Validation of ICD-10-AM Coding for Myocardial Infarction Subtype in Hospitalisation Data.

BACKGROUND: International Classification of Disease (ICD) codes are central for identifying myocardial infarction (MI) in administrative hospitalisation data, however validation of MI subtype codes is limited. We measured the sensitivity and specificity of ICD-10-AM (Australian Modification) codes for ST-elevation MI (STEMI) and non-STEMI (NSTEMI). METHODS: A sample of MI admissions was obtained from a dataset containing all MI hospitalisations in Western Australia (WA) for 2003, 2008 and 2013. Clinical data were collected from hospital medical records (n=799 patients). Cases were classified by ICD-10-AM codes for STEMI, NSTEMI and unspecified MI, and compared to clinical classification from review of available electrocardiographs (ECGs) and cardiac biomarkers (n=660). Sensitivity and specificity for ICD-10-AM coding versus clinical classification was measured, stratified by calendar year of discharge. RESULTS: The majority of classifiable cases had MI recorded in the principal diagnosis field (STEMI n=293, 84.2%; NSTEMI n=202, 74.3%; unspecified MI n=20, 50.0%). Overall sensitivity of the ICD-10-AM STEMI code was 86.3% (95% CI 81.7-90.0%) and was higher when restricted to MI as a principal versus secondary diagnosis (88.8% vs 66.7%). Comparable values for NSTEMI were 66.7% (95% CI 61.5-71.6%), and 68.8% vs 61.4% respectively. Between 2003 and 2013, sensitivity for both MI subtypes increased: 80.2-89.5% for STEMI, and 51.2-73.8% for NSTEMI. Specificity was high for NSTEMI throughout (88.2% 95% CI 84.1-91.6%), although improving over time for STEMI (68.1-76.4%). CONCLUSIONS: The sensitivity and specificity of ICD-10-AM codes for MI subtypes in hospitalisation data are generally high, particularly for principal diagnosis cases. However, the temporal improvement in sensitivity in coding of MI subtypes, particularly NSTEMI, may necessitate modification to trend studies using administrative hospitalisation data.

Validation study of GRACE risk scores in indigenous and non-indigenous patients hospitalized with acute coronary syndrome.

BACKGROUND: Although cardiovascular disease is the major cause of premature death among Indigenous peoples in several advanced economies, no acute coronary syndrome (ACS) risk models have been validated in Indigenous populations. We tested the validity and calibration of three Global Registry of Acute Coronary Events (GRACE) scores among Aboriginal and non-Aboriginal Australians. METHODS: GRACE scores were calculated at admission or discharge using clinical data, with all-cause deaths obtained from data linkage. Scores for GRACE models were validated for; 1) in-hospital death, 2) death within 6 months from admission or 3) death within 6 months of discharge (this also for 1 and 5-years mortality). RESULTS: Aboriginal patient were younger (62 % aged <55 years versus 15 % non-Aboriginal) and their median GRACE scores lower than non-Aboriginal patients, as was crude mortality at 6 months from admission (6 % vs 10 %) and at 1 and 5 years. After age stratification, risk scores for Aboriginal patients were equivalent or higher, especially among those aged <55 years. There was a trend to more deaths after discharge among Aboriginal patients in each age group, suggesting an age-related under-estimation of risk. The c-statistics for the three GRACE models within both groups were between 0.75 and 0.79. CONCLUSIONS: We demonstrated for the first time that while the discriminatory capacity of GRACE risk scores among Indigenous Australians is good, the models may need re-calibrating to improve risk stratification in this and other Indigenous groups, where age of onset of coronary disease is much younger than among the original reference population.

Disparities experienced by Aboriginal compared to non-Aboriginal metropolitan Western Australians in receiving coronary angiography following acute ischaemic heart disease: the impact of age and comorbidities.

INTRODUCTION: Aboriginal Australians have a substantially higher frequency of ischaemic heart disease (IHD) events than their non-Aboriginal counterparts, together with a higher prevalence of comorbidities. The pattern of health service provision for IHD suggests inequitable delivery of important diagnostic procedures. Published data on disparities in IHD management among Aboriginal Australians are conflicting, and the role of comorbidities has not been adequately delineated. We compared the profiles of Aboriginal and non-Aboriginal patients in the metropolitan area undergoing emergency IHD admissions at Western Australian metropolitan hospitals, and investigated the determinants of receiving coronary angiography. METHODS: Person-linked administrative hospital and mortality records were used to identify 28-day survivors of IHD emergency admission events (n =20,816) commencing at metropolitan hospitals in 2005-09. The outcome measure was receipt of angiography. The Aboriginal to non-Aboriginal risk ratio (RR) was estimated from a multivariable Poisson log-linear regression model with allowance for multiple IHD events in individuals. The subgroup of myocardial infarction (MI) events was modelled separately. RESULTS: Compared with their non-Aboriginal counterparts, Aboriginal IHD patients were younger and more likely to have comorbidities. In the age- and sex-adjusted model, Aboriginal patients were less likely than others to receive angiography (RRIHD 0.77, 95% CI 0.72-0.83; RRMI 0.81, 95% CI 0.75-0.87) but in the full multivariable model this disparity was accounted for by comorbidities as well as IHD category and MI subtype, and private health insurance (RRIHD 0.95, 95% CI 0.89-1.01; RRMI 0.94, 95% CI 0.88-1.01). When stratified by age groups, this disparity was not significant in the 25-54 year age group (RRMI 0.95, 95% CI 0.88-1.02) but was significant in the 55-84 year age group (RRMI 0.88, 95% CI 0.77-0.99). CONCLUSIONS: The disproportionate under-management of older Aboriginal IHD patients is of particular concern. Regardless of age, the disparity between Aboriginal and non-Aboriginal Australians in receiving angiography for acute IHD in a metropolitan setting is mediated substantially by comorbidities. This constellation of health problems is a 'double-whammy' for Aboriginal people, predisposing them to IHD and also adversely impacting on their receipt of angiography. Further research should investigate how older age and comorbidities influence clinical decision making in this context.

Transfers to metropolitan hospitals and coronary angiography for rural Aboriginal and non-Aboriginal patients with acute ischaemic heart disease in Western Australia.

BACKGROUND: Aboriginal people have a disproportionately higher incidence rate of ischaemic heart disease (IHD) than non-Aboriginal people. The findings on Aboriginal disparity in receiving coronary artery procedures are inconclusive. We describe the profile and transfers of IHD patients admitted to rural hospitals as emergency admissions and investigate determinants of transfers and coronary angiography. METHODS: Person-linked hospital and mortality records were used to identify 28-day survivors of IHD events commencing at rural hospitals in Western Australia. Outcome measures were receipt of coronary angiography, transfer to a metropolitan hospital, and coronary angiography if transferred to a metropolitan hospital. RESULTS: Compared to non-Aboriginal patients, Aboriginal patients with IHD were more likely to be younger, have more co-morbidities, reside remotely, but less likely to have private insurance. After adjusting for demographic characteristics, Aboriginal people with MI were less likely to be transferred to a metropolitan hospital, and if transferred were less likely to receive coronary angiography. These disparities were not significant after adjusting for comorbidities and private insurance. In the full multivariate model age, comorbidities and private insurance were adversely associated with transfer to a metropolitan hospital and coronary angiography. CONCLUSION: Disparity in receiving coronary angiography following emergency admission for IHD to rural hospitals is mediated through the lower likelihood of being transferred to metropolitan hospitals where this procedure is performed. The likelihood of a transfer is increased if the patient has private insurance, however, rural Aboriginal people have a lower rate of private insurance than their non-Aboriginal counterparts. Health practitioners and policy makers can continue to claim that they treat Aboriginal and non-Aboriginal people alike based upon clinical indications, as private insurance is acting as a filter to reduce rural residents accessing interventional cardiology. If health practitioners and policy makers are truly committed to reducing health disparities, they must reflect upon the broader systems in which disparity is perpetuated and work towards a systems improvement.

Use and long-term outcomes of implantable cardioverter-defibrillators, 1990 to 2009.

BACKGROUND: Automated implantable cardioverter-defibrillators (ICDs) have become standard therapy for patients at high risk for sudden cardiac death. Linked data allow examination of trends in use and long-term survival after ICD implantation in an adult population. METHODS: Linked state-wide person-based data on hospital admissions and deaths from 1980 to 2009 were used to identify incident cases of ICD implantation. Population rates were calculated using census data. Kaplan-Meier techniques were used to describe cumulative survival. Cox regression models were used to determine the factors associated with the outcomes. RESULTS: Between 1988 and 2009, 1593 devices were implanted in patients in Western Australia, rising from 2 in 1988 to 245 in 2009; standardized population rates rose from 0.8 in 100000 in 1995 to 14.9 in 100000 in 2009. Mean age rose from 52.6 (SD 11.6) to 64.1 (11.4) years. Ventricular tachycardia (23%), cardiomyopathy (18%), and heart failure (16%) were the most frequent principal diagnoses. Ischemic heart disease was present in 49% of patients. Five-year cumulative survival was 0.74 (SE 0.01), and at 10 years, 0.53 (SE 0.03); median survival was 11.3 years. Readmission within a year, older age, heart failure, device complications, and chronic ischemic heart disease were associated with poorer survival. CONCLUSIONS: Implantable cardioverter-defibrillator use in adults at risk for sudden cardiac death has grown rapidly. Readmission within 12 months of discharge is associated with worse medium and long-term mortality. Survival for most patients younger than 65 years exceeds 10 years and 5 years for those aged ≥75 years.

Impact of the introduction of drug eluting stents on clinical outcomes in patients undergoing percutaneous and surgical coronary artery revascularisation procedures in Western Australia.

BACKGROUND: Increasing rates of percutaneous coronary intervention (PCI) and decreasing rates of coronary artery bypass graft (CABG) surgery followed the introduction of drug eluting stents in Western Australia in 2002. We assessed the impact of these changes on one-year outcomes for the total population of patients undergoing coronary artery revascularisation procedures (CARP) in Western Australia between 2000-2004. METHODS: Clinical and linked administrative data (inpatient admissions and death) were merged for all patients who had their first CARP with stent or CABG in Western Australia between 2000-2004. The clinical data were collected from all hospitals in Western Australia where CARP procedures are performed. We calculated the unadjusted (Kaplan-Meier) and adjusted (Cox) risks for one-year death (all-cause), death (all-cause) or admission for myocardial infarction (MI), target vessel revascularisation (TVR) and the composite outcome of death/MI/TVR (major adverse cardiac events, MACE). RESULTS: Over the study period, there were 14,118 index CARPs. The use of drug eluting stents increased from 0% to 95.8% of PCI procedures, and PCI procedures increased from 61.1% to 74.4% of all CARPS. There were no temporal changes in adjusted one-year mortality or death/MI. Overall, adjusted one-year MACE fell from 11.3% in 2000 to 8.5% in 2004 (p<0.0001) due to a significant reduction in TVR in the PCI group. CONCLUSION: The introduction of drug eluting stents and resulting changes in coronary revascularisation strategies were not associated with changes in the one-year risk of major clinical endpoints (death or death/MI), but were associated with a significant reduction in the risk of MACE, driven entirely by a reduction in TVR after PCI. This real world study supports the effectiveness of drug eluting stents in reducing repeat procedures in the total CARP population without increasing the risk of death or MI.

Voting with their feet--predictors of discharge against medical advice in Aboriginal and non-Aboriginal ischaemic heart disease inpatients in Western Australia: an analytic study using data linkage.

BACKGROUND: Discharge Against Medical Advice (DAMA) from hospital is associated with adverse outcomes and is considered an indicator of the responsiveness of hospitals to the needs of Aboriginal and Torres Strait Islander Australians, the indigenous people of Australia. We investigated demographic and clinical factors that predict DAMA in patients experiencing their first-ever inpatient admission for ischaemic heart disease (IHD). The study focuses particularly on the differences in the risk of DAMA in Aboriginal and non-Aboriginal patients while also investigating other factors in their own right. METHODS: A cross-sectional analytical study was undertaken using linked hospital and mortality data with complete coverage of Western Australia. Participants included all first-ever IHD inpatients (aged 25-79 years) admitted between 2005 and 2009, selected after a 15-year clearance period and who were discharged alive. The main outcome measure was DAMA as reflected in the hospital record.Multiple logistic regression was used to determine disparities in DAMA between Aboriginal and non-Aboriginal patients, adjusting for a range of demographic and clinical factors, including comorbidity based on 5-year hospitalization history. A series of additional models were run on subgroups of the cohort to refine the analysis. Ethics approval was granted by the WA Human Research and the WA Aboriginal Health Ethics Committees. RESULTS: Aboriginal patients comprised 4.3% of the cohort of 37,304 IHD patients and 23% of the 224 DAMAs. Emergency admission (OR=5.9, 95% CI 2.9-12.2), alcohol admission history (alcohol-related OR=2.9, 95% CI 2.0-4.2) and Aboriginality (OR 2.3, 95% CI 1.5-3.5) were the strongest predictors of DAMA in the multivariate model. Patients living in rural areas while attending non-metropolitan hospitals had a 50% higher risk of DAMA than those living and hospitalised in metropolitan areas. There was consistency in the ORs for Aboriginality in the different multivariate models using restricted sub-cohorts and different Aboriginal identifiers. Sex, IHD diagnosis type and co-morbidity scores imparted different risks in Aboriginal versus non-Aboriginal patients. CONCLUSIONS: Understanding the risks and reasons for DAMA is important for health system policy and proactive management of those at risk of DAMA. Improving care to prevent DAMA should target unplanned admissions, rural hospitals and young men, Aboriginal people and those with alcohol and mental health comorbidities.

Complex impact of remoteness on the incidence of myocardial infarction in Aboriginal and non-Aboriginal people in Western Australia.

OBJECTIVE: To determine the impact of remoteness on Aboriginal and non-Aboriginal myocardial infarction incidence rates in men and women of different ages. DESIGN: Descriptive study. SETTING: Western Australia. PARTICIPANTS: Incident cases of myocardial infarction in Western Australia from 2000-2004 identified from person-linked files of hospital and mortality records. Analysis was undertaken for Aboriginal and non-Aboriginal populations, separately and combined, by broad age group, sex and remoteness. MAIN OUTCOME MEASURE: Incidence of myocardial infarction. RESULTS: In the combined analysis, age-standardised incidence was significantly higher for men in very remote areas (rate ratio 1.31: 95% confidence interval (CI), 1.19-1.45) and in women in both regional (rate ratio 1.12: 95% CI, 1.01-1.20) and very remote (rate ratio 2.05: 95% CI, 1.75-2.41) areas. Aboriginal rates were substantially higher than non-Aboriginal rates in all substrata. Compared with metropolitan people, regional Aboriginal men and very remote non-Aboriginal men aged 25-54 years had significantly higher incidence rates. For the remaining rural strata, there was either no geographical disadvantage or inconclusive findings. CONCLUSIONS: Non-metropolitan disadvantage in myocardial infarction rates is confirmed in regional areas and women in very remote areas. This disadvantage is partly explained by the high rates in Aboriginal people. Non-metropolitan dwellers are not uniformly disadvantaged, reflecting the interplay of the many factors contributing to the complex relationship between myocardial infarction incidence and sex, age, Aboriginality and residence. Aboriginal Western Australians in all regions and young non-Aboriginal men living in very remote areas need to be targeted to reduce disparities in myocardial infarction.

Can we monitor heart attack in the troponin era? Evidence from a population-based cohort study.

BACKGROUND: Troponins (highly sensitive biomarkers of myocardial damage) increase counts of myocardial infarction (MI) in clinical practice, but their impact on trends in admission rates for MI in National statistics is uncertain. METHODS: Cases coded as MI or other cardiac diagnoses in the Hospital Morbidity Data Collection (MI-HMDC) in Western Australia in 1998 and 2003 were classified using revised criteria for MI developed by an International panel convened by the American Heart Association (AHA criteria) using information on symptoms, ECGs and cardiac biomarkers abstracted from samples of medical notes. Age-sex standardized rates of MI-HMDC were compared with rates of MI based on AHA criteria including troponins (MI-AHA) or traditional biomarkers only (MI-AHAck). RESULTS: Between 1998 and 2003, rates of MI-HMDC decreased by 3.5% whereas rates of MI-AHA increased by 17%, a difference largely due to increased false-negative cases in the HMDC associated with marked increased use of troponin tests in cardiac admissions generally, and progressively lower test thresholds. In contrast, rates of MI-AHAck declined by 18%. CONCLUSIONS: Increasing misclassification of MI-AHA by the HMDC may be due to reluctance by clinicians to diagnose MI based on relatively small increases in troponin levels. These influences are likely to continue. Monitoring MI using AHA criteria will require calibration of commercially available troponin tests and agreement on lower diagnostic thresholds for epidemiological studies. Declining rates of MI-AHA ck are consistent with long-standing trends in MI in Western Australia, suggesting that neither MI-HMDC nor MI-AHA reflect the true underlying population trends in MI.

Under-ascertainment of Aboriginality in records of cardiovascular disease in hospital morbidity and mortality data in Western Australia: a record linkage study.

BACKGROUND: Measuring the real burden of cardiovascular disease in Australian Aboriginals is complicated by under-identification of Aboriginality in administrative health data collections. Accurate data is essential to measure Australia's progress in its efforts to intervene to improve health outcomes of Australian Aboriginals. We estimated the under-ascertainment of Aboriginal status in linked morbidity and mortality databases in patients hospitalised with cardiovascular disease. METHODS: Persons with public hospital admissions for cardiovascular disease in Western Australia during 2000-2005 (and their 20-year admission history) or who subsequently died were identified from linkage data. The Aboriginal status flag in all records for a given individual was variously used to determine their ethnicity (index positive, and in all records both majority positive or ever positive) and stratified by region, age and gender. The index admission was the baseline comparator. RESULTS: Index cases comprised 62,692 individuals who shared a total of 778,714 hospital admissions over 20 years, of which 19,809 subsequently died. There were 3,060 (4.9%) persons identified as Aboriginal on index admission. An additional 83 (2.7%) Aboriginal cases were identified through death records, increasing to 3.7% when cases with a positive Aboriginal identifier in the majority (≥50%) of previous hospital admissions over twenty years were added and by 20.8% when those with a positive flag in any record over 20 years were incorporated. These results equated to underestimating Aboriginal status in unlinked index admission by 2.6%, 3.5% and 17.2%, respectively. Deaths classified as Aboriginal in official records would underestimate total Aboriginal deaths by 26.8% (95% Confidence Interval 24.1 to 29.6%). CONCLUSIONS: Combining Aboriginal determinations in morbidity and official death records increases ascertainment of unlinked cardiovascular morbidity in Western Australian Aboriginals. Under-identification of Aboriginal status is high in death records.

Incidence of and case fatality following acute myocardial infarction in Aboriginal and non-Aboriginal Western Australians (2000-2004): a linked data study.

BACKGROUND: Despite Coronary Heart Disease exacting a heavy toll among Aboriginal Australians, accurate estimates of its epidemiology are limited. This study compared the incidence of acute myocardial infarction (AMI) and 28-day case fatality (CF) among Aboriginal and non-Aboriginal Western Australians aged 25-74 years from 2000-2004. METHODS: Incident (AMI hospital admission-free for 15 years) AMI events and 28-day CF were estimated using person-based linked hospital and mortality data. Age-standardised incidence rates and case fatality percentages were calculated by Aboriginality and sex. RESULTS: Of 740 Aboriginal and 6933 non-Aboriginal incident events, 208 and 2352 died within 28 days, respectively. The Aboriginal age-specific incidence rates were 27 (males) and 35 (females) times higher than non-Aboriginal rates in the 25-29 year age group, decreasing to 2-3 at 70-74 years. The male:female age-standardised incidence rate ratio was 2.2 in Aboriginal people 25-54 years compared with 4.5 in non-Aboriginal people. Aboriginal age-standardised CF percentages were 1.4 (males) and 1.1 (females) times higher at age 25-54 years and 1.5 times higher at age 55-74 years. CONCLUSION: These data suggest higher CF and, more importantly, AMI incidence contribute to the excess ischaemic heart disease mortality in Aboriginal Western Australians. The poorer cardiovascular health in Aboriginal women, particularly in younger age groups, should be investigated.

Exploring the effects of transfers and readmissions on trends in population counts of hospital admissions for coronary heart disease: a Western Australian data linkage study.

OBJECTIVES: To develop a method for categorising coronary heart disease (CHD) subtype in linked data accounting for different CHD diagnoses across records, and to compare hospital admission numbers and ratios of unlinked versus linked data for each CHD subtype over time, and across age groups and sex. DESIGN: Cohort study. DATA SOURCE: Person-linked hospital administrative data covering all admissions for CHD in Western Australia from 1988 to 2013. MAIN OUTCOME: Ratios of (1) unlinked admission counts to contiguous admission (CA) counts (accounting for transfers), and (2) 28-day episode counts (accounting for transfers and readmissions) to CA counts stratified by CHD subtype, sex and age group. RESULTS: In all CHD subtypes, the ratios changed in a linear or quadratic fashion over time and the coefficients of the trend term differed across CHD subtypes. Furthermore, for many CHD subtypes the ratios also differed by age group and sex. For example, in women aged 35-54 years, the ratio of unlinked to CA counts for non-ST elevation myocardial infarction admissions in 2000 was 1.10, and this increased in a linear fashion to 1.30 in 2013, representing an annual increase of 0.0148. CONCLUSION: The use of unlinked counts in epidemiological estimates of CHD hospitalisations overestimates CHD counts. The CA and 28-day episode counts are more aligned with epidemiological studies of CHD. The degree of overestimation of counts using only unlinked counts varies in a complex manner with CHD subtype, time, sex and age group, and it is not possible to apply a simple correction factor to counts obtained from unlinked data.

Is the incidence of heart attack still decreasing in Australia? Developing reliable methods for monitoring trends in myocardial infarction and coronary heart disease (AUS-MOCHA): a study protocol.

INTRODUCTION: Accurate monitoring of acute coronary heart disease (CHD) is essential for understanding the effects of primary and secondary prevention and for planning of healthcare services. The ability to reliably monitor acute CHD has been affected by new diagnostic tests for myocardial infarction (MI) and changing clinical classifications and management of CHD. Our study will develop new and reliable methods for monitoring population trends in incidence, outcomes and health service usage for acute CHD and chest pain. METHODS AND ANALYSIS: The study cohort of all CHD will be identified from the Western Australian Data Linkage System using state-wide data sets for emergency department presentation, hospitalisations and mortality data for 2002-2014. This core linked data set will be supplemented with data from hospital medical record reviews, pathology data and hospital pharmacy dispensing databases. The consistency over time of the coding of the different subgroups of CHD/chest pain (ST-elevation MI, non-ST elevation MI, unstable angina, stable angina, other CHD, non-CHD chest pain) in linked data will be assessed using these data sources, and an algorithm developed detailing groups in which temporal trends can be reliably measured. This algorithm will be used for measurement of trends in incidence and outcomes of acute CHD, and to develop further methods for monitoring acute CHD using unlinked and linked data with varying availability of hospitalisation history. ETHICS AND DISSEMINATION: Ethics approval has been obtained from the Human Research Ethics Committees of the WA Department of Health (#2016/23) and The University of Western Australia (RA/4/1/7230). Findings will be disseminated via publication in peer-reviewed journals, and presentation at national and international conferences. There will also be a strong platform for dissemination of new monitoring methods via collaboration with the Australian Institute of Health and Welfare which will assist with promotion of these methods at state and national levels.

Secondary preventive medication use in a prevalent population-based cohort of acute coronary syndrome survivors.

AIM: Describe the dispensing patterns for guideline-recommended medications during 2008 in people with acute coronary syndrome (ACS) and how dispensing varies by gender and time since last ACS hospitalization. METHOD: A descriptive cohort spanning 20 years of people alive post-ACS in 2008. We extracted all ACS hospitalizations and deaths in Western Australia (1989-2008), and all person-linked Pharmaceutical Benefits Scheme claims nationally for 2008. Participants were 23 642 men and women (36.8%), alive and aged 65-89 years in mid-2008 who were hospitalized for ACS between 1989 and 2008. Main outcome was the proportion of the study cohort (in 2008) dispensed guideline-recommended cardiovascular medications in that year. Adjusted odds ratios estimating the association between type (and number) of guideline-recommended medications and time since last ACS hospitalization. RESULTS: Medications most commonly dispensed in 2008 were statins (79.6% of study cohort) and then angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers (ACEi/ARBs) (71.1%), aspirin or clopidogrel (59.4%), and ß-blockers (54.6%). Only 51.8% of the cohort was dispensed three or more of these drug types in 2008. Women with ACS were 18% less likely to be dispensed statins (adjusted odds ratio (OR)=0.82; 95% CI 0.76-0.88). Overall, for each incremental year since last ACS admission, there was an 8% increased odds (adjusted OR=1.08; 95% CI 1.07-1.08) of being dispensed fewer of the recommended drug regimen in 2008. CONCLUSION: Longer time since last ACS admission was associated with dispensing fewer medications types and combinations in 2008. Interventions are warranted to improve dispensing long term and any apparent gender inequality in the drug class filled.

Life expectancy after implantation of a first cardiac permanent pacemaker (1995-2008): A population-based study.

INTRODUCTION: Research suggests that survival among the recipients of a cardiac permanent pacemaker (PPM) matches the age- and sex-matched general population in the absence of cardiovascular disease. We used linked administrative data to examine life expectancy-based outcomes for adults requiring a cardiac PPM. METHODS: Population-level hospital admissions data were used to identify all recipients of an initial PPM during 1995-2008. Expected years of additional life remaining at the time of implantation were calculated for each patient from population life tables. Observed years were calculated using linked mortality data to end 2011. Cox regression was used to determine demographic and clinical predictors of survival. RESULTS: In 8757 patients age-adjusted risk of death to 5 years was associated with male sex, higher Charlson Comorbidity Index score (excluding cardiac disease), a history of heart failure, cardiomyopathy or atrial fibrillation and emergency admission. Coronary revascularisation surgery reduced long-term risk. The observed/expected ratio of additional years of life was 0.80 for men and 0.84 for women overall, varying from 0.92 for women without significant comorbidity to 0.40 for patients with the highest Charlson score and cardiomyopathy. The oldest patients (80-99 years) did relatively well, probably reflecting patient selection. Heart disease was the most frequent cause of death. CONCLUSIONS: Life expectancy among PPM recipients without significant comorbidity approached that of the general population. Greater non-cardiac comorbidity, heart failure, atrial fibrillation and, in particular, cardiomyopathy, contributed most to the loss of expected years of life in all age groups. The oldest patients and women did relatively well.

Initial hospitalisation for atrial fibrillation in Aboriginal and non-Aboriginal populations in Western Australia.

OBJECTIVE: The epidemiology of atrial fibrillation (AF) among Aboriginal Australians is poorly described. We compared risk factors, incidence rates and mortality outcomes for first-ever hospitalised AF among Aboriginal and non-Aboriginal Western Australians 20-84 years. METHODS: This retrospective cohort study used whole-of-state person-based linked hospital and deaths data. Incident hospital AF admissions (previous AF admission-free for 15 years) were identified and subsequent mortality determined. Disease-specific comorbidity histories were ascertained by 10-year look-back. Age-standardised incidence rates were estimated and the adjusted risk of 30-day and 1-year mortality calculated using regression methods. RESULTS: Aboriginal patients accounted for 923 (2.5%) of 37 097 incident AF admissions during 2000-2009. Aboriginal patients were younger (mean age 54.8 vs 69.3 years), had lower proportions of primary field AF diagnoses and higher comorbidities than non-Aboriginal patients. The Aboriginal and non-Aboriginal age-standardised incidence rates per 100,000 for men 20-54 years were 197 and 55 (ratio=3.6), for women 20-54 years were 122 and 19 (ratio=6.4), for men 55-84 years were 1151 and 888 (ratio=1.3), and for women 55-84 years were 1050 and 571 (ratio=1.8). While 30-day mortality was similar, crude 1-year mortality risks in Aboriginal and non-Aboriginal patients were 20.6% and 16.3% (adjusted HR=1.24) and 14.4% and 9.9% in 30-day survivors (adjusted HR=1.58). CONCLUSIONS: The incidence (particularly at young ages) and long-term mortality following hospitalised AF is significantly higher in Aboriginal people. Better control of the antecedent risk factors for AF, improved detection and management of AF itself and prevention of its complications are needed.

Improved methods for estimating incidence from linked hospital morbidity data.

BACKGROUND: Linked hospital morbidity data can be used to estimate the incidence of serious chronic disease. However, incidence rates calculated from first-time hospital admissions tend to be overestimated as a result of the erroneous inclusion of prevalent cases that have had previous hospital admissions prior to the study observation period. To address this problem, we have developed the backcasting method. METHOD: A retrograde survival model was implemented to calculate the level of over-ascertainment of incidence according to the number of years of linked data on which the estimates were based and corresponding correction factors were calculated. The method is illustrated using the example of linked hospital morbidity data on diabetes mellitus and then acute myocardial infarction, which was validated against the Perth MONICA database for cardiovascular disease. RESULTS: Corrected estimates of the incidence of diabetes and acute myocardial infarction were produced. The incidence of diabetes was shown to be lower than in North America in accordance with prevalence estimates, whereas the incidence of acute myocardial infarction was overestimated by approximately 10%. CONCLUSION: A new method is presented for estimating incidence trends in disease from linked hospital morbidity data. The advantages of this method are its ease of use with routinely collected data and the relatively low cost of applying it in comparison with community surveys or maintaining formal disease registers. The method has other applications using linked data, such as the study of trends in first-time health care procedures and pharmaceutical prescriptions.

Trends in the incidence and prevalence of cardiac pacemaker insertions in an ageing population.

OBJECTIVES: To determine contemporary population estimates of the prevalence of cardiac permanent pacemaker (PPM) insertions. METHODS: A population-based observational study using linked hospital morbidity and death registry data from Western Australia (WA) to identify all incident cases of PPM insertion for adults aged 18 years or older. Prevalence rates were calculated by age and sex for the years 1995-2009 for the WA population. RESULTS: There were 9782 PPMs inserted during 1995-2009. Prevalence rose across the study period, exceeding 1 in 50 among people aged 75 or older from 2005. This was underpinned by incidence rates which rose with age, being highest in those 85 years or older; over 500/100 000 for men throughout, and over 200/100 000 for women. Rates for patients over 75 were more than double the rates for those aged 65-74 years. Women were around 40% of cases overall. The use of dual-chamber and triple-chamber pacing increased across the study period. A cardiac resynchronisation defibrillator was implanted for 58% of patients treated with cardiac resynchronisation therapy. CONCLUSIONS: Rates of insertion and prevalence of PPM continue to rise with the ageing population in WA. As equilibrium has probably not been reached, the demand for pacing services in similarly well-developed economies is likely to continue to grow.

Prevalence of stroke and coexistent conditions: disparities between indigenous and nonindigenous Western Australians.

BACKGROUND: Worldwide, the prevalence of stroke is poorly described in indigenous populations, despite high stroke burden. This paper reports the average point prevalence of hospitalized stroke and coexistent conditions (2007-2011) in indigenous and nonindigenous people in Western Australia, the largest and most sparsely populated Australian jurisdiction. METHODS: Using state-wide linked hospital and mortality data, indigenous and nonindigenous prevalent stroke cases (aged 25-84 years) were identified after reviewing stroke admissions over a fixed 20-year look-back period. Prevalent cases were those alive at midyear of each study year. The 2007-2011 period prevalence was a weighted average of annual prevalence. Histories of 11 comorbidities were identified using the 20-year look-back period. RESULTS: Indigenous cases comprised 5% of the average 13 591 annual prevalent cases. Indigenous patients were more likely to be younger, female, and have unknown stroke type. Indigenous prevalence was higher at every age. The age-standardized prevalence in indigenous men (33·7 per 1000; 95% confidence interval 31·9-35·4) was 3.7 times greater than in nonindigenous men (9·1 per 1000; 95% confidence interval 9·0-9·2). The corresponding estimates for women were 27·1 per 1000 (25·7-28·4) and 6·1 per 1000 (6·0-6·2) (ratio = 4·4). The percentage with selected comorbid conditions was substantially higher for indigenous patients. CONCLUSIONS: The high stroke prevalence in indigenous Western Australians, coupled with clinical complexity from comorbid conditions, requires access to culturally appropriate medical, rehabilitation, and logistical support. Intensified primary and secondary prevention is needed to reduce the impact of stroke on indigenous people.