Journal of the New Zealand Medical Association, 29-June-2012, Vol 125 No 1357
The most deprived Auckland City Hospital patients (2005–2009) are 10 years younger and have a 50% increased mortality following discharge from a cardiac or vascular admission when compared to the least deprived patients
Chris Ellis, Andie Pryce, Garth MacLeod, Greg Gamble
Patients admitted to a public hospital should have the same access to investigations and treatment regardless of their socioeconomic status and thus anticipate similar outcomes. Equity is a stated aim of the New Zealand Medical Association.1 However, for nearly all causes of death in New Zealand large socioeconomic mortality gradients have been reported.2 Inequities have been observed in clinical management of acute coronary syndrome patients in hospitals with and without invasive facilities.3,4
The long-term intervention with pravastatin (LIPID) trial showed that in both Australia and New Zealand increased mortality was associated with decreased income, a marker for socioeconomic status in patients.5 These findings may have been exacerbated by poor health delivery structures with sparse clinical (doctor and nursing) input into management.6
Heart failure hospitalisations and death also increase with increasing deprivation in New Zealand.7 In New Zealand, Canada, England and the United States of America, analyses of national statistics showed worsening health care indicators in the most deprived compared with the least deprived quintile of socioeconomic status.8
We examined how medium to long-term patient outcomes may be affected by social deprivation following hospital discharge. It has been previously stated that New Zealand needs to consider the totality of information to manage its health system effectively9. However to date no descriptive data have been published on patient outcome following a cardiac or vascular discharge from a New Zealand hospital. Further, a descriptive audit of post discharge mortality in relation to admission deprivation level is lacking.
We aimed to describe the 30 day and 1 year mortality of any cardiac or vascular discharge in adult patients (age ≥15 years). We also planned to compare the mortality rates of these patients, by deprivation index (after adjustment for age and gender).
Study design and subjects—The study population comprised all patients resident within the ADHB region aged 15 years or more discharged from an Auckland District Health Board (ADHB) hospital between 1 July 2005 and 31 December 2009 with a cardiac or vascular diagnosis related group (DRG)10 (Appendix 1). Each of these patients was matched for subsequent events to 1 June 2010.
The study was judged by expedited review by the North Health Ethics committee to be an audit and therefore approved without further review. The definition of an admission is that the patient had been in hospital at least three hours after being seen by a doctor or the patient had a procedure. If two or more admissions were present within the audit period the first admission was counted as the index admission.
Each patient hospital discharge is coded and categorised into a DRG which classifies admissions according to the resources consumed.10 DRGs are assigned on the basis of the International Classification of Diseases (ICD) diagnoses,11 procedures, age, gender, discharge status, and the presence of complications and/or comorbidities.
Within the discipline of cardiology there are 67 DRGs which, for the purposes of aggregating numbers, can be amalgamated further into: acute coronary syndrome (ACS)/circulatory management, congestive heart failure (CHF), electrophysiology (EP), general cardiology, cardiac surgery and peripheral vascular disease (PVD) management.
During the audit period each unique patient contributed an index (i.e. first) admission and the date of a second (and number of subsequent) readmission(s) to any ADHB hospital. Patients with an index admission were matched against the national death register and the date of death and the cause of death integrated.
The domicile code for each patient was obtained from the hospital information system and was linked to the New Zealand Deprivation 2006 (NZDep2006) Index.12 Socioeconomic status was then reported as decile of deprivation from 1 (least deprived) to 10 (most deprived). The NZDep2006 is a small area index of deprivation that provides a score for each mesh block in New Zealand based on nine variables (material and social domains of deprivation) from the 2006 Census.12 The NZ Deprivation Index is more strongly correlated with cardiovascular disease and diabetes than the NZSEI or income.13,14
In official statistics “prioritised ethnicity” is assigned as Māori15 if one of the three possible self-identified ethnicity responses was Māori. This represents the total Māori ethnic group. For those not allocated as Māori, the person is assigned as Pacific Island ethnic group if one of the self-identified ethnic groups was Pacific Island ethnic group, then Asian if an Asian ethnic group is recorded. Residual patients are then classified as European or ‘other’ ethnicities. Since the Indian ethnic group comprised a significant proportion of the ‘Asian’ ethnic groups these data have been presented separately from the ‘Asian’ category in this paper.
Statistics—Data were summarised as rates and 95% confidence intervals. Logistic regression was used to make comparisons after adjustment for age, gender and ethnicity and the results are presented as odds ratios and 95% confidence intervals. Cox proportional hazards models (with adjustment for age, gender and ethnicity) were used to compare survival time amongst the groups of interest.
Results were presented as hazard ratios (with 95% confidence intervals) and the proportionality assumption was tested. Tests of linear trend were performed using orthogonal contrasts for normally distributed tests and the Cochran-Armitage test for ordinal data. All analyses and data manipulations were performed using SAS statistical software (SAS Institute Inc, v 9.2). Patient years were calculated for each patient as the time from index admission to the end of follow-up or death. Events per patient year were calculated using OpenEpi (www.openepi.com All tests were two-tailed and P<0.05 was considered statistically significant.
These data show that when compared to the least deprived patients, the most deprived patients are 10 years younger and have a 50% age and gender-adjusted increased mortality following discharge from a cardiac or vascular admission to Auckland City Hospital in 2005–2009.
Unadjusted data—From 1 July 2005 to 31December 2009 there were 19,545 cardiac patient discharges from patients resident in the Auckland District Health Board (ADHB) region. Most (50%) were related to acute coronary syndrome or circulatory management, 30% were classified as ‘general cardiology’ with small proportions (<10% each) categorised as CHF, EP, cardiac surgery or PVD management (Table 1).
Overall, the numbers of cardiac discharges were similarly spread across the NZDep Index ranging from 18 to 23% (P=0.87, Table 1). However, those patients discharged following cardiac surgery showed increasing proportions of discharges from more deprived patients (P=0.037). In contrast the number of patients discharged following EP management showed increasing proportions from less deprived patients (P=0.04, Table 1).
All-cause mortality following a hospital discharge over a median 2.4 years follow-up was 6.2 deaths per 100 patient years follow-up (Table 1). Unadjusted mortality was higher (6.9 deaths/100 patient years) in those attributed to the least deprived category in comparison with the most deprived category (5.7 deaths/100 patient years) (P<0.05, Table 1) . However, the most deprived patients tended to be 10 years younger than the least deprived (57 years vs 66 years P<0.0001), and were more likely to be male (55% v 50%, P<0.0043, Table 2).
The average age at discharge was 61 years (SD 19) (Table 2). All-cause unadjusted mortality was highest for those following a CHF discharge (28 deaths/100 patient years) and lowest following ACS and circulatory management discharge (4.1 deaths/100 patient years) (Table 1).
The proportion of European ethnicity decreased and the proportions of patients with prioritised Māori or Pacific Island ethnicity increased with increasing deprivation (P<0.0001) (Table 2). The most deprived patients had a significantly longer length of stay, (on average one day more P<0.0001) and they had more diagnoses reported at discharge (P<0.0001) which is a simple surrogate for patients who are more unwell with more comorbidities (Table 2).
Across categories of unadjusted deprivation there were no differences in the in-hospital death rates (overall 1.8%, P=0.23), or death at 30 days (overall 3% P=0.075) or at 1 year (overall 8.1%, P=0.40) after a cardiac discharge (Table 3). However, by a median follow-up of 2.4 years, unadjusted least deprived patients had a greater mortality (but were approximately 10 years older). Increasing deprivation was associated with increased readmission rates (Table 3).
Table 3. Readmissions to an Auckland District Health Board hospital until 1 June 2010
Note: All-cause death to 1 March 2009 (unadjusted data). Outcome following any cardiac discharge 1 July 2005 to 31 December 2009 in Auckland District Health Board Residents aged 15 years and over.
[(-) indicates trend for decreasing number with increasing deprivation (+) indicates trend for increasing number with increasing deprivation.]
Depr: Deprived; FU: Follow-up; Readmiss: Readmission [to hospital].
The characteristics of patients discharged following ACS and circulatory management show a similar pattern to the entire cardiac cohort: deprived patients are younger, more likely to be male and to have a larger proportion of patients of Māori or Pacific Island origin (Table 4). They also had increased number of discharge diagnoses (a crude measure of co-morbidities) and longer length of stay (Table 4).
Table 4 “ACS and Circulatory Management” diagnosis-related group discharges 1 July 2005 to 31 December 2009 in ADHB residents aged 15 years and over (unadjusted data).
Note: [see Appendix for acute coronary syndrome/invasive management 20 Diagnosis Related Group codes).
(-)indicates trend for decreasing number with increasing deprivation (+)indicates trend for increasing number with increasing deprivation.]
LOS: Length of stay; SD: Standard deviation; IQR: Interquartile range.
There are no differences in deaths following ACS and circulatory management admissions across deprivation levels using the unadjusted data however the number of readmissions increases with worsening deprivation (Table 5).
Table 5. Readmissions to an Auckland District Health Board hospital until 1 June 2010. (All-cause death to 1 March 2009 (unadjusted data) for acute coronary syndrome/circulatory diagnoses.)
Note: Outcome following an acute coronary syndrome/circulatory management cardiac discharge 1 July 2005 to 31 December 2009 in Auckland District Health Board Residents aged 15 years and over. [(-)indicates trend for decreasing number with increasing deprivation (+)indicates trend for increasing number with increasing deprivation.]
Adjusted data—From the unadjusted data it is seen that the most deprived patients are 10 years (57 v 66 years, P<0.0001) younger and males are more frequently (54% v 50% P<0.0001) admitted in the most deprived group. Therefore to assess overall mortality over time the data needs to be age and gender adjusted to fully assess the impact of deprivation.15
Figure 1 shows the age and gender adjusted risk estimates of death, and the composite death/readmission for each NZDep Index level, compared to the least deprived group. Throughout the follow up, death at 1 year and at 2.4 years of follow-up, and the composite endpoint of death/readmission, were significantly increased (all P<0.0001) in the most deprived NZ Dep Index: category 9-10 compared with the least deprived NZ Dep Index: category 1-2. For these endpoints the trend was a linear increase across the groups.
Figure 1 also shows that short term 30-day mortality has a similar pattern, with mortality increasing with increasing levels of deprivation, however the confidence intervals were wide and the trend failed to reach conventional statistical significance. The same pattern was apparent for an analysis restricted to acute coronary syndrome/circulatory management patient admissions (Figure 2).
Figure 1. Mortality after any cardiac admission (all 67 cardiac Diagnosis Related Groups see Appendix 1) to an Auckland District Health Board hospital by deprivation index. (Age and gender adjusted data.)
Figure 2. Mortality after an acute coronary syndrome/circulatory management admission (20 Diagnosis Related Group categories see Appendix 1) to Auckland City Hospital. (Age and gender adjusted data.)
Cox proportional hazards modelling was performed for time to all-cause death at a median follow up of 2.4 years after a cardiac admission and adjusted for age and gender (Figure 3A) and with additional adjustment for ethnicity (Figure 3B).
Figure 3A. Age/Gender adjusted hazard of all cause mortality after a cardiac admission to Auckland City Hospital
Figure 3B. Age/Gender/Ethnicity adjusted hazard of all cause mortality after a cardiac admission to Auckland City Hospital
Adjusting for age, gender, ethnicity and length of stay attenuated the result slightly however increasing deprivation remained significantly associated with increased mortality (NZ DepI 1-2 HR=1, NZ DepI 2-3 HR=1.08 (1.0,1.2) P=0.18, NZDep I 4-6 HR=1.14 (1.0, 1.3) P=0.02, NZDepI 6-8 HR=1.15 (1.0,1.3) P=0.02, NZDep I 8-10 HR=1.20 (1.01, 1.08) P<0.0001).
Similar modelling was performed for an ACS and circulatory management admission and adjusting for age, gender (Figure 4A) and additionally for ethnicity (Figure 4B). Overall, and for those with ACS and circulatory management discharges the same pattern was seen, a statistically significant increase in risk of early death with increasing deprivation. Adjustment for ethnicity, in addition to age and gender did not change this observation.
Unadjusted all-cause mortality was higher at a median follow up of 2.4 years (17%) in the least deprived group (NZDep 1-2) compared with the most deprived group (NZDep 9–10) (14%) (P=0.0018, Table 6).
Table 6. All-cause mortality at a median follow-up of 2.4 years by ethnic group in the least deprived and most deprived groups
There were no differences in all-cause age/gender adjusted mortality across ethnic groups for those in the least deprived group however in those classed most deprived, Māori and Pacific people were at increased risk of age/gender adjusted death compared to Europeans following cardiac discharge whilst Asians were at reduced risk (Table 6).
In comparison to least deprived (NZDep 1-2) Europeans, the most deprived (NZDep 9–10) Europeans, Māori and Pacifica peoples had significantly increased age and gender adjusted all-cause mortality (Figure 5).
Overall, men had a 20% age-adjusted increased risk of all-cause death at a median follow-up of 2.4 years compared with women (HR 1.2 (95%CI 1.14–1.32, P<0.0001) and the risk of all-cause mortality increased with increasing deprivation in both men and women (Figure 6).
When considering the age of the patient (Figure 7), the association with deprivation was most pronounced in those aged <60 years with increasing risk of gender adjusted death with increasing level of deprivation (p=0.0063 for trend across first to last Dep levels).
In patients aged 60 to 75 years the association was present, but less pronounced (p=0.0006 across Dep levels). In those aged > 75 years there was no association between risk of all-cause death and worsening deprivation (p=0.096 across Dep levels, Figure 7). These data suggest that deprivation is associated with a marked shortening of life in younger age groups.
Figure 4A. Age/Gender adjusted hazard of all cause mortality after an acute coronary syndrome or circulatory management admission to Auckland City Hospital
Figure 4B. Age/Gender/Ethnicity adjusted hazard of all cause mortality after an acute coronary syndrome or circulatory management admission to Auckland City Hospital
Figure 5. Age/gender adjusted risk of all cause death in those most (New Zealand Deprivation Index 9-10) and least deprived (New Zealand Deprivation Index 1–2) by ethnic origin (data are hazard ratio 95%CI). P is for comparison against referent group (least deprived Europeans).
Figure 6. All-cause mortality for men and women by New Zealand Deprivation Index (overall age adjusted) for men compared to women is 1.2 (95% CI1.14, 1.32) P<0.0001.
Figure 7 All cause mortality for men and women by New Zealand Deprivation Index (overall gender adjusted) for those aged > 75, 60-65 and < 60 at discharge.
About 8% of all discharges from an Auckland District Heath Board hospital are cardiac or vascular, comprising roughly equal proportions of people across the categories of the NZ Deprivation Index. About half of all cardiac or vascular admissions are for “acute coronary syndrome and circulatory management”.
Overall, subsequent mortality is low (6.2 deaths /100 patient years). Patients who were most deprived were 10 years younger than those who were least deprived and more likely to be male. Hence, although fewer deaths are observed in those who are most deprived (5.7 deaths/100 patient years) than in those who are least deprived (6.9 deaths /100 patient years), an age and gender adjustment is clearly needed, and then the overall risk of all-cause mortality over a median 2.4 years follow-up is 50% greater for those most deprived in comparison with the least deprived group.
Previous studies have shown large socioeconomic mortality gradients exist for nearly all causes of deaths in the New Zealand community.2 The New Zealand census-mortality study examined age and ethnicity standardised mortality for 25-94 years. They compared NZ deprivation index groups 9 and 10 (most deprived) with groups 1 and 2 (least deprived).
All-cause mortality was 2.0 (1.9, 2.2) for men and 2.1 (1.9, 2.3) for women. Cardiovascular disease rate ratios were 2.4 (2.1, 2.8) for men and 2.4 (2.0, 3.0) for women.16 The same pattern persists in these data, in patients following a cardiac or vascular admission to Auckland City Hospital.
More Māori and Pacific Islands people are likely to be classified as most deprived. After adjustment for this imbalance, a consistent linear increase in risk of early death is still seen with increasing levels of deprivation, suggesting that deprivation results in a worse outcome independent of ethnicity.
When a patient’s ethnicity is considered, in patients identified as least deprived there is no difference in age and gender adjusted all-cause mortality across ethnic groups. However in the most deprived patients, Māori and Pacific Islands people have significantly increased mortality compared to similarly deprived European patients. Asian patients tend to have reduced all-cause mortality compared to Europeans.
This observation suggests an added risk for those of Māori or Pacific Islands ethnicity in those who are most deprived. This may reflect barriers to primary or secondary healthcare services which might prevent or delay acute hospital admissions, and/or failures of primary screening.
Marked ethnic and socioeconomic disparities in the prevalence of cardiovascular disease in New Zealand has been shown in a 2006-2007 cohort.17
Māori had the highest age-standardised prevalence compared to the rest. Prevalence of cardiovascular disease increased with increasing deprevation.17 Deprivation is also known to be associated with increased risk of heart failure death or heart failure admission which has been shown to be worse overall for Māori.7
There are several possible reasons for the more deprived having a worse outcome. First, there may be differences at presentation. At presentation more deprived patients may have more (or more severe) comorbid conditions, or may delay their presentation to hospital or may have experienced less effective primary care.
Younger patients presenting to the coronary care unit at Middlemore Hospital have a worse cardiovascular risk profile, and are more likely to be obese, to smoke, to have low HDL and high triglyceride levels.18 However Malcolm19 found that in 127,426 primary health organisation (PHO) patients that Māori actually had better access to cardiology inpatient services than non-Māori.
Further, the New Zealand Acute Coronary Syndrome Audit of 2002 showed that in-patient management was a reflection of geographical location and service provision, and not of ethnicity.2
Second, there may be different treatment of patients during their inpatient admission as it is possible that treatment within hospital differs by socioeconomic status, although this seems unlikely. Supporting data for the absence of a treatment bias within the hospital might come from the survival curves from these data.
Early deaths are not split by deprivation; it is late deaths that are driving this effect. Hence the comprehensive public practice within a hospital may be unbiased, but after hospital discharge, the ongoing medical effects of socioeconomic deprivation are seen.
Third, there may also be differences with pre-hospital deaths, outpatient follow-up, or patient adherence to appropriate lifestyle or medication, or a range of other unknown differences.
The differences in access to treatment are more likely to be greater between hospitals than within a hospital and may present as a socioeconomic difference when the hospital supports a lower SES demographic. Ellis et al have shown that patients are less likely to receive interventional cardiology if they don’t present to an interventional centre. Non-interventional centres are more likely to be rural and poor.3
These data also suggest that deprivation is associated with a marked shortening of life in younger age groups after a cardiac or vascular admission. It is unclear why the effect of deprivation is not seen in the older age groups. Possible reasons include: the younger more deprived members have already died; older patients may live in less deprived suburbs, and since the NZ Deprivation Index is driven by address, some older patients may be misclassified as they may have now a standard income: the pension, the same as with people from ‘more deprived’ people, and therefore may be less able to access extra assistance e.g. private health care which could result in better outcomes with earlier assessment and management of medical problems.
There are a number of potential limitations for this study including the relatively small number of Māori or Pacific Islands people in the lower deprivation categories, a focus on all-cause mortality, reliance on information extracted from the official admissions record (which has no information on the severity of casemix at presentation) and using patients self-reported (but verified) address to model socioeconomic status, as a few individuals may have been misclassified by providing incorrect address information.
Whilst the external validity (generalisability) of these conclusions is unchanged, since these represent an analysis of official statistics for a large number of consecutive admissions at a major tertiary hospital, the conclusion must be tempered by the understanding that the internal validity might be reduced by confounding factors.
Socioeconomic deprivation is associated with earlier age at presentation and a markedly increased chance of death and hospitalisation following discharge from a cardiac or vascular related admission to a public hospital in New Zealand. These data are of considerable concern and highlight the clear need to develop and implement comprehensive strategies to improve on this health inequality within the New Zealand health care environment.
Competing interests: None known.
Author information: Chris Ellis, Cardiologist , Green Lane CVS Service, Cardiology Department, Auckland City Hospital, Auckland; Andie Pryce, Clinical Analyst, Auckland City Hospital, Auckland; Garth MacLeod, House Officer, Auckland City Hospital. Auckland; Greg Gamble, Statistician, University of Auckland
Correspondence: Dr Chris Ellis, Cardiology Department, Green Lane CVS Service, Level 3, Auckland City Hospital, Grafton, Auckland 1023, New Zealand. Email: email@example.com
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