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University of Alberta Hospital, 2D4.37 Walter MacKenzie Health Sciences Centre, 8440 112th St, Edmonton, AB, Canada T6G 2B7
(Email: dbross{at}cha.ab.ca).
de Vincentiis and colleagues [1] present a report on a retrospective series of 345 patients greater than 80 years of age who underwent aortic valve replacement. The operative mortality is low (7.5%) considering that more than half of these patients underwent concomitant other cardiac procedures and the postoperative quality of life was excellent for the survivors; perhaps a bit too good, because it is difficult to believe that 96% were in New York Heart Association functional class I or II for patients in this age range. Nevertheless, the authors do provide Short Form-36 data.
A strength of this article is that it is a large series with 100% follow-up.
The controversial aspect of this article is that the authors found that 42% of patients received a mechanical valve with statistically superior survival in comparison with those who received a tissue valve, despite the fact that these groups were preoperatively similar. This is a very controversial and surprising finding, given that a number of series show no survival benefit to one type of valve in comparison with another, even in very young patients who would be expected to have a survival benefit of a mechanical valve [2]. There are really only two explanations for the findings of this article: (1) either those that received a mechanical valve were healthier patients or (2) the addition of warfarin was beneficial to these patients by some other mechanism than preventing mechanical valve-related thromboembolism (ie, preventing nonvalve related thromboembolism from atrial fibrillation, pulmonary embolism, or another factor). Clearly, it is not due to structural deterioration of the bioprosthesis, as the survival advantage is present within the first 4 years after surgery. Other possibilities (such as the mechanical valve patients having better hemodynamic results) are theoretically possible, although unlikely, given that on average the mechanical valves were implanted into patients with calcified annuli, which were an average 2 to 3 mm smaller than the tissue valves. Nevertheless, postoperative aortic valve gradients and the prevalence of patient prosthesis mismatch data would have been useful additions to the article. Interestingly, patients with preoperative atrial fibrillation were slightly less likely to receive a mechanical valve than a bioprosthetic valve.
The most likely explanation remains that the surgeons operating on these patients were able to select healthier, more high-functioning patients to receive mechanical valves; thus, they lived longer. There is no data presented to support this thesis as the groups had equal representation for most known risk factors, except that more patients receiving mechanical valves underwent concomitant coronary revascularization. Nevertheless, there is good data in the literature to support subtle measures of patients well being, having important implications for surgical risk. The preoperative Short Form-36 Physical Component Summary has been shown by others to be a powerful statistically significant predictor of 6-month mortality for coronary bypass patients, even after adjustment for other known risk factors [3]. A 10-point lower score in Rumsfeld and colleagues’ [3] article corresponded with a 39% risk for increased mortality at 6 months, greater than the risk associated with an elevated serum creatinine or smoking.
The alternative explanation is that there is really some advantage to elderly patients receiving a mechanical valve, whether from the valve itself or from its associated anticoagulation. A randomized prospective trial of mechanical versus biological valves would answer the question, but it would be highly unlikely to receive support from most centers. At our institution, of the 108 patients greater than 80 years of age who received an aortic valve prosthesis between 2002 and 2006, only one had a mechanical valve implanted. A more realistic trial might compare warfarin with acetylsalicylic acid for the elderly receiving biological valves in the aortic position, but the significantly elevated rate of cerebrovascular events, particularly hemorrhaging, as documented in the mechanical valve group in the present study should raise concerns.
Finally, the overall excellent results of this large surgical cohort provide a good group for comparison with series of elderly undergoing percutaneous aortic valve replacement. In their enthusiasm to adopt newer and less invasive approaches to aortic valve replacement in patients deemed to be high risk, surgeons and cardiologists need to be aware of the low risk associated with conventional surgery.
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