Ann Thorac Surg 2009;87:350-351. doi:10.1016/j.athoracsur.2008.05.026
© 2009 The Society of Thoracic Surgeons
Correspondence
Design Flaws Make Conclusions Difficult
Nishith Patel, MB(BCh), MRCS
Department of Cardiac Surgery, Bristol Royal Infirmary, Marlborough St, Bristol, BS2 8HW United Kingdom
(Email: patel_nishith{at}hotmail.com).
To the Editor:
I read with interest the article by De Vincentiis and collegues [1] on aortic valve replacement (AVR) in octogenarians and a comparison of prostheses in this population. This is a topic of immense interest because of the expanding elderly population in affluent nations, and this article contributes to the expanding literature [2, 3] in this area.
However, I believe this retrospective cohort study has design flaws that make it difficult to draw any conclusions. These are detailed below:
- (1) Primary Outcome Variable—Authors do not mention their primary outcome measure. This obviously makes it difficult to perform power and sample size calculations.
- (2) Power of Study—There is no mention of sample size and power calculations. Therefore, the study may be underpowered to detect any difference, and it makes the study open to type II errors.
- (3) Aim of Study—The exact aim of the study is difficult to delineate. Does it aim to determine the outcomes in all octogenarians undergoing AVR or is its main focus the comparison of outcomes between mechanical and biological prostheses in octogenarians undergoing AVR?
- (4) Comparability of Groups—Many patients (43.5%) in the cohort had other associated procedures. The impact of additional procedures (such as coronary artery and mitral valve surgeries) on mortality is not yet clear [4, 5]. A greater proportion of group 2 had additional procedures. Therefore, these groups are not comparable. The authors could have matched the patients by age and additional procedures or excluded patients with additional procedures.
- (5) Inadequate Follow-up—It is difficult to determine whether all the patients were followed-up for the same duration. There is no note of when the last patient was recruited. In survival analyses it is important to consider patient years rather than calendar years.
The design flaws of this cohort study just mentioned make it difficult to draw conclusions on this interesting and relevant topic.
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References
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- De Vincentiis C, Kunkl AB, Trimarchi S, et al. Aortic valve replacement in octogenarians: is biologic valve the unique solution? Ann Thorac Surg 2008;85:1296-1301.[Abstract/Free Full Text]
- Vicchio M, Della Corte A, De Santo LS, et al. Tissue versus mechanical prostheses: quality of life in octogenarians Ann Thorac Surg 2008;85:1290-1295.[Abstract/Free Full Text]
- Kolh P, Lahaye L, Gerard P, Limet R. Aortic valve replacement in the octogenarians: perioperative outcome and clinical follow-up Eur J Cardiothorac Surg 1999;16:68-73.[Abstract/Free Full Text]
- Langanay T, De Latour B, Ligier K, et al. Surgery for aortic stenosis in octogenarians: influence of coronary disease and other comorbidities on hospital mortality J Heart Valve Dis 2004;13:545-552.[Medline]
- Kobayashi KJ, Williams JA, Nwakanma L, Gott VL, Baumgartner WA, Conte JV. Aortic valve replacement and concomitant coronary artery bypass: assessing the impact of multiple grafts Ann Thorac Surg 2007;83:969-978.[Abstract/Free Full Text]
Related Article
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Reply
- Marisa Di Donato and Carlo De Vincentiis
Ann. Thorac. Surg. 2009 87: 351.
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M. Di Donato and C. De Vincentiis
Reply
Ann. Thorac. Surg.,
January 1, 2009;
87(1):
351 - 351.
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