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European Journal of Heart Failure 2006 8(8):856-863; doi:10.1016/j.ejheart.2006.02.008
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© 2006 European Society of Cardiology

Effect of socioeconomic deprivation on the population risk of incident heart failure hospitalisation: An analysis of the Renfrew/Paisley Study

S. Stewarta, N.F. Murphyb, J.J.V. McMurrayb,*, P. Jhundb,c, C.L. Hartc and D. Holec

a Division of Health Sciences, University of South Australia and Faculty of Health Sciences, University of Queensland Australia
b Department of Cardiology Western Infirmary, Scotland, UK
c Public Health and Health Policy, University of Glasgow Scotland, UK

* Corresponding author. Department of Cardiology, Western Infirmary, Glasgow G12 8QQ, Scotland, UK. Tel.: +44 1412111838; fax: +44 1412112252. E-mail address: j.mcmurray{at}bio.gla.ac.uk


   Abstract
Top
 Abstract
1. Introduction
 2. Study hypothesis
 3. Methods
 4. Results
 5. Discussion
 References
 
Background: There are few data describing the effect of socioeconomic deprivation on the risk of developing heart failure (HF).

Aims: To examine the relationship between socioeconomic deprivation and hospitalisation with HF over 20 years.

Methods: Between 1972 and 1976, 15,402 individuals, aged 45–64 years, residing in two towns in Scotland, underwent cardiovascular screening. We report hospitalisations with HF over the subsequent 20 years according to Carstairs deprivation category and Social Class.

Results: Following screening, 628 men and women (4.1%) were hospitalised with a primary diagnosis of HF. There was a gradient in the risk of HF hospitalisation with increasing socioeconomic deprivation (P=0.003). Of the most deprived individuals, 6.4% were hospitalised for HF compared to 3.5% of the most affluent group. Cox-proportional Hazard models showed that independent of age, sex and baseline risk factors for cardio-respiratory status, greater socioeconomic deprivation increased the risk of HF admission (P=0.001, overall). The adjusted risk of admission for HF was 39% greater in the most versus least deprived subjects (RR 1.39 95% CI 1.04–2.01; P=0.04).

Conclusion: These data show a link between social deprivation and the risk of developing HF, irrespective of baseline cardio-respiratory status and cardiovascular risk factors.

Key Words: Heart failure • Morbidity • Epidemiology

Received September 12, 2005; Revised January 3, 2006; Accepted February 13, 2006


   1. Introduction
Top
 Abstract
 1. Introduction
2. Study hypothesis
 3. Methods
 4. Results
 5. Discussion
 References
 
Although the adverse effect of socioeconomic deprivation on cardiovascular health in general is well known [1-3], there are few studies specifically describing the influence of deprivation on heart failure [4]. Socioeconomic deprivation is associated with a higher prevalence of heart failure [5], worse functional class and quality of life [6,7], higher rates of hospital admission (and re-admission) [8-10] and poorer survival in patients with this syndrome [11]. The effect of socioeconomic deprivation on the long-term risk of developing heart failure is, however, unknown. Consequently, we have examined the relationship between socioeconomic deprivation and a subsequent admission to hospital for heart failure over a 20-year period in a large cohort of middle-aged men and women initially enrolled in the one of the largest epidemiologic studies ever undertaken—the Renfrew/Paisley Study.


   2. Study hypothesis
Top
 Abstract
 1. Introduction
 2. Study hypothesis
3. Methods
 4. Results
 5. Discussion
 References
 
We prospectively hypothesised that the baseline socioeconomic status of subjects participating in the Renfrew/Paisley Study, as measured by a composite and individual index of the same, would be an independent determinant of risk for heart failure morbidity during 20-year follow-up.


   3. Methods
Top
 Abstract
 1. Introduction
 2. Study hypothesis
 3. Methods
4. Results
 5. Discussion
 References
 
Renfrew and Paisley are two adjacent urban areas located west of the city of Glasgow and the River Clyde, in the West of Scotland. In the 20th Century shipbuilding and heavy engineering industries thrived and provided a rich source of employment for the local community—particularly manual labour. In the 1970s just under 115,000 people resided in these two towns; approximately 17% were aged between 45 and 64 years. Between 1972 and 1976, 7048 men and 8354 women, representing 80% of subjects in this age group, took part in the Renfrew/Paisley Study—one of the largest epidemiologic studies ever undertaken [12].

Written consent was given at this time for hospital records to be subsequently monitored. Ethical permission was obtained from Argyll and Clyde LREC for linkage with the Scottish Morbidity Records system. The study was approved by the Privacy Advisory Committee of the Information and Statistics Division, Scotland and, therefore, conforms with the principles outlined in the Declaration of Helsinki.

3.1. Baseline data
During original screening of this population cohort, each subject's demographic profile and cardio-respiratory health status were documented. Angina pectoris (classified as none, possible or definite by the Rose Angina questionnaire [13]) and chronic bronchitis (determined by the Medical Research Council's Chronic Bronchitis questionnaire [14]) were specifically sought. Past and current medical history and risk factors for cardio-respiratory disease were also documented. Blood pressure, height and weight (used to calculate body mass index in kg/m2) were measured using standardised methods. Chest radiography and vitalography were also undertaken and cardiothoracic ratio and forced expiratory volume in one second (FEV1) calculated. Cardiomegaly was defined as a cardiothoracic ratio of ≥0.55. An adjusted FEV1 score was calculated as a percentage of the "expected" FEV1 score (derived from a linear regression equation of age and height for men and women separately from a healthy subset of the population who were both non-smokers and had no respiratory symptoms) and the actual FEV1 score [15]. Plasma cholesterol and glucose concentration were measured in a non-fasting blood sample. A six-lead electrocardiograph (ECG) was also obtained and Minnesota coded [16]. Within the constraints of limited ECG leads (the lack of precordial leads would limit the detection of S-T changes indicative of anterior myocardial ischaemia and definitive ECG changes indicative of underlying left ventricular hypertrophy), these data were used to identify the presence of underlying left bundle branch block, S-T segment changes indicative of underlying myocardial ischaemia and left ventricular hypertrophy in addition to arrhythmias such as atrial fibrillation.

3.2. Socioeconomic deprivation
A total of 15,370 participants (99.8% of the total cohort) had a documented postcode of residence that was used to determine their socioeconomic status based on the Carstairs-Morris Deprivation category. This index, based on official Scottish-wide census data, can be used to rank postcodes of residence into seven deprivation categories (1 = least, 7 = most deprived) according to levels of employment, living conditions, car ownership and social class [17]. It is important to note there are 1010 postcode sectors in Scotland, identified by a combination of the first five characters of the postcode (representing 937 areas) and the Council Area. The average population is 5012 (range 51 people to 20,512). Although there are smaller geographical units for "small area analysis" (e.g. data zones and output areas), the 1981 and 1991 Carstairs indices are only available for postcode sectors and study analyses applied in this study adhere to recognized methods for their use in this context. (http://www.isdscotland.org/isd/info3.jsp: accessed December 2005). Data on the social class of subjects, determined by regular occupation at baseline screening according to the Registrar General's classification [18], was also collated in a smaller proportion of the study cohort (n=14,983 or 97.3% of the total cohort with a lack of specific data for 350 predominantly female subjects). Women's social class was based on their own occupation except when they stated housewife, in which case their husband's occupation was used. The Registrar General's classification was: I Professional etc. occupations, II Managerial and technical occupations, IIIN Skilled non-manual occupations, IIIM Skilled manual occupations, IV Partly-skilled occupations and V Unskilled occupations.

Preliminary analyses indicated that the Carstairs-Morris Deprivation category was most sensitive to subsequent heart failure-related outcomes and, combined with its availability in a larger number of cases, was used as the main indicator of socioeconomic deprivation in reported analyses. In order to test the validity and robustness of this composite index of social deprivation and specifically examine this parameter on an individual basis, we also examined study outcomes according to Social Class.

3.3. Heart failure-related admission to hospital
Scotland has a National Health Service (NHS) offering universal and free health-care to all citizens. Virtually all health-care (especially emergency care and that relating to chronic illness) is delivered in NHS hospitals. The Scottish Morbidity Record Scheme [19] was, therefore, used to retrieve details of all hospital discharges (according to the Eighth [a small number of initial episodes] and Ninth revisions of the World Health Organisation International Classification of Diseases [20]) over the 20 years after initial screening as previously described [11,21]. Surviving subjects were, therefore, aged 65-84 years at the end of study follow-up. The following ICD 9 (and equivalent ICD 8) codes were used to determine the presence of heart failure: 402 (hypertensive heart failure), 425.4 (primary cardiomyopathy), 425.5 (alcoholic cardiomyopathy), 425.9 (secondary cardiomyopathy), 428.0 (congestive heart failure), 428.1 (left heart failure) and 428.9 (heart failure, unspecified). A recent validation of ICD coding of each hospital discharge in Scotland suggests that diagnostic data are 90% accurate overall [22].

3.4. Statistical analysis
We firstly compared the baseline risk factor profile for future cardiovascular events according to socioeconomic status using {chi}2 analyses and analysis of variance with post hoc testing of multiple comparisons, where appropriate. All morbidity (heart failure admissions) and mortality data were censored for surviving subjects at 20 years post-screening with determination and censoring of events according to the month of follow-up. Initial Kaplan Meier survival curves were constructed from actual life-tables to compare the unadjusted risk of a subsequent heart failure hospitalisation according to Carstairs-Morris Deprivation category and individual Social Class. These data were analysed with the log-rank and Breslow tests, respectively, to determine differences in the number and timing of events.

To delineate the independent contribution of socioeconomic status (Carstairs-Morris deprivation category only) to subsequent heart failure admission, Cox proportional hazards models were constructed by inclusion of blood pressure, body mass index, non-fasting serum cholesterol and blood sugar level, past history of stroke or myocardial infarction, symptoms suggestive of a transient ischaemic attack or angina, cardiomegaly, left bundle branch block or ischaemia on electrocardiography, adjusted FEV1 score, and presence of bronchitis and also Social Class: all continuous variables were entered into these models unchanged. A backward, step-wise process was used to reject all variables, with the exception of deprivation category, associated with a P value (two-tailed) of <0.1. An initial model examined the combined effect of socioeconomic deprivation on the risk of heart failure admission in men and women combined. As sex was found to be an independent predictor of such an event, separate models were then constructed to confirm a similar trend according to socioeconomic status. For each categorical variable in the model (e.g. deprivation category), the lowest class was set at unity and all adjusted RR and 95% CI are relative to this class unless otherwise stated. Where there were a limited data (specifically non-fasting blood sugar levels) separate models were constructed in their presence and absence to determine adjusted RR. SPPS version 11.0 was used for all analyses.


   4. Results
Top
 Abstract
 1. Introduction
 2. Study hypothesis
 3. Methods
 4. Results
5. Discussion
 References
 
4.1. Baseline risk
Of the 15,370 men and women from the Renfrew/Paisley Study cohort included in this analysis, 967 were classified as the "most affluent" (deprivation category = 1) and 627 as "most deprived" (deprivation category = 7) according to their original postcode of residence. Table 1, shows that overall, there appeared to be a marked gradient in the overall cardiovascular risk factor profile of both men and women in this study cohort according to their baseline socioeconomic status. In both sexes, there was a significant trend for those in the most deprived categories to have a past history of myocardial infarction and a past or current smoking habit, self-reported symptoms indicative of transient ischaemic cerebral attacks and cardiomegaly as demonstrated by their chest radiography. In women only, there was a significant trend for more deprived individuals to have a left bundle branch block on their ECG, a past stroke and to be obese. In men only, deprived individuals were significantly more likely to have higher non-fasting blood sugar levels (when recorded). There were no statistical differences across the deprivation categories according to systolic and diastolic blood pressure, presence of ECG changes indicative of myocardial ischaemia and "definite angina" as determined by the Rose Angina Questionnaire.


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  		Table 1 Comparison of baseline cardiovascular risk factor profile according to deprivation category

 
4.2. Subsequent heart failure hospitalisations
During 20 years of follow-up, a total of 628 men and women in this study cohort were hospitalised with a primary diagnosis of heart failure (4.1% overall).

Figs. 1 and 2 show the unadjusted Kaplan Meier survival curves for the cumulative risk of hospitalisation for heart failure during the 20-year follow-up according to baseline Carstairs-Morris Deprivation category (n=15,370) and Social Class (n=14,983), with censoring according to duration of survival during the 20-year follow-up.


Figure 1
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  		Fig. 1 Cumulative risk of heart failure admission based on Carstairs-Morris Deprivation category (1 = least deprived, 7 = most deprived). There were no cases classified as Category 2 based on residential postcode.

 


Figure 2
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  		Fig. 2 Cumulative risk of heart failure admission based on individual Social Class — Registrar General's classification: I Professional etc. occupations, II Managerial and technical occupations, IIIN Skilled non-manual occupations, IIIM Skilled manual occupations, IV Partly-skilled occupations and V Unskilled occupations.

 
Using the Carstairs-Morris deprivation categories, there was a statistically significant gradient in the risk of such an event according to socioeconomic status (Log rank test: P=0.003). As shown in Fig. 1, 6.4% of the most deprived individuals (category 7) were hospitalised for heart failure during the 20-year follow-up, compared to 3.5% of the more affluent individuals (deprivation categories 1, 3 and 4). Those in deprivation categories 5 (4.2%) and 6 (4.7%) had an intermediate rate of admission. This trend was evident in both men and women.

A smaller and more polarised, trend was also evident on the basis of individual Social Class when recorded: around 5% versus 4% of individuals predominantly working in lower paid (manual) versus higher paid ("white collar") jobs (Fig. 2).

4.3. Adjusted risk according to baseline socioeconomic status
Cox proportional hazards models showed that worse socioeconomic status at baseline was associated with a higher risk of subsequent heart failure hospitalisation independent of age, sex and baseline risk factors for cardiovascular disease (including systolic and diastolic blood pressure and smoking status) and various indicators of pre-existing cardiovascular disease (P<0.001, overall). Table 2 shows the final Cox proportional hazards models for men and women separately and then combined. Overall, the risk of admission for heart failure in the most deprived cohort was approximately 40% greater than in the most affluent cohort (RR 1.39 95% CI 1.04-2.01; P=0.044), after adjusting for age, sex and baseline cardiovascular risk factors. On a sex-specific basis, this risk appeared to be greater in men than women (64% versus 53% increased risk), although the specific comparison between the most and least deprived category in either sex did not reach significance. There was however a significant trend across the different deprivation categories indicating a greater risk of a heart failure admission with increasing deprivation in both men (P=0.028) and women (P=0.041).


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  		Table 2 Independent predictors of a heart failure admission within 20 years of baseline screening

 
4.4. Outcomes in initially healthy subjects
At study baseline there were approximately 2500 "healthy" subjects who had no signs and symptoms of cardiovascular disease and did not exhibit any of the major modifiable risk factors for heart disease. A comparison of the most affluent (deprivation categories 1 and 2) versus the most deprived (categories 6 and 7) of these subjects revealed that the latter were close to five times more likely to be admitted for heart failure during study follow-up with 2 of 251 subjects (0.8%) versus 26 of 682 (3.8%) subjects admitted, respectively, during the subsequent 20-year follow-up: P=0.016, OR 4.93, 95% CI 1.16 to 20.9.


   5. Discussion
Top
 Abstract
 1. Introduction
 2. Study hypothesis
 3. Methods
 4. Results
 5. Discussion
References
 
This study adds new information about the role played by socioeconomic deprivation in cardiovascular disease in general and unique information concerning its specific effects on the risk of developing heart failure in the longer-term. Though socioeconomic factors have been convincingly shown to influence symptomatic status and fatal and non-fatal outcomes in patients with an existing diagnosis of heart failure, it was not known whether deprivation also increased the risk of developing new heart failure [4-11].

The present study and another recent one from our group [5] now indicate that socioeconomic deprivation does indeed increase the risk of incident heart failure. This excess risk is clearly related, in part, to the worse risk profile identified at initial screening in the more deprived subjects in the current study. The most deprived individuals in this population cohort were undoubtedly more likely to be un-employed or employed as an unskilled manual labourer. Their cardiovascular risk profile overall showed that compared to more affluent individuals and regardless of socioeconomic factors, they were more likely to develop subsequent cardiovascular disease and heart failure in particular. However, despite extensive adjustment for these baseline imbalances, deprivation was still associated with a 40% increase in the risk of admission to hospital with heart failure. Significantly, even those deprived individuals found to be in good cardiovascular health at baseline, were more than four times more likely to subsequently develop heart failure relative to equivalently healthy and more affluent individuals.

It could be argued that any analysis of hospital admissions might exaggerate the effect of social deprivation by reflecting both a true increase in incidence and a greater likelihood of hospitalisation (as opposed to outpatient/primary care treatment); particularly as socially deprived patients are more likely to seek hospital care [23]. However, in a recent study of consultations with primary-care physicians, we found an almost identical increase in the adjusted risk of incident presentation with heart failure in relation to deprivation [5].

Why should socioeconomic deprivation increase the incidence of heart failure? The explanation is undoubtedly likely to be complex. The clinical syndrome of heart failure occurs at the end of a chain of clinical events and reflects a number of different underlying aetiologies/patho-physiological processes. The most common of these are left ventricular systolic and diastolic dysfunction. The damaging effects of myocardial infarction, hypertension or both, usually cause left ventricular dysfunction. Assuming our multivariable analysis fully adjusted for the baseline imbalances in the precursors of heart failure, there are still multiple other ways in which socioeconomic deprivation might increase the risk of developing this syndrome. The rate of treatment with (and adherence to) anti-hypertensive therapy and anti-infarction treatments (e.g. antiplatelet drugs, statins) may be less in more deprived individuals [24-28]. Socioeconomic deprivation is also associated with later presentation of infarction (with less opportunity for myocardial salvage) [29,30], more heart failure at the time of infarction [31-33], more co-morbidity (such as diabetes) [30,33] associated with a higher risk of subsequent heart failure and less use of secondary preventive treatments (and revascularisation) [30,32,33]. Smoking rates after infarction are also higher in deprived groups and, interestingly, smoking was associated with a significantly greater risk of incident heart failure hospitalisation in the Prevention arm of the Studies Of Left Ventricular Dysfunction (SOLVD-P) [33,34].

In other words, socioeconomic deprivation may interact at multiple points along the "chain of events" from behaviours and risk factors known to promote the development of coronary disease and hypertension right through to the treatment of these conditions, the subsequent likelihood of their causing myocardial damage, the extent of the damage that develops, the use of interventions to limit this and prevent further cardiac injury and finally, behaviours (and perhaps other factors) promoting progression of myocardial damage already sustained. The fact that our composite index of social deprivation was a more powerful predictor of heart failure-related outcomes than individual Social Class suggests that external factors do play an important part in the "chain of events" that lead to heart failure. The cluster of events around the most deprived individuals suggests that they have been exposed to a unique, but as yet unknown, set of circumstances that has resulted in their risk of developing heart failure markedly increasing relative to less deprived individuals. Clearly, this requires further investigation.

This study does have some important limitations that require comment. We predominantly relied upon a geographic (postcode) rather than individual indicator of socioeconomic status for the major analyses. However, many studies that utilize postcodes have been shown to be useful measures of deprivation and our analysis of the more limited data relating to individual Social Class was generally supportive of our main findings. Our hospital discharge database does not contain information on cardiac structure and function. We could not, therefore, determine what specific type of heart failure subjects were admitted with. Nor can we definitively confirm a correct diagnosis in each case. While it is possible that the type of heart failure (for example alcoholic cardiomyopathy) might have varied across the deprivation categories, there were no discernible differences in this regard. Moreover, the aim of our study was to look at the overall burden of heart failure, realising that hospital admission for any type of heart failure has sinister prognostic implications. Because the importance of heart failure was under-recognised in the 1970s and not sought specifically during screening we do not have baseline data on this condition. However, this was a relatively healthy cohort and, as reported previously [21], there were very few individuals who reported dyspnoea on exertion and nearly all of these fulfilled the MRC's criteria for chronic bronchitis. Overall, only 53 HF admissions (7.7% of the total) occurred within two years of initial screening. Overall, these data indicate that the vast majority of subjects were heart failure-free at baseline. We were also unable to serially measure the risk factor profile of subjects over time, relying on baseline data only in this regard and cannot fully account for potential confounders for the observed "independent" effects of deprivation on long-term cardiovascular outcomes.

In summary, we have shown that socioeconomic deprivation is a strong and independent predictor of the future development of heart failure. Strategies to limit the growing and costly "epidemic" of heart failure need to examine issues beyond traditional indices of health and take account of socioeconomic factors that undoubtedly play an important role in not only its development but also its prognostic impact.


   Acknowledgements
 
SS is supported by the NHMRC of Australia and the NHF of Australia, NM is funded by the British Heart Foundation.


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

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