Clinical PaperSurvivors of cardiac arrest with good neurological outcome show considerable impairments of memory functioning☆
Introduction
Global or regional cerebral hypoperfusion caused by stroke, traumatic brain injury and even coronary artery bypass (CABP) surgery, are well known as effectors for various types of dysfunction in cognitive performance including memory deficits.1, 2, 3 In regard to these findings, the potential effects of cardiac arrest on cognitive performance have been targeted. The cerebral performance category (CPC) scale is a well established tool for evaluation of neurological damage after cardiac arrest and describes patients mental ability from CPC 1 (=return to normal cerebral performance) to CPC 5 (=brain death).4 However, within animal-models both neuropathological and neuroimaging studies revealed specific vulnerability of hippocampal regions after global cerebral ischemia due to cardiac arrest.5, 6 Human data in this context remain scarce and not conclusive. In terms of neurobiological effects studies appear to converge in indicating that global cerebral hypoperfusion may lead to focal lesions especially in the hippocampal region.7, 8 The hippocampal region is essential for learning and the transfer of new information in the declarative memory. Site of long-term memory and short-term recall are the neo-cortex and numerous subcortical regions, with which the hippocampus has strong reciprocal connections (see Fig. 1).
In terms of psychological consequences, previous studies empirically testing the associated cognitive profile reported significant cognitive deficits in cardiac arrest survivors.9, 10, 11, 12, 13, 14 However, the exact pattern of impairment still appears to be underspecified.15, 16 While early reports have used rather crude methods of assessing cognitive functioning such as the Mini Mental State Examination,17 recently, first studies have investigated cognitive functioning using a variety of established cognitive tests.9, 18
Our study follows up on previous work exploring potential memory deficits in cardiac arrest survivors extending the existing literature in three aspects. First, we prospectively tested for potential memory deficits applying an age, sex and education matched control group. Second, we aimed at delineating potential memory deficits using a comprehensive battery of retrospective and prospective short and long-term memory measures. Third, we aimed at disentangling potentially different performance patterns in cardiac arrest patients according to their state of consciousness at time of admission to our department as well as according to their overall neurological status at time of testing.
Section snippets
Study population
We prospectively enrolled 33 patients (23 [70%] male, age 50 [±15] years) after cardiac arrest admitted to the Department of Emergency Medicine at Vienna General Hospital, a university affiliated tertiary care center. To be included in our study, patients had to be at least 18 years old and had to show CPC 1 or 2. Patients were excluded if they had insufficient knowledge of the German language, were unable to speak and if they had suffered any cerebrovascular incident or disease of the central
Results
Between May 1st, 2004 and April 30th, 2005 all patients admitted after cardiac arrest (n = 174) were screened and finally 33 patients were included in our study (Fig. 2). Bystander CPR was performed in 27.3% (n = 9) of those cases.
Discussion
Sudden cardiac arrest survivors, who were categorized as neurologically intact according to conventional CPC measures, were revealed to show reduced memory performance in several but not all examined memory dimensions. Especially, resource-demanding memory tests such as delayed free recall, learning, working memory, prospective memory and prose recall were affected. However, short-term memory processes, even though tested via free recall tests, as well as recognition memory were revealed to be
Limitations
As one potential limitation one might argue that it seems quite early to perform extensive cognitive testing 4 weeks after a cardiac arrest. However, previous studies have successfully tested patients a few weeks after cardiac arrest, stroke and traumatic brain injury. A potential lack in follow-up analysis, as well as a lack in the analysis of recovery or decline in the study population has to be mentioned as a limitation. Nevertheless, examining the research questions of the present study
Conclusion
Our findings have several conceptual, clinical and methodological implications. From a conceptual perspective, memory function after cardiac arrest was found to be particularly impaired in resource demanding memory qualities such as delayed recall or working and prospective memory. In contrast, basic short-term memory storage appeared to be spared. Future studies will have to delineate possible conceptual loci of this impairment.
Conflicts of interest statement
No conflicts of interest to declare.
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2014.11.009.