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Ann Thorac Surg 2004;77:1635
© 2004 The Society of Thoracic Surgeons

Invited commentary

Department of Anesthesiology Mount Sinai School of Medicine, One Gustave L. Levy Place Box 1010 New York, NY 10029, USA

Suzan Uysal, PhD

Department of Anesthesiology Mount Sinai School of Medicine, One Gustave L. Levy Place Box 1010 New York, NY, 10029, USA

e-mail: david.reich{at}mssm.edu
e-mail: suzan.uysal{at}mssm.edu

We are very pleased that Miyairi and colleagues have performed this prospective study of a large clinical cohort using psychometric testing. The conclusion that long periods of retrograde cerebral perfusion (RCP) were associated with negative outcomes is an important clinical finding that has implications for future approaches to cerebral protection in complex thoracic aortic repairs. Our comments are intended to place this study in context.

A limitation of the study is the authors' choice of the WAIS-R as a neurocognitive outcome measure. The WAIS-R is a psychometric "intelligence" test that was originally developed as the Wechsler-Bellevue scale in 1939, prior to current conceptualizations of the neural basis of cognition. It has remained substantially the same since that time, as most revisions have been aimed at improving the test's psychometric properties. It is not, however, a battery of neuropsychological tests that specifically assesses the major domains of cognitive function (attention, memory, visuospatial functions, language, construction, and executive functions). The WAIS-R is not effective at identifying two of the most prevalent forms of neuropsychological dysfunction—dysexecutive syndrome and anterograde amnesia. Other problems include improving performance with repeated administration over time (practice effects) and lack of normative data for patients over 74 years of age.

The statistical treatment of the data requires comment. One of the advantages of the WAIS-R is that the raw subtest scores are easily converted to normalized age-scaled scores, allowing easy comparisons among the results of the different subtests. If we consider the continuous data score of each subtest an independent observation, the statistical analysis must consider two factors: (1) type of procedure (CABG versus different periods of RCP); and (2) the two measurements of postoperative WAIS-R results compared with baseline. We would have preferred to see Bonferroni or other multiple comparison corrections used for interpreting differences among the groups.

Another problem with analyses of this clinical type is that mean scores across the entire cohort can obscure important changes that occur in a small proportion of the patients. In the neuropsychological analyses of CABG outcome, the incidence of cognitive decline at 4–6 months is quite low. Therefore, an alternative approach that is also probably more appropriate given the overlap of the subtests is the classification of patients into normal and dysfunctional groups based upon factor scores that are combinations of the subtests into the verbal ability, perceptual organization, and attention domains. Categorical analyses can then be performed based on the incidence of dysfunction.

In this study, three WAIS-R subtests showed postoperative decline following long periods of RCP: Digit Span, Picture Completion, and Picture Arrangement. The authors described these subtests as measures of attention, leading them to conclude that prolonged RCP puts patients at risk for a selective impairment in attention. We question this conclusion, because factor analytic studies of the WAIS-R subtests do not support two of these subtests—Picture Completion and Picture Arrangement—as sensitive measures of dysfunction in the attention domain. Furthermore, two of the three WAIS-R subtests that are sensitive measures of attention did not decline—Digit Symbol and Arithmetic.

Despite these criticisms, the work of Miyairi and colleagues is an important step forward in the analysis of thoracic aortic surgical outcomes. Neuropsychological testing is essential when evaluating the efficacy of any neuroprotective strategy. Accordingly, we expect that more thoracic aortic surgical programs will emulate the efforts of these investigators.

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