Prevalence and patterns of cognitive impairment in acute coronary syndrome patients: A systematic review

Acute coronary syndrome (ACS) continues to cause significant impact personally, socially and economically across the world. Important improvements in the immediate management of ACS have resulted in increases in survival from the initial event1,2 but benefit in long term survival is dependent on appropriate lifestyle changes and adherence to secondary prevention medication.3 Patients with high adherence to secondary prevention medication have a significantly reduced risk for all-cause mortality and major adverse cardiovascular events.3 There are a variety of influences which may affect a patient’s ability to make these modifications, including social, financial, educational and cognitive factors. Cognitive impairment is a potential obstacle for secondary prevention and self-management; however, its prevalence in the ACS population and its relationship to outcomes is poorly understood. Cognitive impairment can cause widespread difficulties with memory, language, attention, concentration, task completion and decision making, which may significantly affect a patient’s ability to initiate lifestyle changes.4 Patients with ACS have been identified as having an increased risk of developing cognitive impairment and dementia.5 In this issue of the journal, Zhao and colleagues6 explore this issue in a systematic review to investigate the prevalence and patterns of cognitive impairment in ACS patients. The authors have carried out a literature review up until March 2019, concentrating on original, peer reviewed studies in English. The nine studies selected for the review ranged widely in the number of study participants and age of the patients. There was also a significant variation in the screening tools used in the various studies to measure cognitive impairment, with eight different tools being used in the nine studies. In addition, the severity of the cognitive impairment measured in each study also ranged from mild to severe. The timing of the assessment of cognitive impairment varied considerably between during the hospitalisation for ACS to five years post event. The study found a prevalence of cognitive impairment of between 9% and 85%, dependent on the severity of cognitive impairment assessed and the time when the assessment took place. There did not appear to be a significant difference between the prevalence of cognitive impairment in the early recovery period and the longer term although there was large variability in the percentages reported from the individual studies. There was no stratification of cognitive impairment prevalence in age groups and it is therefore not possible to determine whether there is any association between age and cognitive impairment. The authors note that the different screening tools appeared to have different sensitivity in identifying cognitive impairment in the early post ACS period. This makes generalisation of the results difficult as several of the screening tools were used in only one study. Only two of the studies reviewed reported domains for cognitive impairment. These suggested that the verbal fluency and memory domains were most affected in moderate to severe cognitive impairment and the attention domain in mild cognitive impairment. The authors conclude that cognitive impairment is a common finding in post ACS patients and probably persists over time. The actual prevalence rate could not be determined from this study due to the heterogeneity of the studies involved in the review. The authors set out to establish the prevalence and patterns of cognitive impairment in the ACS population and although they have provided some very useful information on this topic, they have not really been able to achieve their aim. The studies they reviewed included a large number of patients, which should have helped the authors draw some conclusions; however, the large variations between the studies has made this difficult to achieve. Cognitive impairment is an important issue in the management of patients post ACS; however, the reader is left with many unanswered questions. Which is the most appropriate screening tool to use in the assessment of cognitive impairment? When should the tool be used? Which domains of cognitive impairment are particularly affected and is this variable at different time periods? If we are to measure cognitive impairment in ACS patients we need to be sure that it is done correctly before conclusions can be drawn. Cognitive impairment does appear to be a significant problem. In one study of older patients undergoing invasive management of non-ST segment ACS (mean age 80.5 ± 4.8 years), undiagnosed cognitive impairment was identified as being highly prevalent.7 The authors of this study also found that recurrent myocardial infarction was independently associated with cognitive decline at one year. In another study, frailty was found to be associated with an increased risk of major events and hospital readmissions in elderly ACS patients.8 Silva and colleagues9 found a degree of cognitive impairment in 85% of their sample of 53 patients undergoing cardiac rehabilitation three months after an ACS, with the majority showing impairment in verbal fluency. Verbal fluency was related to schooling, which may affect an individual’s ability to express themself and to understand the need for lifestyle changes. They concluded that the prevalence of neurocognitive dysfunction was high in this patient group, although their sample size was small.9 Bedside measurement of mental status in elderly patients post ACS within 48 h of admission demonstrated cognitive impairment in approximately one-third of patients. This was then found to be associated with an increased risk of mortality at one year and an increase in rehospitalisation at three months.10 Cognitive impairment has also been identified in patients following coronary artery bypass surgery (CABG).11 From their large sample, the authors of this study discovered that cognitive impairment occurred in approximately 43% of patients acutely, which then reduced to 19% at 4–6 months post operatively but subsequently increased to 25% of patients between six months and one year. In the long-term between one and five years post operatively, cognitive impairment increased and was seen in approximately 40% of patients. Whilst the high prevalence rate immediately post operatively may be at least partially explained by the anaesthetic and the use of analgesia, the increase in the long term is unexplained and has implications for caring for this patient group. Cognitive performance has been shown to affect patients’ ability to maintain disease-related knowledge following cardiac rehabilitation, especially in patients following CABG, suggesting that patients in this group need to have education tailored to them.12 Cognitive impairment has also been identified in other patients with chronic diseases, such as those undergoing peritoneal dialysis,13 and following transient ischaemic attack (TIA), although cognitive impairment was seen to be worse in ACS patients at one year when compared with patients following a TIA.14 Non-adherence to medication following ACS is associated with an increased risk of recurrent events. The association of cognitive impairment with medication non-adherence was investigated by Marzec and colleagues. They discovered an association between mild neurocognitive disorder (MNCD) and medicine adherence and concluded that patients should be screened for MNCD during hospital admission for ACS to identify patients at high risk of non-adherence, so that an adherence intervention could be targeted at this at-risk group.15 There does appear to be sufficient evidence to suggest that cognitive impairment is likely to adversely affect mortality and morbidity following an ACS; however, the exact mechanism remains unknown. In their discussion, the authors of this review highlight the potential adverse effect of some secondary prevention medication in patients with cognitive impairment. The inflammatory state post ACS may also be a contributory factor to cognitive impairment. Persistently high levels of C-reactive protein post ACS have been reported as being predictive of the development of post-traumatic stress disorder. Interventions to lower inflammation might therefore be warranted to reduce this.16 There is considerable evidence that depression and anxiety following an ACS lead to an increased risk of mortality.17,18 Anxiety and depression are more prevalent in women and there is evidence to suggest that these problems are undertreated.19 The link between anxiety and depression and cognitive impairment has not been explored but both problems can lead to reduced compliance with secondary prevention measures. This review certainly leaves the reader feeling that there is an important aspect of post ACS care that is being missed in most patients. However, before screening for cognitive impairment in all ACS patients can be implemented, there needs to be further research to establish factors such as the optimal time for the screening and which tool should be used. Also, should all patients be tested or just the older age group? Investigation into whether all types of ACS are similarly affected would also help clinicians to target the most at-risk groups. It does appear that those of us caring for ACS patients need to be aware of cognitive impairment and its potential impact on the recovery and survival of patients. Mild cognitive impairment is potentially treatable, and identifying and treating such patients may delay progression to dementia. Those with moderate to severe cognitive impairment may progress to dementia and may require additional support and input from the healthcare team. Strategies to help patients who are identified with cognitive impairment will therefore need to be implemented to reduce risk, improve outcomes and promote self-care. The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. The author(s) received no financial support for the research, authorship, and/or publication of this article.