 
|
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Journal of the New Zealand Medical Association,
21-April-2006, Vol 119 No 1232
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Estimated prevalence of cardiovascular disease and
distribution of cardiovascular risk in New Zealanders: data for healthcare
planners, funders, and providers
Susan Wells, Joanna Broad, Rod Jackson
Cardiovascular disease (CVD) is the leading cause of death
and hospitalisation in New Zealand.1 There are major disparities in CVD between
ethnic groups and significant under-treatment of high-risk patients.
Age-specific death rates are two to three times higher for Maori compared with
non-Maori in those aged less than 75 years.2 CVD prevention and management and
the reduction of health inequalities have been targeted as priorities in
the New Zealand Health Strategy, He Korowai
Oranga (Maori Health Strategy), and
Primary Health Care Strategy.
Current New Zealand CVD risk management guidelines recommend
targeting CVD risk assessment to all men aged over age 45 years and women aged
over 55 years (10 years earlier for people of Maori, Pacific Island, or Indian
ethnicity or if they have known CVD risk factors or are at high risk of
developing diabetes3 [Appendix 1]).
Treatment recommendations are based primarily on the
patient’s estimated absolute risk, with pharmacological treatments
recommended for those over 15% 5-year absolute CVD risk.
To inform their health-needs assessments, and to guide
healthcare planning and funding decisions, over the previous 2 years we have
been asked by district health boards (DHBs) and primary healthcare organisations
(PHOs) to provide estimates of the prevalence of CVD and distributions of
CVD-risk in the community. As there is limited data on CVD and absolute risk
prevalence available in the public domain, we considered that this information
would also be useful to other DHBs and PHOs.
MethodsPopulation estimates were provided by Statistics New
Zealand for the projected 2005 adult population aged over 35 years (divided
according to 5-year age groups and gender) for the whole of New Zealand, and for
each DHB separately. Estimates were based on the 2001 Census usually resident
populations, assuming medium fertility, medium mortality, and medium migration
term projection methods.
To calculate absolute CVD risk, we used data from the
Auckland Heart and Health Study (AHAH)4 to estimate the proportion eligible for
risk assessment and to derive estimates of the prevalence of existing
cardiovascular disease and cardiovascular risk factors.
The AHAH study was a population-based cross-sectional
survey conducted between 1993 and 1994. The study population included 2507 men
and women aged 35–84 years and resident within the Auckland region of New
Zealand.
Age-stratified samples were randomly chosen from
central Auckland general electoral rolls with a response rate of
72%. The investigators aimed to include
250 subjects from each 10-year age/sex category. For our purposes, data were
reaggregated into 5-year age/sex categories.
Analyses excluded Maori and Pacific Island ethnic
groups as the sampling frame did not include the Maori electoral roll and the
general electoral rolls significantly under-represented the true proportions of
Pacific and Maori peoples within the general population. A detailed account of
AHAH study methodology is presented elsewhere.4
The proportion eligible for risk assessment was based
as closely as possible to the New Zealand Guideline Criteria (Appendix 1). Data on personal history of gestational
diabetes, polycystic ovarian syndrome, known impaired glucose tolerance or
impaired fasting glycaemia, and waist circumference were not available. However
these omissions are unlikely to add significantly to the number of eligible
people.
Previous history of CVD in the AHAH study includes
coronary heart disease and previous self-reported stroke—but not transient
ischaemic attack, peripheral vascular disease, or previous coronary artery
surgery. Coronary heart disease was determined by self-reported myocardial
infarction, with hospital admission or angina defined as currently taking
nitrate medication. The AHAH study did not collect any data on CVD ‘risk
equivalents’ (genetic lipid disorders or diabetes with nephropathy).
The absolute CVD risk over a 5-year period for each
individual was estimated using a risk prediction model based on the Framingham
Heart Study.5 The model includes gender, age, systolic blood pressure, smoking,
total cholesterol:high density lipoprotein (TC:HDL) ratio, diabetes, and
interaction terms of age by gender, and diabetes by gender. A cardiovascular
event is defined in the risk prediction model as a death related to coronary
disease, non-fatal myocardial infarction, new angina, fatal or non-fatal stroke,
or transient ischaemic attack—or the development of congestive heart
failure or peripheral vascular disease.
Summary measures of risk categories (proportion over
20%, 15–20%, 10–15%, and less than 10% absolute CVD risk) were
obtained for each 5-year age-gender group.
For the small number of people (1.5%) missing blood
pressure or lipid data we calculated their absolute risk using the age/gender
specific median value for that risk factor. Rate smoothing via moving averages
was applied to better reflect the naturally occurring patterns within
populations and all estimated counts were rounded.
To estimate the numbers of people meeting
risk-assessment criteria (as defined in the guideline),3 we used:
ResultsOf the projected 2.09 million people aged over 35 years in
New Zealand in 2005, approximately 1.5 million (72%) would meet national
criteria for formal CVD risk assessment. Table 1 shows the proportion of New
Zealanders over 35 years with prior CVD and the distribution of absolute CVD
risk in those without prior CVD, by gender and 5-year age group for the
estimated 2005 population.
Approximately 151,000 people (7%) have suffered a heart
attack or stroke or have angina (or a combination of these). About 272,000
people (13%) are at high (CVD risk 15–20%) or very high (CVD risk over
20%) risk of a new CVD event in the next 5 years. Men are about three times as
likely to be at high or very high risk than women (19% vs 7%). A further 10% of
the total population over the age of 35 years are at moderate risk (CVD risk
10–15% in 5 years).
For each DHB catchment, aggregated estimates of CVD
prevalence and CVD risk distributions are shown (Table 2). The proportion of
people aged over 35 years meeting criteria for drug treatment (with prior CVD or
an absolute CVD risk over 15% in 5 years) varies from 18.3% to 25.5% according
to the demographic structure of the DHB.
DiscussionCurrent New Zealand guidelines for the management of CVD
risk are based on evidence demonstrating that the magnitude of benefit from
treatment for an individual patient is directly proportional to their
pre-treatment absolute CVD risk.6 Those who have had a prior CVD event and those
at high risk of having a first event have the most to gain from identification
and coordinated care. In appropriately targeted patients, the New Zealand
guidelines suggest that 55% of future CVD events could be prevented.3 We
estimate that 7 out of 10 New Zealanders over 35 years of age should have a
baseline risk assessment; and of those risk-assessed people, 1 out of 5 would
meet criteria for drug treatment.
Cardiovascular risk prediction based on the Framingham Heart
Study5 is integral to the New Zealand cardiovascular risk assessment and
management guidelines. The Framingham Heart Study was a cohort of mainly white
Americans living in Massachusetts, USA in the 1970s and 1980s. The resultant
cardiovascular risk prediction equation has been found to accurately predict on
a population basis the 5-year risk of hospitalisation or death from a first
cardiovascular event in New Zealand men aged 35 to 74 years and women aged 35 to
69 years.7
Extrapolating data collected over 10 years ago from 2507
Aucklanders to the New Zealand population in 2005 requires caution. However they
are the only currently available data and are given as ‘ball park’
estimates only. Our findings may underestimate the true prevalence of CVD in New
Zealand as they are based on a study that did not include Maori and Pacific
people who have higher risk of CVD. Furthermore, these estimates do not include
those who have had a sole diagnosis of other cardiovascular disease including
transient ischaemic attack, acute coronary syndrome, percutaneous coronary
intervention (PCI), or peripheral vascular disease. However, many people with
these diagnoses will have other manifestations of atherosclerotic disease. For
example, studies of patients presenting with intermittent claudication indicate
that around 50% have evidence of coronary disease on clinical history and
ECG,8,9 (and 90% have coronary disease angiographically10).
Nevertheless, the magnitude of the reported CVD risk burden
is likely to be reasonable because the effect of excluding Maori and Pacific
people, and some CVD diagnoses will be offset by declining secular trends in CVD
morbidity and mortality over the previous 10 years.2
Despite the limitations of the data, this aggregate
information is much needed by PHOs and DHBs to guide service planning and health
care delivery particularly with new funding streams (for example the CarePlus
programme) and requirements to fulfil key quality indicators for their
population’s health. The major challenge for primary care is to
systematically identify those people most at risk and to ensure they are
appropriately managed. If this occurs, the potential to reduce this leading
cause of mortality and morbidity in New Zealand, while also reducing disparities
between ethnic and socioeconomic groups, will be substantial.
Author information:
Susan Wells, Senior Lecturer – Clinical Epidemiology; Joanna Broad,
Epidemiologist; Rod Jackson, Professor of Epidemiology; Section of Epidemiology
and Biostatistics, School of Population Health, University of Auckland,
Auckland
Acknowledgements:
The Auckland Heart and Health Study was funded by the Health Research Council
and the National Heart Foundation while Dr Wells is the recipient of a National
Heart Foundation Research Fellowship. We also thank Elizabeth Robinson and
Patricia Metcalf for their helpful comments and feedback.
Correspondence:
Dr Susan Wells, Section of Epidemiology and Biostatistics, School of Population
Health, University of Auckland, Private Bag 92019, Auckland 1. Fax: (09) 373
7494; email: s.wells@auckland.ac.nz
References:
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| | Current
issue | Search journal |
Archived issues | Classifieds
| Hotline (free ads) Subscribe | Contribute | Advertise | Contact Us | Copyright | Other Journals |
|