Date Published: July 12, 2017
Publisher: Public Library of Science
Author(s): Navdeep Tangri, Thomas W. Ferguson, Reid H. Whitlock, Claudio Rigatto, Davinder S. Jassal, Malek Kass, Olga Toleva, Paul Komenda, Jianzhong Sun.
Myocardial infarction (MI) is associated with high morbidity and mortality, particularly in the first 12 months post-event. Interventions such as dual antiplatelet therapy can reduce the risk of major adverse cardiovascular events (MACE), but the duration of the high-risk time interval and the optimal prescription time frame for these interventions remains unknown.
We performed a retrospective cohort study using data from medical services and hospitalizations in Manitoba, Canada for patients admitted with a MI between April 2006 and March 2010, and followed until Nov 30, 2014. We used survival analysis to determine the cumulative incidence of death, subsequent MI, or stroke, and used Cox proportional hazards models to assess factors associated with these endpoints.
There were 8,493 patients in Manitoba admitted to hospital for a MI during the study period. Of those, 6,749 (79.5%) survived for at least 1 year without a recurrent MI or stroke. In the following year, this population remained at high risk, with 372 (5.5%) of the remaining patients dying in the next twelve months (48.1% cardiovascular deaths), 244 (3.6%) having a recurrent MI, and 74 (1.1%) having a stroke. Older age, male sex, diabetes, prior stroke, prior heart failure, prior unstable angina, and absence of revascularization were associated with worse long-term prognosis.
The risk of MACE remains elevated among post-MI patients after the first year. Interventions to more intensively monitor, evaluate, and treat these patients should be considered beyond the first year following myocardial infarction.
Cardiovascular (CV) disease causes one-third of deaths in Canada, more than any other illness, and is associated with a high economic burden on the health care system . Myocardial infarction (MI), a consequence of CV disease, is associated with significant morbidity and mortality . Despite improvements in acute therapy, and better risk factor control, recurrence rates of major adverse cardiovascular events (MACE), including MI, stroke, and/or death remain high, affecting nearly 1 in 5 patients in the first year post discharge and another 1 in 5 patients over the next 3 years [2–4]. An aging population and increase in obesity rates further threatens to sustain these high rates of MI and CV disease along with their associated adverse events .
We performed an observational, retrospective cohort study that analyzed patient level data obtained by linking several provincial registries from Manitoba, Canada housed at the Manitoba Centre for Health Policy (MCHP) . These databases included: the Manitoba Health Insurance Registry (patient registry and dates of coverage), Vital Statistics (date and cause of death), Medical Services (physician claims), Canadian Institute for Health Information (CIHI) Discharge Abstract Database (DAD) (hospital admission data), Diagnostic Services of Manitoba (DSM) (laboratory diagnostics), and the Drug Program Information Network (DPIN) database (drug prescriptions). Supplemental information on data availability is available in S1 File. We determined all primary and secondary diagnoses using ICD-9-CM and ICD-10-CM codes in both hospital discharge abstracts and medical services claims (S1 Table). All drugs were classified according to the Anatomical Therapeutic Chemical system (S2 Table). This study received ethics approval from the University of Manitoba Health Research Ethics Board (ethics file number HS18939).
In this provincial cohort study of patients who survived their index MI, nearly one in four patients reached the clinical endpoint of stroke, recurrent MI, or death in the first 365 days after the index event. Older age, diabetes, prior heart failure and absence of revascularization were associated with a poor prognosis in the first year post discharge. For patients who survived for 12 months without a subsequent MI event or stroke (the early event free post-MI population), one in ten experienced an event within the following year with a mortality rate exceeding 5%. Although this early event free post-MI population was at lower risk of an event when compared to the entire MI population, the mortality risk is still substantial and higher than risk thresholds for DAPT proposed by the American Heart Association and European Society of Cardiology guidelines [11, 12].
The risk of adverse events remains consistently elevated among MI patients in the years following their index MI event. Interventions to more intensively monitor, evaluate, and treat these patients should be considered beyond the first year following myocardial infarction.