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Interact CardioVasc Thorac Surg 2007;6:665-672. doi:10.1510/icvts.2007.160051 © 2007 European Association of Cardio-Thoracic Surgery
Is a stentless aortic valve superior to conventional bioprosthetic valves for aortic valve replacement?Department of Cardio-thoracic Surgery, Aberdeen Royal Infirmary, Aberdeen, AB25 2ZN, UK Received 22 May 2007; received in revised form 15 June 2007; accepted 18 June 2007
*Corresponding author. Tel.: +44-7849729149; fax: +44-1224553506.
A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether a stentless valve is superior to conventional stented valves when tissue aortic valve replacement is performed. Altogether more than 515 papers were found using the reported search, of which 16 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. We conclude that 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. So the ‘eminent speaker from the floor’, was right with his statement, that there have been no definitively proven benefits for stentless valves.
Key Words: Stentless valve; Stented valve; Thoracic surgery; Aortic valve replacement
A best evidence topic was constructed according to a structured protocol. This is fully described in the ICVTS [1].
In [patients undergoing a bioprosthetic aortic valve replacement] is [a stented or a stentless valve] superior [for achieving left ventricular recovery].
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.
Medline 1950 to May 2007 using OVID interface [aortic valve replacement.mp OR exp aortic valve/] AND [Stentless.mp OR Stented.mp].
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. These are presented in Table 1.
Kunadian et al. [2] 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. [13] 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. [14] in there follow-up for eight years. On the other hand, Borger et al. [17] 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. [3] 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. [4] 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. [5] 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. [6, 12] 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. [7] 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. [8] 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. [9] 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. [10]. 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. [11] 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 [15]. 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 [15, 16].
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.
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Abstract
1. Introduction