CORRESPONDENCE: LETTER TO THE EDITOR
Body Size and the Early Mortality Gender Gap in Coronary Artery Bypass Grafting Surgery
Robert H. Habib, PhD* and
Anoar Zacharias, MD
* Cardiopulmonary Research, St. Vincent Mercy Medical Center, 2213 Cherry Street, ACC Bldg, Suite 309, Toledo, Ohio 43608 (Email: robert_habib{at}mhsnr.org).
Humphries et al. (1) investigated gender differences in 30-day mortality after isolated coronary artery bypass grafting (CABG) for the entire province of British Columbia from 1991 to 2004. The authors report a substantial trend for improved early CABG mortality in women over this 14-year period. Yet there remains a significant 42% worse 30-day mortality in women even after adjustment for differences in age, comorbid conditions, and surgical factors. Lastly, they report that this gender gap in early CABG outcomes is decreased and is no longer statistically significant (odds ratio 1.26, 95% confidence interval 0.96 to 1.64) when their data is adjusted to body surface area (BSA). The authors explained the latter by a presumed association between lower BSA and smaller coronary vessel size.
We concur with the authors that patients with lower BSA are more likely to have smaller coronary targets that are more difficult to revascularize with potential adverse implications on outcomes. This, however, ignores other important factors that are associated with body size and are especially true in case of CABG with cardiopulmonary bypass such as in their series (97% on-pump). A strong association between small body size—disproportionately represented by women—and greater on-pump hemodilution and more frequent administration of packed red blood cell (RBC) units is well established (2,3). Worse early CABG outcomes have been associated with both lower on-pump hematocrits (2–4) and RBC transfusions (5,6). We contend that the authors’ reported 30-day mortality odds ratio of 1.26 in women compared with men would be further reduced if their multivariate adjustment included hemodilutional anemia and transfusion data. This perspective is important, because in contrast to coronary vessel size, which is a fixed patient characteristic, both of these size-related risk factors are potentially modifiable. Specifically, hemodilutional anemia and related use of blood products may be mitigated through specific practices such as: 1) avoidance of cardiopulmonary bypass (off-pump surgery); 2) use of miniaturized bypass circuits combined with retrograde autologous priming; and/or 3) implementation of conservative transfusion policies.
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References
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- Humphries KH, Gao M, Pu A, Lichtenstein S, Thompson CR. Significant improvement in short-term mortality in women undergoing coronary artery bypass surgery (1991 to 2004) J Am Coll Cardiol 2007;49:1552-1558.[Abstract/Free Full Text]
- DeFoe GR, Ross CS, Olmstead EM, et al. Northern New England Cardiovascular Disease Study Group Lowest hematocrit on bypass and adverse outcomes associated with coronary artery bypass grafting Ann Thorac Surg 2001;71:769-776.[Abstract/Free Full Text]
- Habib RH, Zacharias A, Schwann TA, Riordan CJ, Durham SJ, Shah A. Adverse effects of low hematocrit during cardiopulmonary bypass in the adult: should current practice be changed? J Thorac Cardiovasc Surg 2003;125:1438-1450.[Abstract/Free Full Text]
- Koch CG, Li L, Duncan AI, et al. Morbidity and mortality risk associated with red blood cell and blood-component transfusion in isolated coronary artery bypass grafting Crit Care Med 2006;34:1608-1616.[CrossRef][ISI][Medline]
- Engoren M, Habib RH, Zacharias A, et al. Effect of blood transfusion on long-term survival after cardiac surgery Ann Thorac Surg 2002;74:1180-1186.[Abstract/Free Full Text]
- Habib RH, Zacharias A, Schwann TA, Riordan CJ, Durham SJ, Shah A. Effects of obesity and small body size on operative and long term outcomes of coronary artery bypass surgery: a propensity matched analysis Ann Thorac Surg 2005;79:1976-1986.[Abstract/Free Full Text]
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