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European Journal of Heart Failure 2006 8(2):203-207; doi:10.1016/j.ejheart.2005.03.008
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© 2006 European Society of Cardiology

Predictors of exercise capacity and everyday activity in older heart failure patients

Miles D. Withama,*, Ishbel S. Argoa, Derek W. Johnstonb, Allan D. Struthersc and Marion E.T. McMurdoa

a Section of Ageing and Health, University of Dundee, Ninewells Hospital Dundee DD1 9SY, UK
b School of Psychology, University of Aberdeen Aberdeen, UK
c Department of Clinical Pharmacology, University of Dundee, Ninewells Hospital Dundee DD1 9SY, UK

* Corresponding author. Tel.: +44 1382 632436; fax: +44 1382 660675. E-mail address: m.witham{at}dundee.ac.uk


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 
Background: Exercise capacity and daily activity are key outcomes for older, frail heart failure patients. Little is known about the determinants of these outcomes in this patient group.

Aims: To explore predictors of exercise capacity and daily activity in older, frail heart failure patients.

Methods: Analysis of prospectively collected data from a cohort of 82 patients aged 70 years and over, enrolled in a randomised controlled trial of exercise in heart failure patients. Pathophysiological, demographic, psychological and social factors were analysed by multivariate regression to determine predictors of exercise capacity (6-min walk distance) and daily activity (daily accelerometer counts).

Results: Between 49% and 55% of the variance in 6-min walk distance was explained by variables including New York Heart Association class, depression score, attitude to ageing and use of walking aids. Only 11% to 26% of the variance in accelerometer scores was explained by the model; 6-min walk distance was the only consistent predictor of daily activity.

Conclusions: Physical, psychological and attitudinal variables contribute to variance of the 6-min walk. Six-minute walk distance predicts a small amount of the variance in daily activity, but the majority of variance in daily activity remains unexplained and requires further investigation.

Key Words: Aged • Heart failure Congestive • Exercise capacity • Daily activity

Received October 4, 2004; Accepted March 3, 2005


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 References
 
Heart failure is a leading cause of hospitalisation and death. Even in patients who remain in the community, heart failure is associated with severe impairment of exercise capacity, functional ability and health-related quality of life. Physical function, as measured by both exercise capacity and daily activity, is limited in patients with heart failure [1-4], and improving physical function is an important goal of heart failure therapy in its own right, independent of the prognostic power that these indices carry [5,6]. This is arguably even more the case in older, frail patients, where limited life expectancy due to comorbid disease renders quality of life relatively more important than quantity of life. Whilst a number of therapies have been shown to improve exercise capacity in older patients with heart failure [1,7,8], daily activity appears to be more difficult to influence [9-12].

Previous studies have suggested that factors such as symptoms, muscle strength, maximal oxygen uptake and psychological status can influence 6-min walk distance [13-15]. There is little comparable data on the determinants of everyday activity in heart failure [4,16]; the available evidence suggests that physical and attitudinal factors may partly determine daily activity. Most studies of heart failure are done on comparatively young patients, often of working age, who usually lack significant comorbid disease. Many studies are done on highly selected subgroups of patients, e.g. those attending transplant centres awaiting cardiac transplantation. Findings regarding physical function and daily activity in such patients may not be translatable to typical older, frail heart failure patients with multiple comorbidities [17,18]. A better understanding of the factors that help determine exercise capacity and daily activity in older heart failure sufferers should therefore assist with the design of therapeutic strategies for use in this patient group. We investigated the contribution of a wide range of psychological, demographic, physical and disease variables to baseline exercise capacity and everyday activity in a cohort of older, frail heart failure patients recruited to a randomised controlled trial.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 References
 
Patients were recruited into a randomised controlled trial of seated exercise training for chronic heart failure. Patients were recruited from the local heart failure clinic and from the local Medicine for the Elderly clinic. Inclusion criteria were: age 70 years or above, diagnosis of chronic heart failure according to the European Society of Cardiology guidelines, LV systolic dysfunction confirmed by echocardiography, contrast ventriculography or radionuclide ventriculography, and New York Heart Association (NYHA) class II or III symptoms. Exclusion criteria were: unstable angina, history of sustained ventricular tachycardia or ventricular fibrillation, unable to mobilise independently, aortic stenosis with peak gradient >30 mm Hg, atrial fibrillation with ventricular rate of >100, abbreviated mental test score <6/10. The study conformed with the principles outlined in the Declaration of Helsinki, and was approved by Tayside Local Research Ethics Committee. All participants gave written informed consent.

All subjects underwent a baseline assessment comprising a detailed history and physical examination. Left ventricular function was ascertained by examining routine clinical echocardiography reports, which classify function as normal, mildly impaired, moderately impaired or severely impaired on the basis of visual assessment supplemented by fractional shortening measurement in selected cases. Carstairs deprivation scores were obtained from standard tables using the postal code of the patient [19]. Daily activity over a 7-day period was measured at baseline, 3 months and 6 months using the Stayhealthy RT3 accelerometer (Stayhealthy, Monrovia, USA), which has previously been validated in older, frail patients [20]. Six-minute walk test [21], Hospital Anxiety and Depression score (HADS) [22], and Philadelphia Geriatric Morale score (PGMS) [23] were performed at baseline, 3 and 6 months. Data were stored on a database and analysed using SPSS version 11.5.

It is difficult to ascertain whether factors that correlate with exercise capacity or daily activity are merely associated, are determinants, or are determined by these measures. By constructing putative models of factors that may be determinants of exercise capacity and daily activity, logically unlikely associations can be discarded. Factors for analysis were selected only if they were likely to play a causal, rather than merely an associative role, in determining exercise capacity or daily activity. Thus for exercise capacity, factors representing symptoms, muscle dysfunction, environment, psychological factors and comorbid disease were selected. For everyday activity, social, psychological, environmental factors, along with comorbid disease, exercise capacity and symptoms were selected. At each timepoint, 6-min walk distance and accelerometry counts were compared with possible predictive factors using univariate regression analysis. Factors showing a significant correlation with the 6-min walk distance or with accelerometry readings (p<0.05) were entered into a stepwise multivariate regression analysis.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 References
 
Two hundred and twenty-six patients were eligible for inclusion in the randomised controlled study; of these, 85 patients consented to enter the study. Eighty-two patients underwent a full baseline assessment and were subsequently randomised to one of the study groups. Data on these 82 patients is presented in Table 1. Significant univariate correlates of 6-min walk distance and accelerometry readings at baseline, 3 and 6 months are given in Table 2, and Table 3 shows the results of entering these significant correlates into a multivariate regression analysis.


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  		Table 1 Baseline details

 


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  		Table 2 Predictors of 6-min walk distance and accelerometry on univariate analysis

 


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  		Table 3 Predictors on multivariate analysis (p<0.05 in, p<0.1 out, stepwise linear regression)

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
References
 
Exercise capacity and everyday activity are important clinical outcomes in any chronic disease, especially for older, frail patients in whom prolongation of life may not always be the primary aim of therapy. Improvements in these measures should therefore be seen as a goal of therapy, rather than merely a surrogate for modifying the underlying disease. Previous work examining the determinants of exercise capacity in chronic heart failure has not included very old, frail patients with multiple comorbidities, and there is little previous work examining the determinants of everyday activity in heart failure [4,10,16,24].

The patients enrolled into the randomised controlled trial from which this data was obtained are much older than is usually in studies of heart failure (mean age 80 years). These patients had severely impaired exercise capacity as measured by the 6-min walk, a heavy burden of comorbid disease, and severe functional impairment. The patients in this study are thus typical of those seen in everyday clinical practice [18].

Our data suggest that in older people with heart failure, exercise capacity as measured by the 6-min walk test is explained by the use of walking aids (a marker of physical disability), age, smoking and symptom severity (as denoted by the NYHA class) but also by psychosocial factors, as denoted by the HADS depression score, and attitudinal factors, denoted by the PGMS attitude to ageing score. In combination, these factors explained 50-60% of the variance in the 6-min walk distance—a similar figure to that found in a general population of retirement village residents [25]. We found no evidence that the severity of LV dysfunction predicted exercise capacity; this is in line with previous findings [26,27].

The variance in everyday activity as measured by accelerometer counts is much less well explained by the factors measured in this study—only 26% of the variance was explained at best, and the factors correlating with accelerometer counts were much less stable over time than those correlating with the 6-min walk distance. Nevertheless, exercise capacity as measured by the 6-min walk test did correlate with accelerometry readings. Correlation between the 6-min walk test and daily activity has been noted in some, but not all previous works [9,24,28]. What is perhaps more noteworthy is the lack of a consistent correlation between accelerometry counts and measures of symptoms and signs of heart failure, such as NYHA class. This suggests that daily activity in heart failure is not simply limited by symptoms, reinforcing previous evidence that some patients with heart failure perform daily activity well below their exercise capacity [4]. This suggests that a more complex set of factors underlies the variance in daily activity. Psychological factors including depression, attitudes and beliefs might be expected to play a part; there is evidence from one previous study that higher self-efficacy ratings predict higher daily activity [16], but neither the HADS scores nor the PGMS scores entered the final multivariate model to explain daily activity in our study. There was no correlation between which group patients were randomised to and either exercise capacity or accelerometry on univariate analysis at any timepoint.

Caution is necessary in interpreting these results. Association does not imply causation, and for many of the significant associations that we have found, there is probably a reciprocal relationship. Impaired psychosocial status for instance may well impair performance of the 6-min walk test, but impaired exercise capacity would be expected to lead to low mood, social withdrawal and impaired psychosocial status. Cross-sectional studies such as this one cannot explain causation. A larger study with greater statistical power may have allowed a wider range of factors to reach significance in the models; the absence of a factor in the final model should not be taken to mean that it has no effect on exercise or daily activity.

Our results suggest that if we are to successfully improve exercise capacity and everyday activity in older heart failure patients, we need a better understanding of the factors underpinning these outcomes, as a large proportion of the variance remains unexplained. The application of therapies directed towards improving psychological parameters in heart failure may be a worthwhile additional strategy to improve exercise ability however. Further work is needed to explore novel factors that may influence daily activity.


   Acknowledgements
 
With thanks to the participants and to the staff of the Royal Victoria Day Hospital.

Funding: Funding for this study was provided by The Health Foundation (formerly PPP Health Foundation), grant number 2006/918. We confirm that the conduct of the study, analysis and publication of the results are independent of the study funders.


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

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