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Eur J Cardiothorac Surg 2006;30:713-715
© 2006 Elsevier Science NL
Department of Cardiothoracic Surgery, University Hospital, Coimbra, Portugal
* Tel.: +351 239 400418; fax: +351 239 829674. (Email: antunes.cct.huc{at}sapo.pt).
In this issue of the Journal, Bové et al. [1] report a retrospective study of 145 elderly patients (mean age 75 years) with aortic stenosis who received a Toronto stentless prosthesis and compare them with 110 similar patients (mean age 76 years) who received a stented Carpentier-Edwards valve. Although the definition of elderly is not disclosed, it can be presumed that the classical cut-off age of 65 years was used. However, the series is obviously composed of a majority of patients in their late 70s and in their 80s. They were followed clinically and by Doppler-echocardiography for a mean of 47–56 months to assess transprosthetic gradients and to accompany the evolution of LV wall-mass (LVM) and the respective index (LVMI), which was analysed and correlated to ‘specific prosthesis and patient-related factors’, especially patient-prosthesis mismatch (PPM). Effective orifice areas (EOA) and indexed EOA were estimated from available in vitro tables rather than in vivo (echocardiographic), which could have been more representative.
The authors found that clinical improvement occurred in most patients and was independent of PPM. Although there was a significant difference of survival at the 5-year period in favour of the stentless valve group, this difference had disappeared after 8 years. Only advanced age, NYHA class IV and excessive pre-operative LV hypertrophy were identified as independent predictors of late mortality. The type of prosthesis did not come up as a factor of late survival. Furthermore, they found that both types of prostheses were equally effective in terms of decreasing transprosthetic gradients and LVMI regression. Only excessive pre-operative LV hypertrophy compromised ventricular remodelling and early LVMI regression at 1 year was optimized by avoidance of PPM. Interestingly, after the initial regression, LVM started to increase again after 3 years, independent of the transvalvular gradients. Only systemic hypertension was found to significantly influence late LV remodelling.
However interesting the comparison between these two types of prostheses may be, this article cannot contribute to solve the problem of patient-prosthesis mismatch. Evidently, and despite the authors’ statements to the contrary, their two population groups are not identical. There must have been some bias in the selection of the patients for each of the two prostheses, judging from the significant differences in gender, height, incidence of diabetes, atrial fibrillation and previous cardiac surgery, which obviously influenced the long-term results. In the medium to long-term survival, there is a diversion of the curves of the two types of valves at the mid-term follow-up, but then there is a strange re-approximation at the later period. Although the number of patients at risk at this late time interval was relatively small and may have influenced the statistics, the effect of old age is difficult to ascertain.
From this point of view also, the article is rather inconclusive, but the findings of an early influence of pre-operative LV hypertrophy and of systemic arterial hypertension in late remodelling of the LV are rather interesting and may constitute its most important message. In two recent studies published in our Journal, Fuster et al. [2] had also identified very high LVMI as a determinant factor of mortality, and Imanaka et al. [3] had found continued systemic hypertension to be a significant factor for increased long-term mortality.
The clinical outcome after AVR for aortic stenosis has been the matter of intense debate. It has been demonstrated that long-term survival is associated with adequate LVM regression, but the influence of the type of prosthesis and of PPM remains controversial. There are as many reports in recent literature confirming a detrimental effect of PPM as there are studies which deny such influence, at least for moderate degrees of PPM, and they are adequately cited in the article under discussion. In two of the largest series published, Borger et al. [4], from Toronto, and Ennker et al. [5], from Germany, the latter involving exclusively elderly patients, report contrasting results which may be related to the different prostheses used in each study.
Everybody agrees that the use of extremely small prostheses should be avoided, especially in big and active patients, and several methods to insert prostheses larger than the diameter of the natural annulus have been described and applied successfully in countless patients. On the other hand, newer prostheses have larger effective orifice areas and are, therefore, more efficient. Among other potential advantages, stentless bioprostheses are said to have superior haemodynamic characteristics, including lower gradients for matching annular implantation sizes, therefore favouring LVM regression. Nevertheless, this has not been conclusively proven, and most recent prospective randomized trials have failed to confirm the haemodynamic superiority of stentless valves that appeared to have been shown in earlier studies [6]. Furthermore, the proclaimed haemodynamic superiority of stentless bioprostheses does not necessarily translate into improved clinical outcome, as has been demonstrated by some randomized studies.
The current study by Bové et al. appears to indicate that factors other than prosthesis type and size, but which might influence the respective choice, may play an important role. Identifying these factors would have obvious clinical implications, as it would help to decide, for example, whether to offer surgery to asymptomatic patients with significant AS and severe LV hypertrophy and to recommend more aggressive post-operative treatment of hypertension.
On the other hand, the impact of these factors and also the use of stentless versus stented prostheses in elderly patients remain questionable. Although this was not a factor in the authors’ experience as well as in the experience of others’, operative mortality may be higher than that observed with easier-to-implant stented prostheses, especially in the hands of non-experienced surgeons, an important factor to have in mind when making generally applicable recommendations.
It is obvious that strict guidelines are impossible to formulate, but the choice of the prosthesis – and its size – must consider not only patient-specific variables, but also the experience of the surgical team. It appears, however, that only extremes of PPM may have a significant deleterious effect on the clinical outcome and long-term survival. Although radical options, including the generalized use of annular enlargement procedures, appear not to be warranted, especially in the elderly and relatively less-active population, the same holds true for widespread indication for use of stentless bioprostheses. All modern prostheses, both mechanical and biological, of appropriate size (equal to or above 21) are adequate in these circumstances, perhaps with the exception of very large individuals.
Anything else remains speculative.
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