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European Journal of Heart Failure 2006 8(5):494-501; doi:10.1016/j.ejheart.2005.11.013
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© 2006 European Society of Cardiology

Prognostic importance of cognitive impairment in chronic heart failure patients: Does specialist management make a difference?

Skye N. McLennana, Sue A. Pearsona, Janette Cameronb and Simon Stewarta,c,*

a University of South Australia, Division of Health Science Australia
b Deakin University, School of Nursing Australia
c Division of Health Science, University of Queensland, School of Medicine Australia

* Corresponding author. School of Nursing and Midwifery, University Of South Australia, City East Campus, North Terrace, Adelaide, SA 5000, Australia. Tel.: +61 08 8302 1115, +61 04 3830 2111 (Mobile); fax: +61 08 8302 2337. E-mail address: simon.stewart{at}unisa.edu.au


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 
Background: Cognitive impairment is common among chronic heart failure (CHF) patients.

Aims: To determine the prognostic significance of cognitive impairment in patients participating in a randomized study of a CHF management program (CHF-MP).

Methods: CHF patients were randomized to a CHF-MP (n=100) or usual care (n=100). Baseline cognition was assessed using the Mini Mental Status Examination (MMSE). Five-year all-cause mortality, and combined death-or-readmission, were compared on the basis of the presence (MMSE 19–26) or absence (MMSE >26) of cognitive impairment.

Results: 27 patients (13.5%) had cognitive impairment and, on an adjusted basis, were more likely to die (96.3% versus 68.2%. RR 2.19, 95% CI 1.41 to 3.39: P<0.001) and/or experience an unplanned hospitalization (100% versus 94%. RR 1.44, 95% CI 1.06 to 1.95: P=0.019). Cognitively impaired patients had a similar (non-significant) adjusted risk of death-or-readmission in both the CHF-MP (RR 1.40, 95% CI 0.63 to 3.11: P=0.403) and in usual care (RR 1.38, 95% CI 0.75 to 2.53: P=0.305). In the usual care cohort, cognitive impairment was associated with a greater (non-significant), adjusted risk of death (RR 1.61, 95% CI 1.10 to 4.92: P=0.122). In the CHF-MP, adjusted risk of death was significantly higher for cognitively impaired patients (RR 2.33, 95% CI 1.10 to 4.92: P=0.027).

Conclusion: These data suggest that "mild" cognitive impairment is of prognostic importance in CHF: even when a CHF-MP has been applied.

Key Words: Chronic heart failure • Cognitive impairment • Prognosis • Management

Received June 4, 2005; Revised September 3, 2005; Accepted November 10, 2005


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 References
 
In response to the significant burden imposed by large numbers of older, high-risk patients with chronic heart failure (CHF) on the hospital sector [1,2] there has been an increasing interest in developing and applying effective CHF-specific management programs (CHF-MPs). These programs employ a systematic but individualized approach to apply gold-standard pharmacotherapy and non-pharmacologic intervention strategies to optimize the management of this complex condition. Over the last decade more than 30 randomized trials of CHF-MPs have been conducted. Recent meta-analyses have confirmed their potential to reduce unacceptably high morbidity and mortality rates [3-6]. Worldwide, these programs have become part of the gold-standard management of CHF following acute hospitalization.

Despite the obvious benefits of applying CHF-MPs, data from these randomized studies show that even in patients exposed to optimal management, morbidity and mortality rates remain high. Clearly, some hospitalizations in CHF are unavoidable, and even desirable for clinical stabilization. Moreover, CHF is an inevitably fatal condition in most cases. However, anecdotal evidence suggests that there is some heterogeneity as to the impact of CHF-MPs on subsequent health care behaviors at an individual level. Distinguishing which patients gain the most (or least) benefit from these programs is highly desirable in order to either exclude poor responders for referral to better-tailored treatment, or to modify the interventions to better cater to high risk patients.

Given that CHF-MPs rely on enhancing patient self-care behaviors to improve health outcomes [7], one of the factors most likely to modulate the impact of CHF-MP's is cognitive impairment [8]. While dementia is the most extreme and well recognised form of cognitive impairment, less severe cognitive impairment can develop independently from dementia. Mild cognitive impairment can manifest as difficulties with memory, attention, concentration and/or problem solving. As such, even milder forms of cognitive impairment in CHF have the potential to impair an individual's ability to make a judgement call on seeking medical assistance and/or adhere to prescribed therapy in a safe and effective manner [9,10]. For example, it has been demonstrated that CHF patients with mild cognitive impairment identified using the Mini Mental Status Exam (MMSE) are less inclined or able to attend scheduled medical appointments [11].

Although it has been shown that more severe cognitive impairment is prognostically significant in CHF [12,13], there is minimal data examining whether less severe cognitive dysfunction is also prognostically important in this setting. The impact of mild cognitive impairment is of particular relevance to health care professions attempting to improve the management and outcomes associated with CHF, not only because of its high prevalence [8] and its potential to "blunt" the impact of otherwise effective CHF-MP's, but because unlike dementia, it is more likely to go undetected in the absence of systematic screening.

1.1. Study hypotheses
It is within this context that we prospectively tested the following null hypotheses in 200 typically elderly patients, without obvious signs of cognitive impairment at baseline (e.g. dementia) involved in randomized study of a home-based CHF-MP [14] followed-up for a prolonged period:

  1. There is no relationship between baseline cognitive function status (as determined by the MMSE [15]) and either long-term event-free survival or all-cause mortality when adjusting for potential confounders.
  2. If a relationship between cognitive function and health outcomes does exist, the CHF-MP will have the same effect on long-term health outcomes in patients with cognitive impairment (as defined by an MMSE score of ≤26) as it does on those with intact cognition.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 References
 
The current study involves the prolonged follow-up, and prospectively planned secondary analysis, of baseline data derived from a group of typically old patients with CHF, participating in a previously reported randomized controlled trial of a home-based CHF-MP [14].

2.1. Participants
As described in more detail previously [14], we consented and randomized 200 CHF patients recruited from a tertiary referral hospital in South Australia to either usual care or a multidisciplinary, home-based CHF-MP. The initial study with prolonged follow-up was approved by the institution's Ethics of Human Research Committee, and conformed to the principles outlined in the Declaration of Helsinki. Patients were eligible for inclusion in the study if they had a history of at least one admission for acute decompensated heart failure, a confirmed left ventricular ejection fraction of ≤55% as determined by echocardiography, and chronic exercise intolerance at hospital discharge defined as New York Heart Association (NYHA) Class II, III or IV. Alternatively, they were excluded if they had a terminal malignancy, a recorded diagnosis of dementia, or were not being discharged to their own home. It is important to note that in effect the combination of: (i) systematic, in-hospital screening for patients with dementia, conducted by a gerontology health care team, (ii) the need for informed consent directly from the patient and (iii) the active recruitment of patients being discharged to their own homes, predicated that the majority of patients would be assessed as being cognitively intact. As such, although we obtained MMSE scores from all patients at baseline, they were not used to exclude study involvement.

2.2. Baseline measures
2.2.1. Baseline clinical status
A comprehensive range of clinical, demographic and psychosocial variables (see Table 1) were collated through patient interviews and by reviewing medical records immediately prior to discharge [14]. A number of these variables deserve particular mention as they are of potential importance in the development of cognitive impairment. For example, a low left ventricular ejection fraction (LVEF) could potentially result in poor cerebral perfusion, and has been associated with poor cognitive performance in previous research [16], as have atrial fibrillation [17] and hypertension [18]. In addition, the cumulative load of serious comorbid illnesses, which was calculated using the Charlson Index of Comorbidity [19], may also impact on cognitive capacity.


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  		Table 1 Baseline characteristics of chronic heart failure patients according to cognitive status

 
2.2.2. Baseline cognitive function
Consistent with the pragmatic assessment of cognitive function in the clinical setting, baseline cognitive impairment was identified using the MMSE [15], which was administered just prior to hospital discharge (i.e. once subjects were judged to be clinically stable). The MMSE is a brief screening tool, which assesses aspects of short-term memory, orientation, concentration, and visuospatial skills. It provides an overall rating of global functioning ranging from 0 to 30, with higher scores indicating better performance [15]. A cut-off between 21 and 24 has traditionally been used to identify patients with probable dementia [20,21]. For the purposes of this study, we were interested in the effects of less severe impairment, and we therefore adopted a higher cut-off score of ≤26: a threshold still demonstrated to be of prognostic significance in less acutely ill cohorts [22]. As expected, only 7 patients (3.5%) recorded an MMSE score of 18-24 and, therefore, "probable dementia". A further 20 patients recorded an MMSE score of 25 and 26. Overall, therefore, a total of 27 patients (13.5%) were prospectively designated as "cognitively impaired".

2.2.3. Multidisciplinary, home-based intervention (CHF-MP)
As described in greater detail in the original report [14], patients in the intervention arm (n=100) received two visits by a specialist heart failure nurse in addition to the usual care administered through the hospital. During the first visit, which occurred prior to discharge, patients were counselled about compliance with their treatment regimen and the need to report any signs of clinical deterioration. A total of 89 patients consented to a second visit by the same nurse 7-10 days after discharge. Patients who withdrew their consent to be visited at home did not differ with respect to any clinical or demographic characteristics. During the second visit, an assessment was made of patients' knowledge of, and compliance with medications, and their available social supports. Patients demonstrating poor knowledge or compliance received tailored intervention involving one or more of the following: additional counselling and information, reminder aides, a flexible diuretic regimen and/or exercise program, referral to a community pharmacist, nurse and/or social worker for ongoing regular review. In addition, during this visit patients were examined for signs of clinical deterioration or adverse effects of prescribed medication. A detailed report and long-term plan was sent to all patients' primary care physicians and cardiologists. Additional telephone support, via patient-initiated calls and routine follow-up at 3 and 6 months was also provided. Repeat home visits were made for patients who survived an unplanned readmission within 6 months of their index hospitalization. Importantly, a low MMSE was not specifically used to tailor the study intervention.

2.3. Study follow-up and endpoints
All 200 patients were subject to 5-year follow-up (median 34 months, interquartile range 9 to 60 months, when taking into account fatal events) with censoring of all morbid and fatal events at July 31, 2004. All inpatient and outpatient hospital activity was monitored through the institution's computerized medical records system, individual case records, and contact with primary care physicians to determine the status of surviving patients. Official records of the time and location of all deaths in the region were used to compile mortality data.

2.4. Statistical analysis
Analysis was conducted in several stages. Initial univariate analyses were used to determine variables to be entered in multiple regression models (described below). Chi square tests were used for categorical data, Student t-tests for continuous variables and Mann-Whitney U-tests for non-normally distributed data. Step-wise, multiple-logistic regression analysis was then used to determine potential independent correlates of cognitive impairment (MMSE score≤26) with calculation of adjusted odds ratios (OR) and 95% confidence intervals (CIs).

Two unadjusted Kaplan Meier Survival Curves were initially constructed from actuarial life-tables of event-free survival and all-cause mortality and analysed with the log-rank and Breslow tests, respectively, to determine differences in the number and timing of events for patients with cognitive impairment relative to cognitively intact patients. Cox Proportional Hazards Models with adjusted relative risks (RR) and 95% CIs were also constructed (with entry of variables at a significance level of P<0.01 from initial univariate analysis and, if necessary, forced entry of cognitive impairment) in order to determine the potential independent correlates of all-cause mortality and event-free survival. Using the same methods, four additional adjusted survival curves were then generated to compare the all-cause mortality and event-free survival of patients with and without cognitive impairment on a treatment group-specific basis: separate survival curves generated for the usual care group and CHF-MP groups.

All analyses were performed with SPSS version 12.0 and on an intention-to-treat basis.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 References
 
3.1. Baseline characteristics
Table 1 (summary of baseline characteristics according to cognitive status) shows that this was a typically elderly cohort of patients with moderate to severe heart failure and significant comorbidity. Through randomization, 17 of the 27 patients with cognitive impairment were allocated to the CHF-MP arm of the trial, and 10 to usual care. Univariate analysis of baseline characteristics indicated that cognitively impaired patients were similar to cognitively intact patients with respect to all clinical and demographic variables except age and level of schooling: patients with cognitive impairment being significantly older (P<0.001) and less likely to have high school education (P<0.01). Multivariate analysis confirmed the independent correlation between cognitive impairment and advancing age (adjusted OR 1.12; 95% CI 1.04 to 1.20 per year: P=0.002) and less than 8 years of formal schooling (adjusted OR 4.89; 95% CI 1.33 to 17.1: P=0.017).

3.2. Cognitive status and long-term outcomes
3.2.1. Event-free survival
During 5-year follow-up, all 27 patients with cognitive impairment experienced an unplanned readmission or died within 42 months of their index hospitalization compared to 163 (94%) cognitively intact patients. Median event-free survival was 4 months (IQR 1 to 8) and 7 months (IQR 2 to 20), respectively, for the two groups (P=0.009). On an adjusted basis, the following variables were independently associated with a greater risk for this composite endpoint: greater comorbidity, more severe left ventricular systolic dysfunction and cognitive impairment. Conversely, those patients assigned to the CHF-MP and prescribed a beta-blocker at baseline were more likely to remain event free. Fig. 1 shows the unadjusted Kaplan Meier survival curves for event-free survival according to baseline cognitive status: the inset showing the results of the multivariate analysis. As such, those with cognitive impairment at baseline had a significant 1.4-fold increased risk of being admitted or dying relative to cognitively intact patients when adjusting for potential confounders (P=0.019).


Figure 1
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  		Fig. 1 Kaplan Meier survival curves for event-free survival: cognitively impaired versus cognitively intact patients.

 
3.2.2. All-cause mortality
During 5-year follow-up, 26 of 27 (96.3%) patients found to be cognitively impaired at baseline died, compared to 118 of 173 (68.2%) cognitively intact patients. Median survival times were 11 months (IQR 4 to 39) in subjects with cognitive impairment compared to 36 months (IQR 11 to 60) for the remainder of this patient cohort (P<0.001). On an adjusted basis, the following variables were independently associated with a greater risk of a fatal event: greater comorbidity, more severe left ventricular systolic dysfunction and impaired cognition. Once again, those patients assigned to the CHF-MP were more likely to survive to 5 years. Fig. 2 shows the unadjusted Kaplan Meier survival curves for all-cause mortality according to baseline cognitive status: the inset showing the results of the multivariate analysis. As such, those with cognitive impairment were more than two-fold more likely to die during study follow-up when adjusting for potential confounders (P<0.001).


Figure 2
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  		Fig. 2 Kaplan Meier survival curves for all-cause mortality: cognitively impaired versus cognitively intact patients.

 
3.3. Effect of the CHF-MP on health outcomes based on baseline cognitive status
Having established that cognitive function was independently associated with poor long-term outcomes, we then separately analysed the prognostic impact of cognitive impairment on long-term health outcomes in patients managed via the usual care and CHF-MP arms of the study.

3.3.1. Event-free survival
Fig. 3 shows the adjusted event-free survival curves (separate Cox Proportional Hazard Models) for the two treatment groups according to cognitive status. Curves from both analyses are plotted on the same axis. In both treatment groups, those with cognitive impairment appeared to fare worse (approximate 1.4-fold increased risk in both groups) than cognitively intact patients. Neither group-specific analysis found a significant relationship in this regard, most probably due to Type-II error. While group numbers were too small to allow for between-group statistical analyses, the adjusted event-free survival curves represented in Fig. 3 suggest that the beneficial effects of the CHF-MP were indeed "blunted" in those patients with cognitive impairment; their risk being similar to and even worse than those exposed to usual care.


Figure 3
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  		Fig. 3 Adjusted event-free survival curves for patients assigned to usual care (UC) or the CHF-MP based on cognitive status at baseline.

 
3.3.2. All-cause mortality
Fig. 4 shows the adjusted all-cause mortality curves (once again separate Cox Proportional Hazard Models) for the two treatment groups according to cognitive status. In both treatment groups, those with cognitive impairment appeared to fare worse than cognitively intact patients. In the CHF-MP treatment group, this relationship reached statistical significance. For patients in the CHF-MP, patients with cognitive impairment were more than two-fold more likely to die than their cognitively intact counterparts (P=0.027). Consistent with the pattern observed in relation to event-free survival, the adjusted survival curves represented in Fig. 4, not withstanding the non-significant within-group comparison, strongly suggest that the beneficial effects of the CHF-MP on survival were "blunted" in those patients with cognitive impairment; their risk of death being similar to and even worse than those exposed to usual care.


Figure 4
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  		Fig. 4 Adjusted all-cause mortality curves for patients assigned to usual care (UC) or the CHF-MP based on cognitive status at baseline.

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
References
 
Accumulating evidence indicates that a significant proportion of CHF patients suffer from cognitive impairment [8]. During prolonged follow-up, we found that patients who had mildly impaired cognition at baseline experienced significantly reduced event-free survival and overall life expectancy. Two large studies have previously reported higher mortality rates in CHF patients with cognitive impairment, however in both of these publications, only patients with severe cognitive impairment were included in analysis, and follow-up periods were limited to 12 months or less [12,13]. The results of this study suggest, for the first time, that even mild to moderate forms of cognitive impairment, which can be easily missed in the acute care setting, are predictive of negative clinical outcomes in typically elderly CHF patients over a prolonged period.

Further exploratory analysis focusing on the potential modulating effects of an otherwise beneficial home-based CHF-MP suggested that cognitively impaired patients failed to gain the same benefits in terms of prolonged event-free survival and, particularly, overall survival relative to cognitively intact patients: adjusted event rates for cognitively impaired patients in the CHF-MP group being similar to, or even worse than, those exposed to usual care. Once again this represents the first time such observations have been made.

Pending further research, the results of this study suggest that all CHF patients should be screened with a reliable but pragmatic screening tool such as the MMSE to detect even mild forms of cognitive impairment. Additional surveillance and long-term support should be carefully considered to decrease their risk of premature morbidity and mortality: clearly, this is usually the role of a CHF-MP. However, our additional analyses suggest that this broad approach may not be suitable for patients with even mild forms of cognitive impairment.

Why would patients exposed to this particular form of CHF-MP derive little or no benefit if suffering from cognitive impairment? Both the high mortality rates and the poor response to CHF-MP observed in patients with cognitive dysfunction could be related to a reduced capacity for self-care. The intervention model applied in this study, like other successful CHF-MPs, placed a heavy emphasis on providing patients with information and strategies aimed at increasing their capacity for self-management. Patients who had cognitive impairment may have been less able to comprehend and assimilate this information and/or less able to recall or implement strategies when changes in their condition occurred. Although no research to date has directly examined the effect of poor cognitive function on CHF patients' adherence to prescribed treatment regimens, adherence to both pharmacological and non-pharmacological interventions is low among CHF patients as a whole [23,24]. This may in part be a reflection of the high prevalence of cognitive dysfunction in the CHF population.

An alternative explanation for our results, both in terms of poor response to the CHF-MP and the higher rate of morbidity/mortality overall, is that impaired cognition is a strong, surrogate marker of disease progression or concurrent cerebrovascular disease, both of which lead to premature mortality. If patients with cognitive impairment are indeed suffering from a more severe phase of their illness, then even interventions that successfully improve self-management and adherence may have limited impact on subsequent health outcomes. Our results did not provide any specific support for this hypothesis. We failed to observe any associations between cognition and clinical indicators of disease severity. Findings from other research have been mixed. Some studies have reported modest relationships between cognitive impairment and symptom duration, LVEF, symptom severity, hemodynamic pressure variables and cardiovascular risk factors while others have failed to do so [8]. The available research data does not provide a conclusive explanation for the relationship between cognition and clinical outcomes, but it appears likely that physiological, cognitive and behavioral factors may interact in a cyclical manner to affect health outcomes.

In exploring possible explanations for the current findings, consideration must also be given to limitations of the study methodology, and in particular the way in which cognitive function was measured. The MMSE has been criticized because it lacks sensitivity in the detection of very mild forms of cognitive impairment [21]. An alternative approach to identifying and categorising low-level cognitive impairment might have been to apply the more rigorous diagnostic criteria for Mild Cognitive Impairment (MCI) currently used in clinical settings and epidemiological research to identify people who exhibit significant and measurable cognitive deficits, but do not meet diagnostic criteria for dementia [25]. Accurately diagnosing MCI according to this conceptualisation requires comprehensive neuropsychological and functional assessment. The MMSE was not designed for this purpose, and thus can only provide a general indication of cognitive capacity. To assist health care administrators who may be weighing the costs and benefits of a brief assessment using a screening tool such as the MMSE, against a more comprehensive examination, future research should investigate whether the more precise definition of MCI and the incorporation of more comprehensive assessment tools offer better predictive information.

In this study, older patients with less education were more frequently identified as cognitively impaired. A relationship between MMSE scores and age and education has been frequently reported in other research [20,21]. It is therefore possible that we mislabelled some older less educated subjects as cognitively impaired due to measurement bias. Analysis was complicated further because age and education also correlated with the outcome variables (mortality and event-free survival), raising the potential for confounding. However, we used regression analysis to test the independent effects of age, education and MMSE scores, and in each case MMSE scores proved to be a better predictor of morbidity/mortality than either age or education: even when forced into a model with these two variables mild cognitive impairment was still associated with a significant increased risk of suffering a hospitalization or death (RR 1.62, 95% CI 1.02 to 2.55: P=0.039) or death alone (RR 1.89, 95% CI 1.18 to 2.97: P=0.008).

During the study, we measured cognition only once and we do not know whether cognitive function improved or declined post-discharge. In all probability more patients developed cognitive dysfunction during 5-year follow-up, and these effects were not accounted for in our results. The extent of cognitive impairment was also lower than in comparable patient cohorts [8] with only 13.5% of our patients affected. This potential selection bias is likely to be a reflection of our exclusion of patients with a documented diagnosis of dementia, or who were to be discharged to institutional care or were clearly unable to consent to participate in the study. While the majority of studies in this area have included subjects more representative of the total CHF population, the subjects in this study cohort more accurately represent patients likely to be streamed to CHF-MPs.

Despite its limitations, this study has important clinical implications. Previously, cognitive impairment has been overlooked as an important factor in the clinical management of CHF. Results of this study indicate not only that CHF patients with even mild forms of cognitive impairment may be at increased risk of mortality and hospital readmission, but that CHF-MPs, a treatment model with substantial support for its efficacy, may not improve the prognosis of this high-risk group. Before recommendations for changes to clinical practice can be made, the results of this preliminary analysis need to be replicated in a prospective study using more sensitive neuropsychological measures of cognitive performance, and assessing additional clinical factors such as depression which may provide not only a better understanding of the aetiology of this condition, but also direction for effective treatment planning. Until better data on the aetiology, progression and mechanisms of impact of cognitive dysfunction are available, at the very least, all patients with CHF should be screened for cognitive impairment and, if present, should be reviewed carefully for more intensive management/surveillance with less reliance on promoting self-care activities to improve health outcomes.


   Acknowledgements
 
SS is supported by the National Heart Foundation and National Health and Medical Research Council of Australia.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 

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R. L.C. Vogels, P. Scheltens, J. M. Schroeder-Tanka, and H. C. Weinstein
Cognitive impairment in heart failure: A systematic review of the literature
Eur J Heart Fail, May 1, 2007; 9(5): 440 - 449.
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