Concept: Acute Myocardial Infarction (AMI) / Myocardial Infarction (MI) - Definition, Rates and Post-AMI Management

Introduction

This concept contains a brief conceptual definition of AMI and a detailed operational definition of how MCHP has defined AMI using administrative data. The concept also provides a list of MCHP research that has investigated AMI over time. Each research project listed provides a brief description of how AMI was investigated in the research and provides a link to the findings published in that specific research. The concept includes research that investigates overall AMI rates, as well as post-AMI management with medications, including beta-blockers and cholesterol lowering drug treatment.

Definition of Acute Myocardial Infarction (AMI) / Myocardial Infarction (MI)

Also known as a heart attack, a myocardial infarction occurs when the heart muscle (the myocardium) experiences sudden (acute) deprivation of circulating blood. The interruption of blood is usually caused by narrowing of the coronary arteries leading to a blood clot. The clogging frequently is initiated by cholesterol piling up on the inner wall of the blood vessels that distribute blood to the heart muscle (Martens et al., 2003).

NOTE: The terms acute myocardial infarction (AMI) and myocardial infarction (MI) are synonymous in MCHP research and are used interchangeably in this concept.

Defining Acute Myocardial Infarction (AMI) / Myocardial Infarction (MI) in Administrative Data

Different data sets have been used to define AMI in the administrative data in the MCHP Data Repository.


• The most common method of defining AMI in MCHP research is using ICD-9-CM code 410 or ICD-10-CA code I21 in the most responsible diagnosis field of the hospital abstracts data. In some cases all diagnoses fields are reviewed to identify the occurrence of AMI.
  
• In Fransoo et al. (2009), (2011), (2013), (2019) and Chartier et al. (2012), (2015) they included patients with AMI listed as the primary cause of death (ICD-10 code I21) in the Vital Statistics Mortality Registry data.

Additional ICD codes have been used to identify AMI/MI in some research. In Katz et al. (2010) and Katz et al. (2014), the definition of myocardial infarction also included ICD-10-CA code I22 (subsequent myocardial infarction).

Other considerations have been factored into the research-specific definitions of AMI/MI. For example:


• in Fransoo et al. (2009) and Katz et al. (2014), the definition was restricted to newly diagnosed patients aged 20+ when looking at post-myocardial treatment/management with medications.
  
• in Fransoo et al. (2009) and Martens et al. (2010) , the definition for AMI rates was restricted to residents age 40 or older.
  
• in Martens et al. (2010), and Fransoo et al. (2011), (2013), (2019) the definition for inpatient AMI hospitalization also required a length of stay of three days or more (unless the patient died in hospital), and they tracked transfers between hospitals to ensure all "true" AMI cases staying at least three days in hospital(s) were counted.
  
• in Chartier et al. (2015) the hospital AMI definition was restricted to most responsible diagnosis code with a length of stay of three or more days and was also restricted to Manitobans 40 years of age and older within a five year fiscal period.

AMI Rates Published in MCHP Research

The following list of research provides links to AMI rates published in different MCHP research:


• In Brownell et al. (2003), they provide relative rates of AMI hospitalization for the "least healthy" compared to the "most healthy" patients for both Winnipeg and non-Winnipeg populations. ("Health is based on the premature mortality rate for a region - by Winnipeg Neighbourhood Cluster or by RHA in non-Winnipeg areas). See the section titled AMI hospitalizations for more information on these relative rates.
  
  
• In Martens et al. (2003), they compare AMI treatment prevalence over two time periods (1991/92-1995/96 and 1996/97-2001/01) by RHA and RHA District. See section 5.4 Acute Myocardial Infarction (AMI) Treatment Prevalence for more information.
  
  
• In Fransoo et al. (2005), they compare AMI incidence rates for males and females over the time period 1998/99-2002/03 by RHA, RHA District, income quintile and age. See section 3.9 Acute Myocardial Infarction (AMI) Incidence rates (Hospitalization or Death) for more information.
  
  
• In Fransoo et al. (2009), they compare AMI rates over two time periods (1996/97-2000/01 and 2001/02-2005/06) by RHA, RHA Districts, and Winnipeg Neighbourhood Clusters (NC). See section 4.7 Acute Myocardial Infarction (Heart Attack) Rates for more information.
  
  
• In Martens et al. (2010), they compare AMI incidence rates of the Metis to all other Manitobans (2002/03-2006/07) by RHA and Winnipeg Aggregate Area, and look at incidence rates by Metis Region. See section 5.9 Acute Myocardial Infarction (AMI) Incidence Rates for more information.
  
  
• In Fransoo et al. (2011), they investigate AMI and obesity and report AMI relative risk and incidence rates by BMI (Body Mass Index) Group for males and females. See the section titled Acute Myocardial Infarction (AMI) for more information.
  
  
• In Chartier et al. (2012), they compare AMI rate ratios using a Francophone cohort and Other Manitoban cohort over a nine-year period from 1999/2000 to 2007/2008. See section 5.3 Acute Myocardial Infarction (AMI) for more information.
  
  
• In Fransoo et al. (2013), they compare AMI rates over two time periods (2002-2006 and 2007-2011) by RHA - for both current (5) and former (11) RHAs, RHA Districts, and Winnipeg Neighbourhood Clusters (NC). See section 4.11 Acute Myocardial Infarction (AMI) Rates for more information.
  
  
• In Chartier et al. (2015), they investigated the prevalence and relative risk of AMI as a comorbidity to end stage kidney disease (ESKD) and chronic kidney disease (CKD). For more information on prevalence and relative risk, see:
  
  • Table 4.1 Physical Health of Adults in End Stage Kidney Disease; and
    
  • Table 4.5 Physical Health of Adults in Chronic Kidney Disease.
  
  
• In Fransoo et al. (2019), they compare AMI rates over two time periods (2007-2011 and 2012-2016) by RHA. See section 4.13 Acute Myocardial Infarction (AMI) Rates for more information.

Post Myocardial Infarction (MI) Management with Medications

After initial treatment, clinical practice guidelines recommend both post-MI medication and lifestyle changes to prevent recurrence of a heart attack. This includes the use of beta-blockers that have been shown to lower the risk of subsequent MIs. The guidelines also recommend the prescription of cholesterol-lowering drugs for all patients after an MI regardless of cholesterol levels (Katz et al. (2014).

The following sections describe two indicators that measure MI management with each of these different medications, and provides access to research findings that report the measurement of these indicators.

1. Post MI Management with Beta-Blockers

Two indicators were developed to measure post MI management with beta-blockers. The first indicator measures the percentage of newly diagnosed MI patients who filled at least one beta-blocker prescription within four months of the hospital discharge at the time of the MI (initiation of use). The second indicator measures the percentage of patients who had a prescription filled for 80% of the days between hospital separation (of the MI diagnosis) and end of the study period (persistence of use).

Beta-blockers are defined by ATC codes C07AA and C07AB.

Exclusions: Patients diagnosed within the past three years with a diagnosis of asthma, COPD, or peripheral vascular disease are excluded, since these conditions are contra-indications for the use of these drugs. In addition, in some research (Martens et al. (2010) and Katz et al. (2014)), for both indicators, patients diagnosed within the past three years with a diagnosis of AMI (ICD-9-CM = 410 or ICD-10-CA = I21 or I22) were also excluded.

The following list of research provides links to the findings relevant to post-MI management with beta-blockers:


• In Katz et al. (2004), they compare the prevalence rates of beta-blocker prescribing for four different types of family physicians (FP) (Winnipeg FPs, Brandon FPs, Non-urban FPs and Manitoba FPs). See section 3.3.7 Post-Myocardial Infarction Care: Beta-Blocker Prescribing for more information.
  
  
• In Fransoo et al. (2005), they compare the rates of beta-blocker prescribing for males and females over a five year period (1999/2000 - 2003/04) by RHA, RHA District, income quintile and by age and sex. See section 11.4 Post-Acute Myocardial Infarction Care: Beta-Blocker Prescribing for more information.
  
  
• In Fransoo et al. (2009), they compare the rates of beta-blocker prescribing for two different time periods (1996/97-2000/01 with 2001/02-2005/06) by RHA, RHA District and Winnipeg Neighbourhood Clusters. See section 13.4 Post-AMI Care: Beta-Blocker Prescribing for more information.
  
  
• In Metge et al. (2009), they compare the rates of beta-blocker prescribing for two different time periods (2000/01-2002/03 with 2003/04-2005/06) by RHA and Winnipeg Neighbourhood Clusters. See section Figure 6.11 Percentage of Acute Myocardial Infarction (AMI) Patients Who Filled a Prescription for a Beta-Blocker Four Months After Their First AMI, by RHA for more information.
  
  
• In Martens et al. (2010), they compare the rates of beta-blocker prescribing for the Metis to all other Manitobans by RHA and Winnipeg Community area, and look at rates by Metis Region. See section 14.4 Post-AMI Care: Beta-Blockers for more information.
  
  
• In Martens et al. (2010), they compare the rates of beta-blocker prescribing over time (1996/97 to 2007/08) by income quintile. See the section titled Post-Acute Myocardial Infarction (AMI) Care: Beta-Blocker Prescribing for more information.
  
  
• In Katz et al. (2010), they compare the prevalence rates of these two indicators for four different groups of patients related to the implementation of Physician Integrated Network (PIN) clinics. See the section titled Post-Myocardial Infarction (MI) Care: Treatment with Beta-Blockers for more information.
  
  
• In Chartier et al. (2012), they compare the rate ratios of beta-blocker prescribing using a Francophone Cohort and Other Manitoban Cohort by RHA. See section 14.4 Post-AMI Care: Beta Blocker for more information.
  
  
• In Fransoo et al. (2013), they compare the rates of beta-blocker prescribing for two time periods (2002/03- 2006/07 with 2007/08-2011/12) by RHA - for both current (5) and former (11) RHAs, RHA Districts and Winnipeg Neighbourhood Cluster. See section 11.4 Post-AMI Care: Beta-Blocker Prescribing for more information.
  
  
• In Katz et al. (2014), they compare the rates of these two indicators related to the implementation of Physician Integrated Network (PIN) clinics. See the section titled Post Myocardial Infarction Management: Initiation and Persistence of Beta-Blocker Drug Treatment for more information.
  
  
• In Fransoo et al. (2019), they compare the rates of beta-blocker prescribing for two time periods (2007/08-2011/12 with 2012/13-2016/17) by RHA. See section 6.4 Post-AMI Care: Beta-Blocker Dispensations for more information.

2. Post MI Management with Cholesterol Lowering Drug Treatment

Two indicators were developed to measure post MI management with cholesterol lowering drug treatment. The first indicator measures the percentage of newly diagnosed MI patients who filled at least one cholesterol lowering prescription within four months of the hospital discharge at the time of the MI (initiation of use). The second indicator measures the percentage of patients who had a prescription filled for 80% of the days between hospital separation (of the MI diagnosis) and end of the study period (persistence of use).

Cholesterol lowering drugs, such as HMG CoA reductase inhibitors (statins), fibrates, bile acid sequestrates (resins), and nicotinic acid derived (niacin) are defined by ATC codes C10.

Exclusions: Patients with a prescription for cholesterol lowering drugs that occur up to one year prior to the current MI diagnosis are excluded. In Katz et al. (2014), for both indicators, patients diagnosed within the past three years with a diagnosis of AMI (ICD-9-CM = 410 or ICD-10-CA = I21 or I22) were excluded.

The following list of research provides links to the findings relevant to post-MI management with cholesterol lowering drug treatment:


• In Katz et al. (2004), they investigate the rates of patients who had a cholesterol screening test within four months of discharge for Winnipeg family physicians (FPs) only. See section 3.3.8 Post-Myocardial Infarction Care: Cholesterol Testing for more information.
  
  
• In Katz et al. (2010), they compare the prevalence rates of these two indicators for four different groups of patients related to the implementation of Physician Integrated Network (PIN) clinics. See the section titled Post-Myocardial Infarction (MI) Care: Treatment with Cholesterol-Lowering Drugs for more information.
  
  
• In Katz et al. (2014), they compare the rates of these two indicators related to the implementation of Physician Integrated Network (PIN) clinics. See the section titled Post Myocardial Infarction Management: Initiation and Persistence of Cholesterol Lowering Drug Treatment for more information.