Cognitive Decline After Coronary Artery Surgery

We read with interest the recent article by Selnes et al¹ that significant cognitive decline occurs 5 years after individuals have undergone coronary artery bypass grafting (CABG). Whereas this and related findings have important ramifications for the treatment of these individuals, several statistical and methodological issues cast doubt on the reliability of the results.

The difficulties in analyzing the neuropsychological results are well recognized.² In particular, the use of group mean change instead of individual scores may obscure individual patient changes. The same authors, in an earlier description of neuropsychological changes at 1 year in the same patient group, stated the following: "[A]s group measures of central tendency may obscure important changes in performance in individuals . . . we examined patterns of cognitive change in all patients individually, using the change in each patient's performance from preoperative testing as the outcome."³(p512) We are intrigued as to why change in cognitive performance was not analyzed at the level of individual patients, particularly because this method was used by the same authors in the previous article and with the same patient sample. Their use of group change as an alternative outcome measure masks the decline they previously observed at 1 year³ using individual changes, and instead suggests an improvement.