Wolozin, at Boston University, together with colleagues at Pfizer in Groton, Connecticut, and Northwestern University, the University of Chicago, and that VA Hospital in Hines, all in Illinois, followed over 5,000 patients who had undergone the CABG procedure between October 1996 and September 1997. First author Todd Lee and colleagues found that 119 of the patients developed AD during the five years following their operation. As a control, they also followed patients (just over 3,900 individuals) who had undergone angioplasty (percutaneous transluminal coronary angioplasty or PTCA). The relative risk for AD in the CABG group was almost twice that in the PTCA group—1.7-fold. The findings confirm previously documented postoperative cognitive decline in much smaller groups of patients following CABG surgery (see Selnes et al., 2001 and Newman et al., 2001). The analysis “demonstrates that there is a significant association between CABG surgery and subsequent cognitive decline, as demonstrated by the incidence of AD, when compared to a cohort undergoing PTCA,” write the authors.

Why the CABG procedure should increase the risk for AD is not entirely clear, but Lee and colleagues suggest that it could be due to an exacerbated decrease in cognitive, or neuronal, reserve. Neuronal reserve has been used to explain why a loss of brain matter can be more devastating to some than to others (see Buckner, 2004), and could be compromised by hypoperfusion during surgery (see ARF Live Discussion on the vascular hypothesis of AD).

The role of hypoperfusion in late-onset dementia is supported by the second paper. Using magnetic resonance imaging, Westendorp and colleagues at Leiden University, The Netherlands, measured total cerebral blood flow in a group of 48 volunteers, made up of 15 young, 16 elderly with optimal cognition, and 17 elderly patients with dementia (the study was first published online July 12). First author Aart Spilt and colleagues found that although those elderly volunteers who still retained optimal cognition had reduced blood flow compared to the younger group (551 mL/min versus 742 mL/min), those elderly with dementia fared even worse, having an average total cerebral blood flow of only 443 mL/min. The data are even more dramatic given that subjects with any vascular dementia, which would presumably skew the data toward even lower blood flow measurements in the dementia group, were excluded from the study.—Tom Fagan.

Reference:
Lee TA, Wolozin B, Weiss KB, Bednar MM. Assessment of the emergence of Alzheimer’s disease following coronary artery bypass graft surgery or percutaneous transluminal coronary angioplasty. J. Alzheimer’s Disease. August 2005;7:319-324. Abstract

Spilt A, Weverling-Rijnsburger AWE, Middelkoop HAM, van Der Flier WM, Gussekloo J, de Craen AJM, Bollen ELEM, Blauw GJ, van Buchem MA, Westendorp RGJ. Late-onset dementia: structural brain damage and total cerebral blood flow. Radiology. 2005;236:990-995. Abstract