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Definition of Type 2 Myocardial Infarction
Study Questions:
How does the definition of type 2 myocardial infarction (T2MI) impact incidence, treatment, and T2MI-related mortality?
Methods:
In 4,015 consecutive patients, the diagnosis of T2MI was determined by two cardiologists by two methods: 1) MI secondary to ischemia with known or newly diagnosed coronary artery disease (CAD), following the 2007 universal definition of T2MI (T2MI2007); and 2) using the 2012 universal definition (T2MI2012), which did not require the presence of CAD. Patients with end-stage renal disease on dialysis and patients with an unclear diagnosis after adjudication were excluded. All patients had levels of cardiac troponins at presentation and as deemed clinically necessary, and adjudication encompassed all available medical records from the time of presentation to 90-day follow-up. MI was diagnosed when there was evidence of myocardial necrosis in association with a clinical setting consistent with myocardial ischemia. Presence of CAD was adjudicated based on a history of type 1 MI, history of coronary revascularization, coronary angiography or computed tomography (CT) angiography showing a coronary artery diameter ≥50%, cardiac imaging showing a myocardial scar, or cardiac imaging documenting inducible myocardial ischemia. The primary endpoint was cardiovascular mortality at 90 days. The use of coronary revascularization, dual antiplatelet therapy, and high-dose statins was assessed at hospital discharge.
Results:
From April 2006 to August 2015, 4,015 patients were included. The incidence of T2MI by T2MI2007 definition was 2.8% (112 patients) and 6% (240 patients) by the T2MI2012 definition, a relative increase of 114%. Major mechanisms for reclassification as T2MI based on T2MI2012 definition were bradyarrhythmias, tachyarrhythmias, hypertensive crisis, severe anemia, and respiratory failure. Compared to patients with T2MI by T2MI2007 criteria, those patients reclassified as T2MI by T2MI2012 (n = 128, T2MI2012reclassified) were younger, more often female, and had lower rates of cardiovascular risk factors and previous cardiovascular disease. Among T2MI2007, 6.3% received coronary revascularization, 22% dual antiplatelet therapy, and 71% high-dose statin, versus 0.8%, 1.6%, and 31% among T2MI2012reclassified. There were no deaths within 90 days among the 128 T2MI2012reclassified patients, compared with four deaths (3.7%) among patients with T2MI2007. Death rates for T2MI2012reclassified were similar to patients with noncardiac causes of chest pain and myocardial injury from other causes.
Conclusions:
Patients reclassified with T2MI based on T2MI2012 criteria have lower cardiovascular mortality compared to patients with T2MI based on T2MI2007 criteria.
Perspective:
A major difference in the definition of T2MI is that T2MI2007 requires the presence of CAD, whereas T2MI2012 includes patients who suffer myocardial injury from non-CAD causes (e.g., coronary endothelial dysfunction, coronary artery spasm, coronary embolism, tachy- and/or bradyarrhythmias, anemia, respiratory failure, hypotension, and hypertension). This study demonstrates several key points. The more liberal T2MI2012 definition increased the incidence of T2MI. Patients reclassified with T2MI (from T2MI2007 to T2MI2012) had a lower prevalence of pre-existing cardiovascular disease and this population rarely underwent coronary revascularization (<1%). Cardiovascular mortality in T2MI2012reclassified patients had a mortality rate similar to patients with other causes of chest discomfort and myocardial injury. Further studies are required to develop evidenced-based treatment strategies for T2MI, especially relating to the use of dual antiplatelet therapy and high-intensity statins.
Keywords: Acute Coronary Syndrome, Anemia, Bradycardia, Cardiovascular Diseases, Chest Pain, Coronary Angiography, Coronary Artery Disease, Embolism, Heart Failure, Hydroxymethylglutaryl-CoA Reductase Inhibitors, Kidney Failure, Chronic, Myocardial Infarction, Myocardial Ischemia, Myocardial Revascularization, Myocardium, Platelet Aggregation Inhibitors, Primary Prevention, Respiratory Insufficiency, Risk Factors, Tachycardia, Troponin
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