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Ann Thorac Surg 2007;83:2162-2168
© 2007 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Early Clinical and Hemodynamic Outcomes After Stented and Stentless Aortic Valve Replacement: Results From a Randomized Controlled Trial

Ayyaz Ali, MRCSa,*, James C. Halstead, MRCSa, Fay Cafferty, MSa, Linda Sharples, PhDa, Fiona Rose, BAa, Evelyn Lee, FRCPa, Rosemary Rusk, MRCPa, John Dunning, FRCSa, Vincenzo Argano, FRCSb, Steven Tsui, MD, FRCSa

a Department of Cardiothoracic Surgery, Papworth Hospital, Papworth Everard, Cambridge, United Kingdom
b Department of Cardiothoracic Surgery, Morriston Hospital, Swansea, Wales, United Kingdom

Accepted for publication January 12, 2007.

* Address correspondence to Dr Ali, Department of Cardiothoracic Surgery, Papworth Hospital, Papworth Everard, Cambridge, CB3 8RE, United Kingdom. (Email: ayyaz75{at}gmail.com).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Background: Stentless aortic bioprostheses were shown to be hemodynamically superior to earlier generations of stented bioprostheses. Modern stented valve designs have improved hemodynamics. A prospective randomized controlled trial was undertaken to compare stentless versus modern stented valves. Our aim was to determine any differences in early postoperative clinical and hemodynamic outcomes.

Methods: Patients with severe aortic valve stenosis (n = 161) undergoing aortic valve replacement were randomized intraoperatively to receive either the C-E Perimount (Edwards Lifesciences, Irvine, CA) pericardial stented bioprosthesis (n = 81) or the Prima Plus (Edwards Lifesciences) (porcine stentless bioprosthesis (n = 80). Transthoracic echocardiograms were performed at one week and eight weeks postoperatively to assess left ventricular mass (LVM) and transvalvular gradients (TVG).

Results: There were no differences between the two groups in baseline characteristics. Cardiopulmonary bypass and ischemic times were longer in the stentless group. Despite similar native aortic annular diameters, the mean size of the prosthesis used in the stentless group was 2.1 mm (SD = 2.8) larger (p < 0.001). Early (30-day) mortality (stentless 3.7% vs stented 2.5%; p = 0.68) and morbidity was similar between groups. Eight weeks postoperatively, LVM (stentless 199 ± 70 vs stented 204 ± 66 grams; p = 0.32) and TVG decreased in both groups (mean systolic gradient; stentless 10 ± 3 vs stented 10 ± 4 mm Hg; p = 0.54) but there was no significant difference between groups.

Conclusions: Despite longer ischemic times in the stentless group, early postoperative outcomes were similar. Both stented and stentless aortic valve replacement offers excellent hemodynamics and can be achieved with low perioperative mortality.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Stentless aortic bioprostheses were shown in earlier small randomized trials to be hemodynamically superior to conventional stented valves [1–4]. The absence of a sewing ring and stent should provide a larger effective orifice area (EOA) and lower transvalvular gradients postoperatively. This should in turn lead to enhanced regression of left ventricular hypertrophy (LVH). However, evidence from more recent randomized controlled trials comparing the two valve types is beginning to suggest that there may not be important differences in hemodynamic performance between stentless and modern stented aortic bioprostheses [5, 6]. Furthermore, the implantation of a stentless valve is technically more challenging and is generally associated with longer myocardial ischemic and cardiopulmonary bypass times. These may result in an increase in the perioperative morbidity or mortality. We conducted a randomized controlled trial comparing clinical and hemodynamic outcomes after stented and stentless aortic valve replacement (AVR) with two state-of-the-art prostheses. In this setting, we initially sought to identify any important differences in early postoperative mortality and morbidity between patients receiving the two valve types. Furthermore, we measured postoperative transvalvular gradients to identify any early differences in hemodynamic performance between a stented and stentless bioprosthesis.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 Acknowledgments
 References
 
Patient flow through the trial is summarized in Figure 1. The study was carried out at two institutions (Papworth Hospital, Cambridge and Morriston Hospital, Swansea) by three surgeons, all of whom were experienced in the placement of both stented and stentless valves. Ethical approval of the study protocol was obtained from local research ethics committees and all patients gave signed consent.


Figure 1
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  		Fig 1. Trial conduct.

 
Patients were eligible for the study if they were over 65 years of age and required AVR for aortic valve disease, where stenosis was the dominant lesion with a peak aortic transvalvular gradient over 50 mm Hg at transthoracic echocardiography. The need for concomitant coronary artery bypass grafting (CABG) did not preclude patients from entering the trial. Preoperative exclusion criteria were the following: active aortic valve infection, active malignant disease, renal failure requiring dialysis, AVR being performed primarily for aortic valve regurgitation, the requirement of additional cardiac procedures (other than CABG), and emergency operations or previous cardiac surgery. In addition, patients were excluded intraoperatively if the surgeon considered them unsuitable for the implantation of a stentless valve (abnormal coronary anatomy, root calcification, annular diameter >29 mm).

After anesthesia was induced, the chest was opened through a median sternotomy. Cardiopulmonary bypass was established using a 24 Fr ascending aortic cannula and a single two-stage venous cannula. Myocardial protection was achieved with antegrade cold blood cardioplegia infused into the isolated aortic root. A transverse aortotomy was used to access the aortic valve. After excision of the aortic valve and annular debridement, the diameter of the aortic annulus was measured with precalibrated cylindrical sizers. Proprietary valve sizers were also used to determine the optimal sizes of both stented and stentless valves for each patient prior to randomization. Before proceeding, the surgeon had to be satisfied that it was safe to implant either a stented or a stentless valve. Participants were randomized on a 1:1 basis to receive either the Edwards Prima Plus stentless porcine bioprosthesis (Edwards Lifesciences, Irvine, CA) or the Carpentier-Edwards (C-E) Perimount pericardial stented bioprosthesis (Edwards Lifesciences). The trial statistician produced a computer-generated randomization list and allocations were contained in sequentially numbered, sealed envelopes. The group allocation was not revealed to the surgeon until all intraoperative measurements were recorded.

The Prima Plus prosthesis was packaged as a porcine root and was implanted with the full subcoronary technique [7]. The inflow opening of the valve is reinforced with woven polyester cloth. All three valve sinuses of the prosthesis were scalloped to minimize the amount of prosthetic aortic wall and to retain as much native aortic root function and dynamics as possible. The inflow or annular suture line was completed with interrupted 4-0 Ethibond (Ethicon Inc, Somerville, NJ) sutures. The outflow suture line consisted of a continuous 4-0 Prolene (Ethicon) suture, fixing the scalloped edges of the valve to the aortic wall and suspending the commissural posts of the valve in the appropriate position. Stented valves were implanted in a supraannular position with interrupted horizontal mattress 2-0 Ethibond sutures. The aortotomy was closed with a continuous 4-0 Prolene suture. The protocols for removal of air and weaning from cardiopulmonary bypass were identical for both groups. Temporary atrial and ventricular epicardial pacing wires were placed in all patients.

Two-dimensional transthoracic echocardiography was employed to measure transvalvular gradients and left ventricular mass (LVM) preoperatively and at one week and eight weeks postoperatively. Standard apical long and short axis views, together with Doppler flow measurements, were utilized to obtain this information. Postoperative outcomes documented included blood loss, intensive care stay, overall hospital stay, and the frequency of postoperative complications. Twelve-month results will be provided in a future report when trial follow-up is complete.

The main objective of this study was to compare early clinical and hemodynamic outcomes between the stented and the stentless valve groups. The primary outcomes are peak and mean transvalvular gradients and LVM at one and eight weeks. Secondary outcomes are operative characteristics, postoperative complications, and 30-day mortality.

Statistical Methods
For the purpose of calculating sample size, it was assumed that at 12 months the mean (SD) peak gradient, mean systolic gradient, and effective orifice area index (EOAI) in the stented valve group would be 30 mm Hg (6), 15 mm Hg (3.5), and 0.8 cm2/m2 (0.35), respectively. It was anticipated that a reduction of one quarter in peak and mean gradients and an increase of one third in EOAI would be observed in the stentless valve group. No difference in LVM index was expected between the two groups. The required sample size was 130 participants (based on 90% power and 5% significance) and the intention was to recruit 160 to allow for loss to follow-up. Data analysis was by intention-to-treat basis for those patients who had primary outcome measurements at 12 months. Baseline findings, operative characteristics, and outcomes were compared between the two groups using two-sample t tests or Mann-Whitney U tests for continuous variables, and {chi}2 or Fisher exact tests in the case of categoric variables. To compare outcomes, multivariate analysis of variance was used, including valve as a fixed factor and baseline measurement as a covariate. Because there was no loss to follow-up before 30 days postoperatively, 30-day mortality was compared using the Fisher exact test. A 5% p value is termed significant. Exploratory subgroup analyses, according to annular diameter at time of operation, were also performed.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 Acknowledgments
 References
 
Between November 2001 and August 2004, 188 patients were recruited to the study (Fig 1). Three percent (5 of 188) of patients who had been consented were withdrawn preoperatively. Within this group, three patients had a transvalvular gradient lower than 50 mm Hg, one patient had very poor views on the preoperative transthoracic echocardiogram rendering insufficient information for the patient to continue in the trial, and another patient suffered from severe chronic obstructive pulmonary disease and it was felt that participation in the trial was not in his best interest. A further twenty-two (12%) patients were excluded intraoperatively, leaving 161 patients for randomization. Reasons for intraoperative exclusion are listed in Table 1. The most common reason for exclusion was excessive splaying of the sinotubular junction secondary to ascending aortic dilatation. Eighty-one patients were randomized to receive a C-E Perimount stented valve and 80 patients to receive a Prima Plus stentless valve. All patients received the allocated valve and completed the eight-week follow-up assessment.


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  		Table 1 Reasons for Intraoperative Exclusion
 
Baseline characteristics of stentless and stented valve recipients were not significantly different (Table 2). There were no differences in age, symptom status, or body surface area. Preoperative transthoracic echocardiography confirmed that the severity of aortic stenosis was similar between both groups as demonstrated by comparable peak and mean transvalvular gradients and a similarly small effective orifice area (EOA). There was no difference in baseline values of LVM or LVM index (LVMI) between patients receiving a stentless or stented valve. In addition, the number of patients requiring concomitant coronary artery surgery was not significantly different between the two groups (Table 2).


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  		Table 2 Baseline Characteristics
 
Baseline left ventricular function was evaluated by measuring ejection fraction with transthoracic echocardiography (Table 2). Mean ejection fraction was identical for the two groups. There was no significant difference in the mean native aortic annular size, although patients in the stentless group received a significantly larger valve prosthesis (Table 3). Myocardial ischemic and cardiopulmonary bypass times were significantly longer when implanting stentless valves. This observation held true whether or not the patient required concomitant coronary artery bypass grafting (Table 3).


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  		Table 3 Intraoperative Data
 
The 30-day mortality for stentless recipients was 3.7% (3 of 80 patients), for stented recipients it was 2.5% (2 of 81 patients) (p = 0.68). Of the three stentless deaths, one patient died within 24 hours postoperatively from a low cardiac output state related to acute left ventricular failure in the absence of any aortic regurgitation (ischemic time, 101 minutes). The other two patients both developed mediastinal infection, one of whom developed methicillin-resistant Staphylococcal aureus (MRSA) septicemia. These deaths occurred on days 13 and 21, respectively, in the intensive care unit. The MRSA septicemia secondary to prosthetic valve endocarditis was the cause of death in one of the stented-valve recipients on day 26. The other death in the stented group was due to adult respiratory distress syndrome on day 18.

The mean length of stay in the intensive care unit was no different between groups: 22 hours (SD = 5) for stented versus 21 hours (SD = 7) for stentless valve recipients (p = 0.683) nor was overall length of hospital stay; eight days (SD = 6) for stented, eight days (SD = 5) for stentless valve recipients (p = 0.990). There was no important difference between the two groups with regard to postoperative blood loss despite a significantly longer cardiopulmonary bypass run in the stentless group (Table 4). The requirement for resternotomy for exploration of excessive postoperative bleeding was also similar: four (5%) patients in the stented group and five (6%) in the stentless group needed to return to the operating theatre for this reason (Table 4). Approximately 40% of patients in both groups developed atrial fibrillation in the postoperative period. Three percent of patients with either valve type developed a significant sternal wound infection. Only one patient suffered a perioperative myocardial infarction; this patient underwent stentless AVR with concomitant CABG. There were no neurologic complications in our study population in the eight-week follow-up period. Six (8%) patients with a stentless valve and 3 (4%) with a stented valve required implantation of a permanent pacemaker prior to discharge (Table 4). This difference was not statistically significant (p = 0.319).


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  		Table 4 Postoperative Outcomes and Complications
 
Transthoracic echocardiography was used to assess hemodynamic performance and measure LVM (Tables 5 and 6). Go This was performed preoperatively and again at one and eight weeks postoperatively. In both groups there was a large and comparable reduction in the absolute value of peak and mean systolic transvalvular gradients one week after surgery (Table 5). There was a slight further reduction in mean and peak gradients at eight weeks (Table 6). However, at one and eight weeks postoperatively there were no significant differences between the two groups in either peak or mean transvalvular gradients (Fig 2). Similarly, EOA increased in both groups but there was no statistically significant difference between the groups in EOA (Fig 3) or EOAI. The LVM was reduced from baseline although the significance of these measurements so early after valve replacement is questionable. The LVM was seen to regress in both groups with a trend toward greater regression in the stentless group at one week (p = 0.066). At eight weeks postoperatively, LVM was seen to have regressed significantly in both groups; there was no difference in absolute LVM or LVMI at this time point between groups (Fig 4). The overall reduction in LVM from baseline was also not found to be different between groups at eight weeks (Fig 4). At one and eight weeks postoperatively no patient in either group had more than mild aortic regurgitation at transthoracic echocardiography.


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  		Table 5 Hemodynamic Outcomes: One Week
 

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  		Table 6 Hemodynamic Outcomes: Eight Weeks
 

Figure 2
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  		Fig 2. Mean systolic transvalvular gradient (95% confidence intervals). (AVR = aortic valve replacement.)

 

Figure 3
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  		Fig 3. Effective orifice area (95% confidence intervals). (AVR = aortic valve replacement.)

 

Figure 4
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  		Fig 4. Left ventricular (LV) mass (95% confidence intervals). (Significant reduction in LV mass from preoperative to eight weeks in both groups. Stented, p < 0.001; stentless, p < 0.001; AVR = aortic valve replacement.)

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
Acknowledgments
 References
 
Proponents of stentless bioprostheses claim that their design characteristics impart a superior hemodynamic profile in comparison with conventional stented valves [8–11]. Due to the absence of a rigid stent and sewing ring, the stentless valve produces a larger EOA for transvalvular flow. Theoretically, this may result in lower transvalvular gradients with greater unloading of the left ventricle and consequently enhanced LVM regression. The suggestion is that superior LVM regression may correlate with improved long-term survival [12, 13] although this has never been demonstrated in a population with aortic valve disease. It is inferred from observations made in patients with LVH associated with systemic hypertension [14–16], where survival is adversely affected by increasing LVM. Questions of long-term survival and outcome requires long-term patient monitoring and cannot be addressed by this study, which focuses on early outcomes.

The use of a stentless valve is technically more challenging, particularly when inserted with a full subcoronary technique. There are two suture lines rather than one and attention must focus on valve geometry as technical errors in suspending the valve can easily lead to valvular incompetence. The greater technical demand of stentless valve surgery translates into longer cross-clamp and cardiopulmonary bypass times in comparison with stented valve replacement. One of our aims was to determine whether this resulted in greater perioperative mortality or an increased incidence of postoperative complications. We did not observe any differences in 30-day mortality or postoperative morbidity between patients undergoing stented or stentless AVR. The 30-day survival of the stented and stentless valve recipients was excellent at 97.5% and 96.3%, respectively. This compared well with the mortality predicted by the logistic EUROscore of 6.2% for the stented and 6.1% for the stentless valve group. Thus, despite being more difficult to implant, with significantly longer ischemic times, stentless valve surgery can be accomplished with acceptably low mortality and a low incidence of complications. The mean duration of stay in the intensive care unit and overall hospital stay were almost identical to patients who received a stented valve.

Our echocardiographic measurements did not demonstrate any significant differences in postoperative transvalvular gradients. The presence of a sewing ring and stent with modern valve design did not result in higher gradients in stented valve recipients, although there is some evidence that transvalvular gradients continue to decrease with time in patients with a stentless valve due to remodeling of the aortic root [9]. A further report from our trial will address this issue when one-year follow-up is complete. Stentless valves are inherently more physiologic as the normal dynamics of the aortic root are maintained, but despite their closer approximation to normal physiology in the present study they were not associated with improved hemodynamic outcomes early after AVR. It is possible that patients most likely to benefit from the stentless design are those with smaller aortic annuli. The most common measured native aortic annular diameter in both groups was 25 mm. Only 22 of the patients randomized in our study were measured to have an annular diameter of less than 23 mm. Thirteen of these patients received a stented valve, and the remaining nine were implanted with a stentless prosthesis. Notably, the peak transvalvular gradient was higher among stented recipients within this subgroup, although the number of patients in this subgroup was small. Those patients with an annular diameter less than 23 mm receiving a stented valve had a peak gradient of 27 mm Hg, whereas those who underwent stentless valve replacement had only a 16 mm Hg peak gradient. Similarly, the mean transvalvular gradient was 7 mm Hg in stentless recipients within this subgroup, compared with 14 mm Hg in patients with a stented valve. A larger number of patients with small aortic annuli need to be studied to identify whether this is an important observation. In practice this would be difficult to perform in a randomized fashion as this subgroup only accounted for 14% of our total trial patient population.

Earlier trials reported a benefit of stentless prostheses in terms of superior hemodynamic performance and left ventricular mass regression [4]. However, these studies utilized first-generation stented bioprosthetic valves. The excellent performance of more modern stented pericardial prostheses has been well documented and is likely to be responsible for our failure to detect any early differences in hemodynamic performance [17]. Our findings are consistent with other recent randomized controlled trials comparing stentless and modern stented valves, which also failed to identify a difference in early clinical or hemodynamic outcomes in patients undergoing stentless and stented AVR [5, 6].

Early clinical and hemodynamic outcomes after modern stented and stentless aortic valve replacement are similar. Both valves confer excellent hemodynamics with low postoperative morbidity and mortality.


   Acknowledgments
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
References
 
This trial was funded in part by Edwards Lifesciences. We would like to acknowledge the following individuals at Papworth Hospital for their time and dedication to the study: Leigh Clements, superintendent radiographer; Dr Hester Goddard, research officer; Celia Hyde, Sister; Julie Morrison, surgical bookings coordinator; Karen Parker, echocardiography technician; Emer Sonnex, research radiographer; Margaret Williams, medical secretary; Chris Wisbey, head of cardiac technology; Jackie Yates, research and development manager; Sarah Dyas, clinical research assistant; the cardiac support nurses, and the preadmission clinic staff.

Furthermore, we also wish to acknowledge the following individuals at Morriston Hospital: Debbie Hartman, clinical research assistant; Dr Geraint Jenkins, consultant cardiologist; and Alisa Wallis, clinical scientific officer.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. David TE, Bos J, Rakowski A. Aortic valve replacement with the Toronto SPV bioprosthesis J Heart Valve Dis 1992244–8.
  2. Sintek CF, Fletcher AD, Khonari S. Stentless porcine aortic root: valve of choice for the elderly patient with small aortic root? J Thorac Cardiovasc Surg 1995;109:871-876.[Abstract]
  3. Westaby S, Huysmans HA, David TE. Stentless aortic bioprostheses: compelling data from the Second International Symposium Ann Thorac Surg 1998;65:235-240.[Abstract/Free Full Text]
  4. Walther T, Falk V, Langebartels G, Kruger M, et al. Prospectively randomized evaluation of stentless versus conventional biological aortic valves: impact on early regression of left ventricular hypertrophy Circulation 1999;100(suppl 19):II6-II10.[Medline]
  5. Cohen G, Christakis GT, Joyner CD, et al. Are stentless valves hemodynamically superior to stented valves?A prospective randomized trial. Ann Thorac Surg 2002;73:767-768.[Abstract/Free Full Text]
  6. Doss M, Martens S, Wood JP, et al. Performance of stentless versus stented aortic valve bioprostheses in the elderly patient: a prospective randomized trial Eur J Cardiothorac Surg 2003;23:299-304.[Abstract/Free Full Text]
  7. Moreno-Cabral CE, Miller DC, Shumway NE. A simple technique for aortic valve replacement using freehand allografts J Card Surg 1988;3:69-76.[Medline]
  8. Fries R, Wendler O, Schieffer H, Schafers HJ. Comparative rest and exercise hemodynamics of a 23-mm stentless versus 23-mm stented aortic bioprostheses Ann Thorac Surg 2000;69:817-822.[Abstract/Free Full Text]
  9. Del Rizzo DF, Goldman BS, Christakis GT, David TE. Hemodynamic benefits of the Toronto Stentless Valve J Thorac Cardiovasc Surg 1996;112:143-146.
  10. Pibarot P, Dumesnil JG, Jobin J, Cartier P, Honos G, Durand LG. Hemodynamic and physical performance during maximal exercise in patients with an aortic bioprosthetic valve: comparison of stentless versus stented valves Am J Coll Cardiol 1999;34:1609-1617.[Medline]
  11. Casabona R, De Paulis R, Zattera GF, et al. Stentless porcine and pericardial valve in aortic position Ann Thorac Surg 1992;54:681-685.[Abstract/Free Full Text]
  12. Rossi A, Tomaino M, Golia G, Anselmi M, Fuca G, Zardini P. Echocardiographic prediction of clinical outcome in medically treated patients with aortic stenosis Am Heart J 2000;140:766-771.[Medline]
  13. He GW, Grunkemeier GL, Gately HL, Furnary AP, Starr A. Up to thirty year survival after aortic valve replacement in the small aortic root Ann Thorac Surg 1995;59:1056-1062.[Abstract/Free Full Text]
  14. Levy D. Clinical significance of left ventricular hypertrophy: insights from the Framingham Study J Cardiovasc Pharmacol 1991;17(suppl 2):S1-S6.
  15. Ghali JK, Liao Y, Simmons B, Castaner A, Cao G, Cooper RS. The prognostic role of left ventricular hypertrophy in patients with or without coronary artery disease Ann Intern Med 1992;117:831-836.[Medline]
  16. Levy D, Garrison RJ, Savage DD, Kannel WB, Castelli WP. Left ventricular mass and incidence of coronary heart disease in an elderly population cohortThe Framingham Heart Study. Ann Intern Med 1989;110:101-107.[Medline]
  17. Pelletier LC, Carrier M, Leclerc Y, Dyrda I. The Carpentier-Edwards pericardial bioprosthesis: clinical experience with 600 patients Ann Thorac Surg 1995;60(2 suppl):S297-S302.[Medline]



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