Ann Thorac Surg 2008;85:64. doi:10.1016/j.athoracsur.2007.09.023
© 2008 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Invited commentary
Todd K. Rosengart, MD
Department of Surgery, Stony Brook University, Health Sciences Center, 19th Floor, Room 080, Stony Brook, NY 11794-8191
(Email: todd.rosengart{at}stonybrook.edu).
The preceding study by Van Dijk and colleagues [1] is an important contribution to a growing recent literature that serves as a counterpoint to earlier articles reporting significant cognitive decline in patients undergoing coronary bypass surgery (ie, open heart surgery). Having previously demonstrated a lack of difference in cognitive decline between off-pump and on-pump coronary artery bypass grafting (CABG), the authors have now grouped these cohorts together and compared them with an age-matched control group without evidence of coronary disease. They report a nonsignificant odds ratio of 1.37 of cognitive decline for 5 years in CABG patients.
Putting Type II sample size statistical concerns aside, a number of issues are raised by this study. First, the present and other recent CABG and cognitive studies highlight the absolute importance of research controls. As compared with earlier uncontrolled studies, the present study suggests that at least half of the decline reported after CABG may be attributable to the "natural history" of cognitive function in this relatively aged population (ie, 16% vs 34% decline in control vs CABG groups). Several prior studies have similarly suggested that (cerebrovascular) atherosclerosis in the CABG population (not controlled for in this or most previous studies) can also lead to cognitive decline absent CABG surgery. Similar outcomes have been demonstrated after other major surgical procedures and were also related to educational differences. Such caveats significantly undermine claims of cognitive decline caused specifically by CABG.
The present study also raises the possibility of false positive results. This and most previous studies provide only limited descriptions of the conduct of cardiopulmonary bypass. Failure to use potential neuroprotective measures, such as echocardiographic assessment of the aorta and maintenance of adequate cerebral perfusion pressures, could lead to potentially avoidable cerebral injury and cognitive decline. Failure to report the use of such neurocognitive best practices could lead to "apples to oranges" comparisons in researchers’ analyses of the literature. Whereas myocardial protection techniques were innovated after the reporting of myocardial injury a generation ago, such deficiencies could slow efforts to develop analogous cerebral protection techniques.
Finally, the current report reflects inherent challenges in the "black art" of neurocognitive analysis, complex studies subject to wide discrepancies in execution and interpretation. These complexities (eg, selecting appropriate definitions for "dysfunction") can easily lead to inadvertent misinterpretation of cognitive data. A meticulously adhered to consensus in performing and interpreting cognitive analyses will therefore also be critical to innovation in this area of needed improvement in cardiac surgery.
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References
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- Van Dijk D, Moons KGM, Nathoe HM, et al. Cognitive outcomes five years after not undergoing coronary artery bypass graft surgery Ann Thorac Surg 2008;85:60-64.[Abstract/Free Full Text]
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