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Three Part Question

In [patients undergoing a bioprosthetic aortic valve replacement] is [a stented or a stentless valve] superior [for achieving left ventricular recovery].

Clinical Scenario

You are at a national conference hearing about the benefits of a stentless aortic valve over a conventional stented valve. An eminent speaker from the floor then stands up and contends that there have been no definitively proven benefits for stentless valves. He continues to say that as the implantation time in these older patients is significantly higher with an associated increase in morbidity, that those who implant stentless valves outside of a clinical trial are similar to cardiologists who implant coronary stents outside of published national guidelines, and both practises should be discontinued. You resolve to check the literature yourself.

Search Strategy

Medline 1950 to May 2007 using OVID interface
[aortic valve replacement.mp OR exp aortic valve/] AND [Stentless.mp OR Stented.mp].

Search Outcome

Five-hundred and fifteen papers were found using the reported search. From these, 15 papers were identified and a meta-analysis was additionally found that provided the best evidence to answer the question.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Kunadian et al, 2007 USA	Ten studies were identified that included 919 patients in which the Freedom (Sorin Biomedica Cardio, Via Crescentino, Italy), Freestyle (Medtronic, Minneapolis, MN), Prima Plus (Edwards Life Sciences, Irvine, CA) and the Toronto and Biocor (St Jude Medical, St. Paul, MN) valves were used	Meta analysis (level 1a)	Peak gradient postoperatively	Stentless valve mean difference 5.80mmHg (4.69 to 6.90) better than stented valves	This meta-analysis showed that stentless aortic valves provide an improved level of left ventricular mass regression at 6 months, reduced aortic gradients, and an improved effective orifice area index, at the expense of times that were 23 minutes longer for cross clamp and a 29 minutes longer for bypass. this improvement disappeared after 12 months
			Left ventricular mass Index	At 6 months Weighted mean difference; 6.42, [95% CI 1.21 to 11.63] in favour of stentless valve 12 months WMD, 1.19; [95% CI, - 4.15 to 6.53], no significant difference
			Cross clamp time	Cross clamp time 23 min longer
			Bypass time	Bypass time 29 mins longer
Ali et al, 2006 UK	Patients with severe aortic valve stenosis (n=161) undergoing aortic valve replacement (AVR) were randomised Intraoperatively to receive either the C-E Perimount stented bioprosthesis (n=81) or the Prima Plus stentless bioprosthesis (n =80).	PRCT (level 2b)	Left ventricular mass regression Transvalvular gradients were measured postoperatively	. Haemodynamic performance of the 2 valves was similar with no difference in mean and peak systolic transvalvular gradients 1 year after surgery. In patients with reduced ventricular function (left ventricular ejection fraction [LVEF] <60%), there was a significantly greater improvement in LVEF from baseline to 1 year in stentless valve recipient	There was no difference between groups with regard to age, symptom status, need for concomitant coronary artery bypass surgery, or baseline LVM regression in both groups but with no significant difference between groups at 1 year
Perez de Arenaza et al, 2005 UK	Patients undergoing AVR with an aortic annulus < or =25 mm in diameter were randomly allocated to a stentless (n=93) or a stented supra-annular (n=97) valve	PRCT (level 2b)	change in left ventricular mass (LVMI) measured Measurements were taken before valve replacement and at 6 and 12 month	-LVMI between the stentless versus stented groups at baseline (176+/-62 and 182+/-63 g/m2, respectively) or at 6 months (142+/-49 and 131+/-45 g/m2 respectively . Changes in -reduction in peak aortic velocity (P<0.001) and a greater increase in indexed effective orifice area. (P<0.001) in the stentless group than in the stented group.	Despite significant differences in indexed effective orifice area and peak flow velocity in favour of the stentless valve, there were similar reductions in left ventricular mass at 6 months with both stented and stentless valves, which persisted at 12 months
Bakhtiary et al, 2006 UK	A total of 24 patients (73 +/- 6 years) referred for treatment of aortic stenosis were randomised to aortic valve replacement with stented (Medtronic Mosaic; (Medtronic Inc, Minneapolis, Minn) or stentless (Medtronic Freestyle; Medtronic Inc)	PRCT (level 2b)	Coronary flow was measured preoperatively, 5 days after the operation and 6 months quantify transvalvular gradients left ventricular mass regression	flow increased in both groups significantly (P < .001). This increase was higher in the stentless group compared with that seen in the stented group (343 +/- 137 vs 221 +/- 66 mL/min) Also, coronary flow reserve was higher for stentless valves (3.4 +/- 0.3 for stentless valves and 2.3 +/- 0.1 for stented valves) Mean pressure gradients for Freestyle valves were lower (10 +/- 4 and 8 +/- 3 mm Hg, respectively,vs 19 +/- 6 postoperatively and 15+/- 4 mm Hg at follow-up for Mosaic valves, P < .05).	Normalisation of coronary artery flow after aortic valve replacement for aortic stenosis was more pronounced for stentless valves. This increase was higher in the stentless group compared with that seen in the stented group Left ventricular mass regression was similar in both groups
Totaro et al, 2005 UK	Sixty-three patients (>70 years old) were enrolled. Randomized to the Carpentier-Edwards PERIMOUNT-Edwards Prima Plus Furthermore the best size suitable of the Carpentier-Edwards PERIMOUNT -Magna and the Carpentier- Edwards PERIMOUNT	PRCT (level 2b)	Early postoperative haemodynamic performance	Magna, , was superior to those of both the Edwards Prima Plus and the Carpentier-Edwards PERIMOUNT in both effective orifice area index (1.07 +/- 0.4 cm2/m2, 0.87 +/- 0.3 cm2/m2, and 0.80 +/- 0.2 cm2/m2, respectively) and mean peak gradient (20 +/- 6 mm Hg, 27 +/- 8 mm Hg, and 28 +/- 12 mm Hg, respectively) The best size suitable of Edwards Prima Plus (24.3 +/- 1.7 mm) was significantly superior to those of both the Carpentier-Edwards PERIMOUNT Magna (23.4 +/- 2.1mm) and Carpentier-Edwards PERIMOUNT (22.4 +/- 1.8 mm).	The third-generation stented bioprosthesis Carpentier- Edwards PERIMOUNT Magna had similar function to the stentless valve
Doss et al, 2003 Canada	Forty patients with aortic stenoses, over the age of 75 years, were randomised to receive either the stented Perimount (n=20) or the stentless Prima Plus (n=20) bioprosthesis	PRCT (level 2b)	Left ventricular mass regression, effective orifice area, ejection fraction and mean gradients were evaluated at discharge, 6 months and 1 year after surgery	A significant decrease in left ventricular mass was found 1 year postoperatively However, there was no significant difference in the rate of left ventricular mass regression between the groups	1 year postoperatively, the haemodynamic performance of the valves and the change in the ejection fraction did not differ between the groups
Cohen et al, 2002 Germany	Fifty-three patients were randomised to receive the stented C-E pericardial valve (CE) and 46 patients the Toronto Stentless Porcine valve (SPV). Annuli were sized for the optimal insertion of both valve types, such that surgeons were required to commit to specific valve sizes before randomisation. Echocardiographic measurements and functional status (Duke Activity Status Index) were assessed at 3 and 12 months postoperatively.	PRCT (level 2b)	cardiopulmonary-aortic cross-clamp times perioperative morbidity and mortality implantation effective orifice area - transvalvular gradients regression of left ventricular mass Duke Activity Status Index scores of functional status	Cardiopulmonary bypass times (CE: 118.6+/-36.3 minutes; SPV: 148.5+/-30.9 minutes; p = 0.0001) and aortic cross-clamp times (CE: 95.4+/-28.6 minutes; SPV:123.6+/-24.1 minutes; p = 0.0001). ventricular outflow tract diameter after valvular implantation: SPV: 3.4+/-1.11 mm versus CE: 3.7+/-1.33 mm; p = 0.25). -the actual mean valve size based on internal valvular diameter was no different between groups (CE: 21.9+/-2.0 mm; SPV: 22.3+/-2.0 mm; p = 0.286).	Although offering excellent outcomes, stentless valves did not demonstrate superior haemodynamic indices in comparison to stented valves up to 12 months after. Neither valve offered a superior internal diameter for any given annular diameter
Maselli et al, 1999 Italy	Four groups of 10 patients each were randomly assigned to receive: (1) aortic homograft preserved in antibiotic solution at 4 degrees C, (2) Toronto stentless porcine valve, (3) Medtronic Freestyle stentless valve, or (4) Medtronic Intact aortic valve	PRCT (level 2b)	The left ventricular mass index, effective orifice area index, and peak and mean transaortic gradients were measured by doppler echocardiography before the operation and 8 months postoperatively	The haemodynamic performance indices were much better for the homograft and stentless valves than for the stented one. The absolute left ventricular mass index reduction was greater in the homograft group compared with the Intact (p = 0.0004) and Toronto (p = 0.007) groups. The extent of left ventricular mass index reduction was greater only in the homograft group versus Intact group (p = 0.005).	Multivariate analysis showed that the only predictors of left ventricular mass index reduction were the homograft type, a higher valve size index, and a higher preoperative left ventricular mass index
Bleiziffer et al, 2005 Germany	Twenty patients underwent AVR for aortic stenosis with the St. Jude Medical (SJM) Toronto Root stentless porcine bioprosthesis, using a subcoronary implantation technique. Through the authors' institutional database, 20 additional patients were identified who had undergone AVR with the Medtronic Mosaic stented completely supra-annular porcine bioprosthesis. The patient groups were not matched for labeled valve size, but for annulus diameter measured intraoperatively using Hegar's dilators	PRCT (level 2b)	Hemodynamic performance	Transvalvular mean pressure gradients (MPG) at rest were significantly lower in the stentless group, but cardiac output was similar in both groups. Stress echocardiography also revealed significantly lower gradients at 25 W and 50 W exercise in the stentless group. The EOA index (EOAI), grouped by annulus diameter, tended to be larger in the stentless group and showed no severe patient-prosthesis mismatch (PPM; EOAI <0.65 cm2/m2) which, in contrast, occurred in three patients (15%) in the stented group (p = 0.072).	In summary, the SJM Toronto Root porcine stentless bioprosthesis in the subcoronary position showed lower MPGs and larger EOAs at rest and during exercise compared to the Medtronic Mosaic porcine stented bioprosthesis. Therefore, physically active patients in particular may benefit from use of the stentless valve. Because of its larger EOA, a stentless valve should be implanted if severe PPM is expected.
Borger et al, 2005 Canada	(n = 737). Patients were divided into two groups according to type of bioprosthetic implanted: stentless patients (total n = 310) (Toronto SPV [St Jude Medical, St Paul, MN], n = 146 and Freestyle [Medtronic, Minneapolis, MN], n = 164) and stented patients (total n = 427) (Perimount [Edwards Life Sciences Inc, Irvine, CA], n = 291 and Mosaic [Medtronic], n = 136)	Retrospective study (level 2b)	Midterm LVM regression,	Stentless patients had significantly lower LVM index during follow-up (100 +/- 32 vs 107 +/- 32 g/m2, p = 0.005) and stentless valves were an independent predictor of LVM regression Furthermore, a higher proportion of stented patients had residual LV hypertrophy during follow-up (28% vs 18%, p = 0.001).	Stentless valves were associated with improved midterm survival by univariate analysis, but not by multivariable analysis
			Hemodynamic data,	Predischarge echos revealed that stentless patients had significantly lower mean transvalvular gradients (11 +/- 5 vs 15 +/- 6 mm Hg, p < 0.001) and larger effective orifice areas (1.32 +/- 0.52 vs 1.22 +/- 0.48 cm2, p = 0.01).
			Survival	Follow-up echocardiograms were obtained in 99% of surviving patients 28 +/- 22 (range, 0-79) months postoperatively
	160 consecutive patients on 1 surgeon's list randomized to receive either a Toronto stentless porcine valve (St Jude Medical, Inc, St Paul, Minn) or a Perimount stented bovine pericardial valve (Edwards Lifesciences, Irvine, Calif). Echocardiography was performed at discharge, between 3 and 6 months, and at 1 year after surgery. implanted. stentless biological valves chosen for comparison in the early postoperative period or in preliminary follow-up.	Randomised study (level 2b)	Effective orifice area	At 3 to 6 months for the Toronto versus the Perimount valve, the effectiveorifice area was 1.58 versus 1.66 cm2,	There were no significant differences in hemodynamic function or clinical events between the stented and stentless up to 5 years
			The mean pressure difference	- the mean pressure difference was 7.54 versus 7.42 mm Hg, and the peak velocity was 2.07 versus 2.0.1 m/s
			regression of left ventricular hypertrophy	There was no difference in regression of left ventricular hypertrophy
			Mortality and complications	There was no difference in mortality, or complications other than paraprosthetic regurgitation at 12 months or on follow-up for a proportion of the sample to 8 years
			Regurgitation through the valves	The incidence of regurgitation through the valves was similar for Toronto (10%) and Perimount (13.8%) at 1 year, but mild paraprosthetic regurgitation was found in 5 patients with the Perimount valve and none with Toronto valves
Walther et al, 1999 Germany	180 patients were prospectively selected; 106 patients received a stentless aortic valve (SAV), and 74 received a conventional stented bioprosthesis (CSB). Of these patients, 95% and 96%, respectively, had aortic stenosis. Their mean age was 72.3 and 74.8 years,	PRCT (level 2b)	All patients were in NYHA class 1 or 2 Baseline enddiastolic Left ventricular posterior wall Left ventricular mass index	At follow-up, all patients were in class 1 or 2.Baseline enddiastolic left ventricular posterior wall thickness was 15.6 (SAV) and 14.8(CSB) mm (P=NS) and decreased to 11.8 (SAV) and 13.2 (CSB) mm (P<0.05) at 6 months. Left ventricular mass index was 213 and 202 g/m2 at baseline (P=NS), whereas after 6 months, it was 141 (SAV) and 170 (CSB) g/m2 (P<0.05)	Aortic annulus diameter indexes were comparable at 13.46 (SAV) versus 13.55 (CSB) mm (P=NS). Larger SAVs were implanted because of the oversizing technique. Inhospital mortality (n=3 and 1 for SAV and CSB) was not valve related
Williams et al, 1999 UK	Forty patients were randomised after the annular and sinotubular diameters had been measured St Jude Toronto valve, versus Carpentier-Edwards Perimount valve.	PRCT (level 2b)	Early haemodynamic measurements were made with a thermo dilution cardiac output catheter, and echocardiography was used thereafter Regression of left ventricular mass assessed using magnetic resonance imaging (MRI) at 1 week, 6 months, and 32 months.	Echocardiography showed superior transvalvular gradients in the stentless group at 1 week (mean 5.5+/-3.1 mm Hg cf. 8.9+/-2.5 mm Hg), and this difference was maintained at a mean follow-up time of 32 months (3.5+/-0.6 mm Hg cf. 6.3+/-0.6 mm Hg). Similar regression of left ventricular mass was seen in both groups at 6 months, but at 32 months, measurement in diastole showed a reduction of 38% (P<.01) in the stentless group compared with 20% (P = ns) in the stented group, and measurements in systole showed a 23% (P<.01) and 13% (P = ns) reduction, respectively	The mean annular size was 25.3+/-2.2 mm (CE) and 25.5+/-1.5 mm (Toronto), although it was possible to implant valves with a mean diameter 3 mm larger in the stentless group (26.0+/-1.7 mm cf. 23.0+/-1.7 mm). Haemodynamic performance in the first 24 hours showed no significant difference
Santini et al, 1998 Italy	77 patients (28 men) were prospectively randomised to undergo aortic valve replacement using the Hancock valves (group A: 40 patients, 16 men; age, 77+/-3 years; body surface area, 1.7+/-0.17 m2) or a stentless bioprosthesis (group B: 37 patients, 12 men; age, 76+/-2 years; body surface area, 1.7+/-0.15 m2; Biocor, 17; Toronto SPV, 20 )	PRCT (level 2b)	Bypass time and aortic cross-clamp time Valve size normalised to body surface concomitant myocardial revascularisation neurologic event Actuarial survival at 12 and 24 months peak transaortic gradient regression of left ventricular mass	Bypass time was 123+/-46 versus 133+/-51 minutes, and aortic crossclamp time was 83+/-26 versus 95+/-24 minutes for group A and group B, respectively (not significant) body surface area was 13.7+/-1.5 versus 14.1+/-1.6 mm/m2 for group A and group B Overall perioperative mortality was 5% ingroup A (low patients), and 8% in group B (low cardiac output in 1; major neurologic event in 2 cardiac output in 2)	Actuarial survival at 12 and 24 months is 92% versus 91% and 92% versus 81% for group A and group B, respectively. At 6 months, patients in group A showed a peak transaortic gradient of 25+/-7 versus 20+/-9 mm Hg in group B. Progressive regression of left ventricular mass expressed as a percentage of preoperative value was 10.5% and 19% for group A and group B at 1 year postoperatively (not significant)
Bove et al, 2006 Belgium	145 patients with a Toronto stentless prosthesis are compared with 110 patients with a stented Carpentier-Edwards valve	Retrospective study (level 2b)	The 5- to 10-year clinical outcome transprosthetic gradients - early and late (LVM) regression	survival at 5 years is 82% after stentless AVR versus 68% after stented AVR (p < 0.001) in elderly patients. However, there was no difference in survival at 8 years, being 55.9% and 59.5%, respectively. Stented and stentless xenografts were equally effective in terms of transprosthetic gradients and LVMI regression. mass regression. However, late LV remodeling was predominantly affected by systemic hypertension and severe preoperative LV hypertrophy, resulting in the incomplete LVMI resolution in 61.3% and 66.7% of these patients, respectively	In elderly patients, aortic valve replacement appears to be equally effective with a stentless or stented bioprosthesis
Tsialtas et al, 2007 Italy	The effects of the bioprotheses were studied by echocardiography in 68 patients (age, 74 +/- 7 years)	PRCT (level 2b)	Left ventricular mass	A progressive and similar decrease in left ventricular mass of 30% was observed in both stented and stentless bioprostheses at 12 months	Advantages consisting of a progressive increase in transprosthetic effective orifice area and a decrease of the transprosthetic pressure gradient were observed in the Toronto group in comparison to the CEP and Shelhigh groups the early- and mid-term (12 months) periods after surgery with all 3 types of bioprostheses
			Transprosthetic effective orifice area	A progressive increase in transprosthetic effective orifice area and a decrease in transprothetic pressure gradient were observed at 3, 6, and 12 months in the Toronto group, but these variables showed improvement only at 3 months in the CEP and Shelhigh

Comment(s)

Kunadian et al. in 2007 performed a meta-analysis of all the randomised controlled trials that we identified. They found that the effective orifice area and the mean and peak aortic valve gradients were significantly superior to the conventional stented valves used as controls across the ten studies. In addition, they showed that at six months the left ventricular mass index reduced significantly more in the stentless valve group. However, by 12 months the patients in the stented valve groups had caught up with the stentless valve groups in terms of mass regression and there was no longer a significant difference. No mortality or symptomatic benefits were demonstrated. They also aggregated the times taken to perform the two types of operation. Overall there was a mean increase in the cross-clamp time of 23 min and a 29-min increase in the bypass time. However, Chamber et al. in a randomised, prospective series of 160 stentless and stented biological replacement aortic valves on one surgeon's list, showed that at 3–6 months there was no difference in mortality, regression of left ventricular hypertrophy, complications, or on follow-up for a proportion of the sample to eight years; the same result achieved by Bove et al. in there follow-up for eight years. On the other hand, Borger et al. compared mid-term left ventricular mass (LVM) regression, haemodynamic data, and survival in a large number of patients had tissue aortic valve replacement (n=737). Mid-term follow-up reveals that stentless bioprostheses are haemodynamically superior to stented valves. Ali et al. showed that both stented and stentless bioprostheses are associated with excellent clinical and haemodynamic outcomes one year after AVR. Comparable haemodynamic and LVM regression can be achieved using a second-generation stented pericardial bioprosthesis. Perez et al. studied left ventricular mass index (LVMI) measured by transthoracic echocardiography and, in a subset, cardiovascular magnetic resonance (MR) measurements were taken before valve replacement and at 6 and 12 months. There was a greater reduction in peak aortic velocity (P<0.001) and a greater increase in indexed effective orifice area (P<0.001) in the stentless group than in the stented group. There were no differences in clinical outcomes between the two valve groups after one year. Bakhtiary et al. compared coronary perfusion after aortic valve replacement with stented or stentless porcine bioprosthesis. Coronary flow increased in both groups significantly (P<0.001) after aortic valve replacement. Left ventricular mass regression was similar in both groups. Totaro et al. and Santini et al. targeted old patients (>70 years old) and found that the improved design of the recently introduced third-generation stented bioprosthesis allows implantation of a significantly bigger valve than with the old generation which was similar in function to a stentless valve. On the other hand, Doss et al. found that previously reported findings, faster and more complete regression of left ventricular mass and haemodynamic benefits of stentless valves were not reproducible. Cohan et al. studied echocardiographic measurements and functional status in stented Carpentier–Edwards (CE) and Toronto Stentless Porcine valve (SPV), (Duke Activity Status Index) assessed at 3 and 12 months. They found that perioperative morbidity and mortality was similar between groups at 12 months postoperatively. Cardiopulmonary bypass times were significantly prolonged in the SPV group. Maselli et al. studied the effect of four different types of prosthetic aortic valves on time course and extent of regression of left ventricular hypertrophy. They found that stentless or homograft aortic valve produces a faster regression of left ventricular hypertrophy. The same result was achieved by Walther et al. They found that regression of left ventricular hypertrophy occurs in all patients after aortic valve replacement but is enhanced after stentless valve implantation. Williams et al. studied left ventricular mass using magnetic resonance imaging (MRI) at 1 week, 6 months, and 32 months. At 32 months, measurement in diastole showed a reduction of 38% (P<0.01) in the stentless group compared with 20% (P=ns) in the stented group, and measurements in systole showed a 23% (P<0.01) and 13% (P=ns) reduction, respectively. A 30% decrease in left ventricular mass occurred in the early- and mid-term (12 months) periods after surgery with all types of bioprostheses [Tsialtas]. Advantages consisting of a progressive increase in transprosthetic effective orifice area (EOA), and physically active patients in particular may benefit from use of the stentless valve, because of its larger EOA [Tsialtas, Bleiziffer].

Clinical Bottom Line

Stentless valves allow a larger effective orifice area valve to be implanted with a lower mean and peak aortic gradient postoperatively. At six months several studies and a meta-analysis have shown superior left ventricular mass regression in the stentless valve groups. However, by 12 months the stented valve groups catch up in terms of mass regression and this significance disappears. There have been no definitively proven benefits for stentless valves.

References

1. Kunadian B, Thornley AR, de Belder MA et al. A Meta-analysis of valve haemodynamics and left ventricular mass regression for stentless vs. stented aortic valves. (Ann Thorac Surg; accepted for publication March 2007).
2. Ali A, Halstead JC, Cafferty F et al. Are stentless valves superior to modern stented valves? A prospective randomised trial. Circulation 2006; 114:I535–540.
3. Perez de Arenaza D, Lees B, Flather M et al. Randomised comparison of stentless vs. stented valves for aortic stenosis: effects on left ventricular mass. Circulation 2005; 112:2696–2702.
4. Perez de Arenaza D, Lees B, Flather M et al. Randomised comparison of stentless vs. stented valves for aortic stenosis: effects on left ventricular mass. Circulation 2005; 112:2696–2702.
5. Bakhtiary F, Schiemann M, Dzemali O et al. Stentless bioprosthesis improve postoperative coronary flow more than stented prostheses after valve replacement for aortic stenosis. J Thorac Cardiovasc Surg 2006; 131:883–888.
6. Totaro P, Degno N, Zaidi A et al. Carpentier-Edwards Perimount magna bioprosthesis: a stented valve with stentless performance. J Thorac Cardiovasc Surg 2005; 130:1668–1674.
7. Doss M, Martens S, Wood JP et al. Performance of stentless vs. stented aortic valve bioprosthesis in the elderly patient: a prospective randomised trial. Eur J Cardiothorac Surg 2003; 23:299–304.
8. Cohen G, Christakis GT, Joyner CD et al. Are stentless valves haemodynamically superior to stented valves? A prospective randomised trial. Ann Thorac Surg 2002; 73:767–775.
9. Maselli D, Pizio R, Bruno LP et al. Left ventricular mass reduction after aortic valve replacement: homografts, stentless and stented valves. Ann Thorac Surg 1999; 67:966–971.
10. Bleiziffer S, Eichinger WB, Wagner I et al. The Toronto root stentless valve in the subcoronary position is hemodynamically superior to the Mosaic stented completely supra-annular bioprosthesis. J Heart Valve Dis Nov 2005; 14:814–821.
11. Borger MA, Carson SM, Ivanov J et al. Stentless aortic valves are hemodynamically superior to stented valves during mid-term follow-up: a large retrospective study. Ann Thorac Surg Dec 2005; 80:2180–2185.
12. Chambers JB, Rimington HM, Hodson F et al. The subcoronary Toronto stentless vs. supra-annular Perimount stented replacement aortic valve: early clinical and hemodynamic results of a randomised comparison in 160 patients. J Thorac Cardiovasc Surg Apr 2006; 131:878–882.
13. Walther T, Falk V, Langebartels G, Kruger M et al. Prospectively randomised evaluation of stentless versus conventional biological aortic valves: impact on early regression of left ventricular hypertrophy. Circulation 1999;100(19 suppl): II6 –10.
14. Williams RJ, Muir DF, Pathi V et al. Randomised controlled trial of stented and stentless aorticbioprotheses: hemodynamic performance at 3 years. Semin Thorac Cardiovasc Surg 1999;11:93–7.
15. Santini F, Bertolini P, Montalbano G et al. Hancock versus stentless bioprosthesis for aortic valve replacement in patients older than 75 years. Ann Thorac Surg 1998;66:S99 –103.
16. Bove T, Van Belleghem Y, Francois K et al. Stentless and stented aortic valve replacement in elderly patients: Factors affecting midterm clinical and hemodynamical outcome Eur J Cardiothorac Surg. 2006 Nov;30(5):706-13.
17. Tsialtas D, Bolognesi R, Beghi C et al. Stented versus stentless bioprostheses in aortic valve stenosis: effect on left ventricular remodelling. Heart Surg Forum. 2007;10(3):E205-10.