black bars); transvalvular peak gradients at different follow-up times in comparison with the peak gradients at discharge for the subcoronary (B) and full-root techniques (C). The lines between the gradients at follow-up time and at discharge show the amount of increase (solid line) or decrease (dotted line) in the peak gradient by follow-up time.

Valve-Related Morbidity
Actuarial freedom from aortic valve reoperation was 97% ± 15% and 98% ± 14% after 5 years and 90% ± 25% and 98% ± 14% after 9 years for the SC and the FR groups, respectively (Fig 4A). In the observed study population, 6 patients had to be reoperated on within 747 patient-years, with a linearized rate of late reoperations of 0.54%/patient-year. The indications for reoperations and the implant duration are shown in Table 2.

View larger version (27K): [in this window] [in a new window]   Fig 4. Freedom from reoperation (A), freedom from prosthetic valve endocarditis (PVE; B), freedom from major bleeding events (C), and freedom from neurologic events (D). Numbers below the graphs represent patients at risk.

Freedom from major bleeding was 98% ± 12% and 96% ± 18% after 5 years and 98% ± 12% and 72% ± 36% after 9 years for the SC and the FR groups, respectively (Fig 4C), and freedom from neurologic events was 90% ± 20% and 84% ± 27% after 5 years and 84% ± 27% and 75% ± 28% after 9 years for the SC and the FR groups, respectively (Fig 4D). The linearized rates were 0.69%/patient-year and 2.5%/patient-year for bleeding and neurologic events, respectively. Anticoagulation therapy was required in 19% of the patients in the SC group and 23% in the FR group because of generalized atherosclerotic disease and chronic atrial fibrillation occurring postoperatively or during the follow-up time.

	Comment

Top Abstract Introduction Patients and Methods Results Comment Discussion Acknowledgments References

 
In observational, nonrandomized studies characteristics differ among patients belonging to the different groups of comparison as a result of clinically motivated patient selection or chance. These different patient characteristics may affect different outcomes between groups of comparison besides the variable of comparison, ie, the treatment or, in the present study, the implantation technique [7]. To balance or adjust these effects, a propensity score was proposed by Rosenbaum and Rubin [11].

After adjustment for different patient characteristics by such a propensity score–based analysis, no significantly increased operative mortality was observed for the full-root implantation technique and also no difference was found for midterm survival, midterm valve-related morbidity, and quality of life between different implantation techniques either. Survival and quality of life after AVR with stentless bioprostheses were similar to the age- and gender-matched general German population.

In Table 3, the linearized rates of late adverse events observed in this study are presented and compared with previous studies of several different aortic valve prostheses. In comparison to mechanical aortic valve prostheses, the Freestyle valve had only slightly increased rates for prosthetic valve endocarditis and reoperation and, as expected, quite lower bleeding rates (Table 3) [14, 15]. The rates in the present study were quite similar to the results reported for other bioprostheses, stented or stentless (Table 3) [16, 17], whereas the studies conducted with stentless valves such as CryoLife-O’Brien [18] and Toronto SPV [19] found lower thromboembolic rates (Table 3). However, the complication rates primarily depend on patient-related factors [20]. Comparing the outcome of different studies is quite difficult because of the different baseline characteristics. For instance, the prevalence of risk factors for stroke such as diabetes mellitus, hypertension, atrial fibrillation, left ventricular hypertrophy, and cardiovascular disease may differ in different studies. The prevalence of diabetes mellitus and atrial fibrillation in our study population was twice as high, and the prevalence of hypertension was much higher (70% versus 46% and 38%) than reported for the populations receiving the Toronto SPV [19].

However, persistence of higher velocity ratios for a period of 1 year and less complete left ventricular mass regression in 20% of the population were reported. These patients had mean gradients of 20 mm Hg at discharge, were more often women, and had both lower body surface area and smaller valve sizes [23]. Similar results were obtained from studying velocity ratios (peak velocity through the aortic valve to the peak velocity proximal to the valve) rather than transvalvular velocities, to adjust for variations in systolic performance and cardiac output [22, 24].

The clinical implications of these findings and the optimal surgical management still remain controversial. It has already been postulated that the interaction of aortic root anatomy and surgical experience in subcoronary technique is a major determinant of the performance of the Freestyle valve [22, 25]. Thus, it may be possible that in individual cases suboptimal implantation resulting in distortion of the valve or bulking of valve tissue into the outflow tract may be involved in the evolution of higher gradients. In our study, the transvalvular gradients were even higher than reported previously, which may be partly explained by the more frequent use of the subcoronary technique in patients with small aortic roots than in other series. In this context, it is noteworthy that in our series we observed no moderate or severe aortic regurgitation. Only low or trivial aortic regurgitation was observed in the subcoronary technique, but rarely in the full-root group, a finding that was already made in human tissue valves [2, 4] and in porcine stentless valves [16]. Interestingly, in other series a moderate aortic insufficiency was described in a considerable number of patients after subcoronary implantation, but here the gradients were lower [16]. It may be possible that in these series undersizing was more common, whereas in our series, especially at the beginning of our experience, we tended to oversize the valve in the subcoronary technique. Because with oversizing of the valve the risk for higher transvalvular gradients clearly increases, we now strictly avoid this strategy.

However, despite these new strategies and increasing experience with the subcoronary technique, a risk of higher gradients using the subcoronary technique remains, which can be avoided using the full-root technique. According to our results, the full-root technique can be applied without any significant increase in operative mortality or morbidity. Similar findings were made by Kunihara and colleagues [26] when stentless valve replacement in the full-root technique was compared with conventional stented valve implantation. Many surgeons are reluctant to perform the full-root technique routinely owing to the known difficulties of this technique as well as the fear of bleeding and coronary complications, especially in the elderly [6]. Nevertheless, with proper training and development of routines, this technique is safe and reproducible and can also be liberally used in the elderly. We perform the full-root technique in patients with small aortic roots, in cases of annuloaortic ectasia and replacement of ascending aorta, and in cases in which a prosthesis-patient mismatch would be expected.

A drawback of the full-root implantation technique is the demanding surgery in the case of re-replacement of the aortic valve as a result of prosthetic valve endocarditis or structural valve deterioration. Excellent midterm freedom from reoperation because of structural valve deterioration was reported with approximately 95% at 10 years [16, 27]. Long-term studies showed similar results with stented bioprostheses, whereas the reoperation rate increased more profoundly after 10 to 15 years, especially for patients younger than 60 years [17, 28]. As the maximum follow-up time in the most recent studies of stentless valves is 10 years, no recommendation concerning full-root replacement with stentless bioprosthesis can be given at the moment for younger patients.

The present study is a retrospective observational assessment of outcomes obtained by mailed questionnaires and telephone contacts with the patients and their cardiologists. The response rate to the questionnaire was 68% of all survivors. As a consequence, the quality of life may be overestimated as responders judge their own health and their activity better than the nonresponders [29]. Nevertheless, the response rate of the compared study assessing quality of life in the general German population was similar (69%) [13].

Only limited echocardiographic data were available at the follow-up time as the follow-up visits were performed by the local cardiologists, and echocardiographic examinations are indicated only in the case of changes of the clinical status. Eighty-five percent of the responders signed the informed consent for contacting their cardiologist to obtain their echocardiograms. As most of the patients (66%) underwent valve replacement during the last 5 years, in most of them an echocardiographic examination was still not performed.

	Discussion

Top Abstract Introduction Patients and Methods Results Comment Discussion Acknowledgments References

 
DR OCTAVIO E. PAJARO (Jacksonville, FL): Early on in this study, what was the basis to make the decision whether to use a subcoronary technique or the full-root replacement?

DR J. ENNKER: Well, we learned that in the early days mortality for the full-root procedure was substantially higher, up to 10%. And if you have, for example, an 84-year-old lady on steroids for COPD (chronic obstructive pulmonary disease), she has a substantially enlarged risk for perioperative mortality when replacing the full root. And you may note that we did not use this again, stented valves, also in the aged population. So this was our concern. And the literature is up to 10%. And I know even other reports where they are worse.

DR JOSEPH E. BAVARIA (Philadelphia, PA): That is a beautiful series. I just wanted to know whether you have the data on structural valve deterioration and AI (aortic insufficiency) formation and some of the other hemodynamic determinants for full-root replacement in patients less than age 60? Is the prosthesis, in your experience, deteriorating a littler faster in this age group? What is your opinion?

DR J. ENNKER: This experience is too young. We have been doing so during the last 3 to 4 years, and I have to wait. We had no redo. We will give a presentation at the German meeting in 2 weeks. And together with Professor Lass from Bad Bevensen, we have 250 patients younger than 64. I will send you the presentation.

DR MICHAEL BORGER (Leipzig, Germany): Excellent presentation. You are one of many groups now showing that the Freestyle has very good long-term results.

You stated that you did not put in any stented valves last year. Do you think there is any benefit for a patient who has a relatively large aortic annulus, not so large that they require a total root replacement, but somebody who has a 32-mm aortic annulus and you can easily insert a 27 or a 29 stented valve with a shorter ischemic time? Is there any benefit for this type of patient to insert a stentless valve?

DR J. ENNKER: Well, that is a matter of philosophy. And once we were convinced that this is a better valve, I stuck to this. But I do not argue if you implant a stented valve in a 25 or 27 root. This is all too possible, no doubt.

DR MICHAEL E. JESSEN (Dallas, TX): You showed interesting data that the quality-of-life measures were better with the full root and that the gradients were lower. Do you have any information on LV (left ventricular) mass regression or heart failure class in these patients afterwards? Were they similar, or were they better with the full root?

DR J. ENNKER: Well, the lesser gradient is a better result you can expect for regression of the left ventricular mass. However, there are reports in the literature that after 1 year there is no difference. But anyway, the patients definitely would benefit in the long run.

	Acknowledgments

Top Abstract Introduction Patients and Methods Results Comment Discussion Acknowledgments References

 
The study was supported by Medtronic Inc, Düsseldorf, Germany. We thank Marcella Schabel for assistance with data collection.

	References

Top Abstract Introduction Patients and Methods Results Comment Discussion 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): Juergen A.C. Ennker Alexander A. Albert Ulrich P. Rosendahl Ina C. Ennker Fatmir Dalladaku Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ennker, J. A.C. Articles by Florath, I. Search for Related Content PubMed PubMed Citation Articles by Ennker, J. A.C. Articles by Florath, I. Related Collections Valve disease