CSIRO PUBLISHING
Australian Health Review http://dx.doi.org/10.1071/AH14226
Sudden cardiac death rates in an Australian population: a data linkage study Jia-Li Feng1,5 MB, MM, PhD candidate Siobhan Hickling1 BSc, Grad Dip Diet, MPH, PhD, Assistant Professor Lee Nedkoff1 BSc(Physiotherapy), MPH, Research Associate Matthew Knuiman1 BSc(Hons), PhD, Winthrop Professor Christopher Semsarian2,3,4 MBBS, PhD, Professor Jodie Ingles3,4 BBiomedSc, GradDipGenCouns, PhD, Conjoint Senior Lecturer Tom G. Briffa1 BPhysEd, MPhysEd, PhD, Research Associate Professor 1
School of Population Health, Faculty of Medicine, Dentistry and Health Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. Email: [email protected]; [email protected]; [email protected]; [email protected] 2 Department of Cardiology, Royal Prince Alfred Hospital, 50 Missenden Road, Camperdown, NSW 2050, Australia. 3 Agnes Ginges Centre for Molecular Cardiology, Centenary Institute, , Building 93, Newtown, NSW 2042, Australia. Email: [email protected], [email protected] 4 Sydney Medical School, Edward Ford Building A27, The University of Sydney, NSW 2006, Australia. 5 Corresponding author. Email: [email protected]
Abstract Objective. The aim of the present study was to develop criteria to identify sudden cardiac death (SCD) and estimate population rates of SCD using administrative mortality and hospital morbidity records in Western Australia. Methods. Four criteria were developed using place, death within 24 h, principal and secondary diagnoses, underlying and associated cause of death, and/or occurrence of a post mortem to identify SCD. Average crude, age-standardised and age-specific rates of SCD were estimated using population person-linked administrative data. Results. In all, 9567 probable SCDs were identified between 1997 and 2010, with one-third aged 35 years having no prior admission for cardiovascular disease. SCD was more frequent in men (62.1%). The estimated average annual crude SCD rate for the period was 34.6 per 100 000 person-years with an average annual age-standardised rate of 37.8 per 100 000 person-years. Age-specific standardised rates were 1.1 per 100 000 person-years and 70.7 per 100 000 person-years in people aged 1–34 and 35 years, respectively. Ischaemic heart disease (IHD) was recorded as the underlying cause of death in approximately 80% of patients aged 35 years, followed by valvular heart disease and heart failure. IHD was the most common cause of death in those aged 1–34 years, followed by unspecified cardiomyopathy and dysrhythmias. Conclusions. Administrative morbidity and mortality data can be used to estimate rates of SCD and therefore provide a suitable methodology for monitoring SCD over time. The findings highlight the magnitude of SCD and its potential for public health prevention. What is known about the topic? There is considerable variability in rates of SCD worldwide. Different data sources and varied methods of case ascertainment likely contribute to this variation. What does this paper add? The rate of SCD in Australia is low compared with international estimates from USA, Ireland, Netherlands and China. Two in every three cases of SCD aged 35 years had a hospitalisation history of cardiovascular disease, highlighting the opportunity for prevention. What are the implications for practitioners? High-quality person-linked administrative hospital morbidity and registered mortality data can be used to estimate rates of SCD in the population. Understanding the magnitude and distribution of SCD is imperative for developing effective public health policy and prevention measures. Received 23 November 2014, accepted 11 March 2015, published online 18 May 2015
Journal compilation AHHA 2015
www.publish.csiro.au/journals/ahr
B
Australian Health Review
Introduction Cardiovascular disease (CVD) is a leading cause of mortality worldwide, accounting for more than 17 million deaths annually.1 Up to 50% of all such deaths are sudden,2 highlighting sudden cardiac death (SCD) as a public health concern. There is considerable variation in rates of SCD, which range from 60 to >150 per 100 000 person-years in the US3,4 and between 40 and 100 per 100 000 person-years in Europe and Asia.5–8 Such differences are likely due to varied data sources and different methods of case ascertainment. New strategies for SCD case ascertainment, such as the use of routinely collected administrative morbidity and mortality data, offer an opportunity to derive estimates of SCD rates over time and thereby advance our knowledge and provide a platform for its prevention. Few population studies of SCD are Australian. An indirect measure of SCD in Western Australia (WA) estimated the out-ofhospital cardiac arrest rate to be 60.2 per 100 000 person-years.9 An earlier small Australian study estimated the out-of-hospital SCD rate to be 40 per 100 000 person-years in those aged 25–94 years.10 In addition, two studies from Australia and New Zealand report low rates of SCD in those aged 1–35 years (1.1 per 100 000 person-years)11 and 0–40 years (2.0 per 100 000 personyears),12 respectively. The contrasting age-specific difference in rates of SCD is likely explained by the disparities in underlying mechanisms that occur with age, methodologies for case ascertainment and definitions of SCD.13 Improving our knowledge of SCD is contingent upon having a consistent, reliable and measurable definition. The widely accepted definition of SCD is unexpected natural death that occurs within 1 h of the onset of symptoms if death is witnessed, and within 24 h of being seen alive and well when unwitnessed.14 However, this definition is difficult to apply because of problems in determining the precise timing from symptom onset to cardiac collapse and the fact that many SCD cases go unwitnessed,5,15 despite many of them occurring at home.7 As argued by others,14 the definition of SCD should be less specific and sufficiently flexible for an epidemiological study that sheds light on the general population rather than individual cases. Further, there is no national registry for SCD in Australia, and thus the population impact of this life-ending event is poorly understood. Despite the availability of a specific code for SCD in the International Classification of Diseases (ICD), SCD is rarely coded as the cause of death (COD). This is likely due to coding guidelines stating the SCD code may only be assigned if resuscitation is administered regardless of patient outcome. The objectives of the present study were to develop criteria for the identification of probable SCD cases using population-wide person-based administrative morbidity and mortality data and to quantify the magnitude of SCD in a representative Australian state. Methods Population In 2010, the population of WA was 2.3 million, 75% of whom resided in the capital city, Perth.16 Net overseas and interstate migration rates are low and estimated at 1.3% and 0.1%, respectively.16 WA has comparable key sociodemographic and health economic indicators with other Australian states, including age,
J.-L. Feng et al.
sex, Indigenous status, rural and remote population, out-of-state migration, available hospital beds, health expenditure and Medicare benefits paid.17 Data sources In Australia, the patient’s hospital chart is the primary source of information for the coding of in-patient morbidity. ICD codes for episodes of care and comorbidities are recorded using information from the patient discharge summary and the clinical notes. Information about a death is recorded on a death certificate, and coded by the Australian Bureau of Statistics (ABS).18 Death certification on a natural unexpected death is completed in one of two ways: (1) the police, funeral director and/or the medical practitioner provide supporting evidence and a determination as to the COD; or (2) if none of these groups can certify the COD, then the case is referred to a coroner for a determination where police investigation, autopsy and toxicology analysis are involved.18 Where the coroner is unable to reach a decision on a case, a recommendation is made to assign a code for an undetermined death, as regulated by the ABS.19 Data linkage system Administrative data for all hospital morbidity records and deaths in WA are contained in the Hospital Morbidity Data Collection (HMDC) and Mortality Register, respectively, both of which are regularly audited for quality.20 These records are linked at an individual level through the WA Data Linkage System by probabilistic matching, with an accuracy of >99%.20 The morbidity dataset covers all public and private hospital admissions in WA. The mortality dataset covers multiple COD, including underlying and associated causes (e.g. direct, antecedent and contributory causes) and occurrence of a post mortem. Contributory causes were excluded from the present study because they are pre-existing conditions and do not directly influence the death.18 Multiple COD data in WA became available for research from 1997 onwards. The linked dataset for the present study contains all hospital admissions and death records for CVD from 1987 to 2010, permitting a 10-year look-back period for CVD hospitalisation history. Criteria for SCD cases Four criteria were developed to identify probable SCD cases (Table 1). Each criterion used a combination of two or three components including place, death within 24 h, diagnoses, underlying cause and/or additional information (associated COD and occurrence of a post mortem). We estimated death within 24 h using admission and death dates. No priority was applied to any of the components in each criterion. Some cases were identified by more than one criterion but only counted once. The prevailing ICD version and relevant modifications (ICD-9 from 1 July 1979 and ICD-10 from 1 July 1999) were used to identify cases. The term ‘SCD-related disease’ was created to incorporate several conditions from the literature known to be associated with SCD and included myocardial infarction (MI), other ischaemic heart disease (IHD), cardiomyopathy, conduction disorder, ventricular fibrillation (VF), ventricular tachycardia (VT), cardiac arrest, other dysrhythmias, heart failure, myocarditis, endocarditis, pericarditis, valvular heart disease, pulmonary heart disease, rheumatic heart disease and congenital heart disease3,15
Sudden cardiac death rates data linkage study
Australian Health Review
C
Table 1. Criteria for probable sudden cardiac death identification COD, cause of death; SCD, sudden cardiac death; VF, ventricular fibrillation; VT, ventricular tachycardia; MI, myocardial infarction Place, time, diagnosis Criterion 1
Criterion 2
Criterion 3
Criterion 4
Died out of hospital OR died in hospital 24 h of any-cause admission Died in hospital 24 h of admission for VF, VT or cardiac arrest recorded in any diagnostic field Died out of hospital OR died in hospital 24 h of any-cause admission Died out of hospital OR died in hospital following an admission for MI as principal diagnosis within past 28 days
Underlying cause (from death record) AND
Underlying COD was an SCD-related diseaseA
AND
Underlying COD was an SCD-related diseaseA
AND
Underlying COD was an SCD-related diseaseA
AND
Underlying COD was an SCD-related diseaseA
Additional information (from death record) AND
Associated CODB was VF, VT or cardiac arrest
AND
Indications of whether post-mortem was conducted
‘SCD-related disease’ included ischaemic heart disease, cardiomyopathy, dysrhythmias, heart failure, myocarditis, endocarditis, pericarditis, valvular heart disease, pulmonary heart disease, rheumatic heart disease, and congenital heart disease. B ‘Associated COD’ included direct and antecedent cause(s) as determined from the death record.
A
(see Table S1 available as Supplementary Material for this paper). Inclusion of all IHD codes is based on previous validation studies in Australia21 and international recommendations for identifying coronary heart disease deaths from administrative data.22 We excluded cases aged
Australian Health Review http://dx.doi.org/10.1071/AH14226
Sudden cardiac death rates in an Australian population: a data linkage study Jia-Li Feng1,5 MB, MM, PhD candidate Siobhan Hickling1 BSc, Grad Dip Diet, MPH, PhD, Assistant Professor Lee Nedkoff1 BSc(Physiotherapy), MPH, Research Associate Matthew Knuiman1 BSc(Hons), PhD, Winthrop Professor Christopher Semsarian2,3,4 MBBS, PhD, Professor Jodie Ingles3,4 BBiomedSc, GradDipGenCouns, PhD, Conjoint Senior Lecturer Tom G. Briffa1 BPhysEd, MPhysEd, PhD, Research Associate Professor 1
School of Population Health, Faculty of Medicine, Dentistry and Health Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. Email: [email protected]; [email protected]; [email protected]; [email protected] 2 Department of Cardiology, Royal Prince Alfred Hospital, 50 Missenden Road, Camperdown, NSW 2050, Australia. 3 Agnes Ginges Centre for Molecular Cardiology, Centenary Institute, , Building 93, Newtown, NSW 2042, Australia. Email: [email protected], [email protected] 4 Sydney Medical School, Edward Ford Building A27, The University of Sydney, NSW 2006, Australia. 5 Corresponding author. Email: [email protected]
Abstract Objective. The aim of the present study was to develop criteria to identify sudden cardiac death (SCD) and estimate population rates of SCD using administrative mortality and hospital morbidity records in Western Australia. Methods. Four criteria were developed using place, death within 24 h, principal and secondary diagnoses, underlying and associated cause of death, and/or occurrence of a post mortem to identify SCD. Average crude, age-standardised and age-specific rates of SCD were estimated using population person-linked administrative data. Results. In all, 9567 probable SCDs were identified between 1997 and 2010, with one-third aged 35 years having no prior admission for cardiovascular disease. SCD was more frequent in men (62.1%). The estimated average annual crude SCD rate for the period was 34.6 per 100 000 person-years with an average annual age-standardised rate of 37.8 per 100 000 person-years. Age-specific standardised rates were 1.1 per 100 000 person-years and 70.7 per 100 000 person-years in people aged 1–34 and 35 years, respectively. Ischaemic heart disease (IHD) was recorded as the underlying cause of death in approximately 80% of patients aged 35 years, followed by valvular heart disease and heart failure. IHD was the most common cause of death in those aged 1–34 years, followed by unspecified cardiomyopathy and dysrhythmias. Conclusions. Administrative morbidity and mortality data can be used to estimate rates of SCD and therefore provide a suitable methodology for monitoring SCD over time. The findings highlight the magnitude of SCD and its potential for public health prevention. What is known about the topic? There is considerable variability in rates of SCD worldwide. Different data sources and varied methods of case ascertainment likely contribute to this variation. What does this paper add? The rate of SCD in Australia is low compared with international estimates from USA, Ireland, Netherlands and China. Two in every three cases of SCD aged 35 years had a hospitalisation history of cardiovascular disease, highlighting the opportunity for prevention. What are the implications for practitioners? High-quality person-linked administrative hospital morbidity and registered mortality data can be used to estimate rates of SCD in the population. Understanding the magnitude and distribution of SCD is imperative for developing effective public health policy and prevention measures. Received 23 November 2014, accepted 11 March 2015, published online 18 May 2015
Journal compilation AHHA 2015
www.publish.csiro.au/journals/ahr
B
Australian Health Review
Introduction Cardiovascular disease (CVD) is a leading cause of mortality worldwide, accounting for more than 17 million deaths annually.1 Up to 50% of all such deaths are sudden,2 highlighting sudden cardiac death (SCD) as a public health concern. There is considerable variation in rates of SCD, which range from 60 to >150 per 100 000 person-years in the US3,4 and between 40 and 100 per 100 000 person-years in Europe and Asia.5–8 Such differences are likely due to varied data sources and different methods of case ascertainment. New strategies for SCD case ascertainment, such as the use of routinely collected administrative morbidity and mortality data, offer an opportunity to derive estimates of SCD rates over time and thereby advance our knowledge and provide a platform for its prevention. Few population studies of SCD are Australian. An indirect measure of SCD in Western Australia (WA) estimated the out-ofhospital cardiac arrest rate to be 60.2 per 100 000 person-years.9 An earlier small Australian study estimated the out-of-hospital SCD rate to be 40 per 100 000 person-years in those aged 25–94 years.10 In addition, two studies from Australia and New Zealand report low rates of SCD in those aged 1–35 years (1.1 per 100 000 person-years)11 and 0–40 years (2.0 per 100 000 personyears),12 respectively. The contrasting age-specific difference in rates of SCD is likely explained by the disparities in underlying mechanisms that occur with age, methodologies for case ascertainment and definitions of SCD.13 Improving our knowledge of SCD is contingent upon having a consistent, reliable and measurable definition. The widely accepted definition of SCD is unexpected natural death that occurs within 1 h of the onset of symptoms if death is witnessed, and within 24 h of being seen alive and well when unwitnessed.14 However, this definition is difficult to apply because of problems in determining the precise timing from symptom onset to cardiac collapse and the fact that many SCD cases go unwitnessed,5,15 despite many of them occurring at home.7 As argued by others,14 the definition of SCD should be less specific and sufficiently flexible for an epidemiological study that sheds light on the general population rather than individual cases. Further, there is no national registry for SCD in Australia, and thus the population impact of this life-ending event is poorly understood. Despite the availability of a specific code for SCD in the International Classification of Diseases (ICD), SCD is rarely coded as the cause of death (COD). This is likely due to coding guidelines stating the SCD code may only be assigned if resuscitation is administered regardless of patient outcome. The objectives of the present study were to develop criteria for the identification of probable SCD cases using population-wide person-based administrative morbidity and mortality data and to quantify the magnitude of SCD in a representative Australian state. Methods Population In 2010, the population of WA was 2.3 million, 75% of whom resided in the capital city, Perth.16 Net overseas and interstate migration rates are low and estimated at 1.3% and 0.1%, respectively.16 WA has comparable key sociodemographic and health economic indicators with other Australian states, including age,
J.-L. Feng et al.
sex, Indigenous status, rural and remote population, out-of-state migration, available hospital beds, health expenditure and Medicare benefits paid.17 Data sources In Australia, the patient’s hospital chart is the primary source of information for the coding of in-patient morbidity. ICD codes for episodes of care and comorbidities are recorded using information from the patient discharge summary and the clinical notes. Information about a death is recorded on a death certificate, and coded by the Australian Bureau of Statistics (ABS).18 Death certification on a natural unexpected death is completed in one of two ways: (1) the police, funeral director and/or the medical practitioner provide supporting evidence and a determination as to the COD; or (2) if none of these groups can certify the COD, then the case is referred to a coroner for a determination where police investigation, autopsy and toxicology analysis are involved.18 Where the coroner is unable to reach a decision on a case, a recommendation is made to assign a code for an undetermined death, as regulated by the ABS.19 Data linkage system Administrative data for all hospital morbidity records and deaths in WA are contained in the Hospital Morbidity Data Collection (HMDC) and Mortality Register, respectively, both of which are regularly audited for quality.20 These records are linked at an individual level through the WA Data Linkage System by probabilistic matching, with an accuracy of >99%.20 The morbidity dataset covers all public and private hospital admissions in WA. The mortality dataset covers multiple COD, including underlying and associated causes (e.g. direct, antecedent and contributory causes) and occurrence of a post mortem. Contributory causes were excluded from the present study because they are pre-existing conditions and do not directly influence the death.18 Multiple COD data in WA became available for research from 1997 onwards. The linked dataset for the present study contains all hospital admissions and death records for CVD from 1987 to 2010, permitting a 10-year look-back period for CVD hospitalisation history. Criteria for SCD cases Four criteria were developed to identify probable SCD cases (Table 1). Each criterion used a combination of two or three components including place, death within 24 h, diagnoses, underlying cause and/or additional information (associated COD and occurrence of a post mortem). We estimated death within 24 h using admission and death dates. No priority was applied to any of the components in each criterion. Some cases were identified by more than one criterion but only counted once. The prevailing ICD version and relevant modifications (ICD-9 from 1 July 1979 and ICD-10 from 1 July 1999) were used to identify cases. The term ‘SCD-related disease’ was created to incorporate several conditions from the literature known to be associated with SCD and included myocardial infarction (MI), other ischaemic heart disease (IHD), cardiomyopathy, conduction disorder, ventricular fibrillation (VF), ventricular tachycardia (VT), cardiac arrest, other dysrhythmias, heart failure, myocarditis, endocarditis, pericarditis, valvular heart disease, pulmonary heart disease, rheumatic heart disease and congenital heart disease3,15
Sudden cardiac death rates data linkage study
Australian Health Review
C
Table 1. Criteria for probable sudden cardiac death identification COD, cause of death; SCD, sudden cardiac death; VF, ventricular fibrillation; VT, ventricular tachycardia; MI, myocardial infarction Place, time, diagnosis Criterion 1
Criterion 2
Criterion 3
Criterion 4
Died out of hospital OR died in hospital 24 h of any-cause admission Died in hospital 24 h of admission for VF, VT or cardiac arrest recorded in any diagnostic field Died out of hospital OR died in hospital 24 h of any-cause admission Died out of hospital OR died in hospital following an admission for MI as principal diagnosis within past 28 days
Underlying cause (from death record) AND
Underlying COD was an SCD-related diseaseA
AND
Underlying COD was an SCD-related diseaseA
AND
Underlying COD was an SCD-related diseaseA
AND
Underlying COD was an SCD-related diseaseA
Additional information (from death record) AND
Associated CODB was VF, VT or cardiac arrest
AND
Indications of whether post-mortem was conducted
‘SCD-related disease’ included ischaemic heart disease, cardiomyopathy, dysrhythmias, heart failure, myocarditis, endocarditis, pericarditis, valvular heart disease, pulmonary heart disease, rheumatic heart disease, and congenital heart disease. B ‘Associated COD’ included direct and antecedent cause(s) as determined from the death record.
A
(see Table S1 available as Supplementary Material for this paper). Inclusion of all IHD codes is based on previous validation studies in Australia21 and international recommendations for identifying coronary heart disease deaths from administrative data.22 We excluded cases aged
