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Myocardial infarction

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Myocardial infarction is the main cause of death in Western societies (1).

Myocardial infarction is considered as part of a spectrum referred to as acute coronary syndrome, which refers to a range of acute myocardial ischaemia that also includes unstable angina and non-ST segment elevation myocardial infarction (NSTEMI).

  • the criteria for diagnosing myocardial infarction are detection of rise and/or fall of cardiac biomarkers (preferably troponin) with at least one value above the 99th percentile of the upper reference limit, together with evidence of myocardial ischaemia with at least one of the following (2)
    • symptoms of ischaemia
    • electrocardiogram (ECG) changes indicative of new ischaemia (new ST-T changes or new left bundle branch block (LBBB))
    • development of pathological Q wave changes in the ECG
    • imaging evidence of new loss of viable myocardium or new regional wall motion abnormality

A myocardial infarction that has associated ST elevation is defined as a STEMI (ST segment elevation myocardial infarction). Before the use of the term acute coronary syndrome (and use of more sensitive cardiac markers such as troponin), this was what was previously diagnosed as a myocardial infarction.

  • ST-segment-elevation myocardial infarction (STEMI) occurs when a coronary artery becomes blocked by a blood clot, causing the heart muscle supplied by the artery to die (3)
    • incidence of STEMI has been declining over the past 20 years. It varies between regions and averages around 500 hospitalised episodes per million people each year in the UK.
      • the London Ambulance Service attended 9657 cardiac arrests in 2011-12 for a population of around 8.2 million people (1177 per million people). Most of these will have been attributed to acute coronary syndromes, so the overall population prevalence of STEMI is likely to be in the region of 750-1250 per million people
      • over the past 30 years, in-hospital mortality after acute coronary syndromes has fallen from around 20% to nearer 5%. This has been attributed to various factors, including improved drug therapy and speed of access to effective treatments
    • nearly half of potentially salvageable myocardium is lost within 1 hour of the coronary artery being occluded, and two-thirds are lost within 3 hours. Apart from resuscitation from any cardiac arrest, the highest priority in managing STEMI is to restore an adequate coronary blood flow as quickly as possible.

About 30% of people who die of a myocardial infarction do so before reaching hospital (4).

A study investigating one-year mortality following diagnosis of acute coronary syndrome showed (1):

  • mortality rate was 3.9% within one year of discharge
    • independent mortality predictors identified (in order of predictive strength):
      • age, lower ejection fraction, poorer EQ-5D quality of life, elevated serum creatinine, in-hospital cardiac complications, chronic obstructive pulmonary disease, elevated blood glucose, male gender, no PCI/CABG after NSTEMI, low hemoglobin, peripheral artery disease, on diuretics at discharge

A study investigating two-year mortality following diagnosis of acute coronary syndrome showed (2):

  • mortality rate was 5.5% within two years of discharge
    • independent mortality predictors identified were:
      • age, low ejection fraction, no coronary revascularization/thrombolysis, elevated serum creatinine, poor EQ-5D score, low haemoglobin, previous cardiac or chronic obstructive pulmonary disease, elevated blood glucose, on diuretics or an aldosterone inhibitor at discharge, male sex, low educational level, in-hospital cardiac complications, low body mass index, ST-segment elevation myocardial infarction diagnosis, and Killip class

Data from a large Swedish registry including 108 315 post-MI patients with long-term follow-up revealed a cumulative rate of a cardiovascular composite endpoint (cardiovascular death, recurrent MI, and stroke) of 18.3% in the first year after MI, 9.0% in the subsequent year and 20.0% in the following 3 years (7)

Myocardial infarction accounts for one third of the mortality which can be attributed to coronary artery disease. Atheromatous coronary artery disease is almost always the cause of myocardial infarction.

Cardiogenic shock occurs in up to 10% of patients immediately following acute myocardial infarction and is associated with mortality rates of nearly 40% at 30 days and 50% at 1 year (8).


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