Classification of Myocardial Infarction: Frequency and Features of Type 2 Myocardial Infarction
What are the frequency and characteristics of type 2 myocardial infarction?
This was a prospective study of 1,000 unselected patients who had cardiac troponin I (cTnI) measured on admission. The frequency and features of type 2 myocardial infarction were investigated with the use of novel developed criteria that included conditions reflecting an imbalance between myocardial oxygen supply and demand. Conditions with decreased oxygen supply were: anemia, shock, certain bradyarrhythmias, coronary embolus in the presence of an increased risk of embolism, and respiratory failure. Conditions with increased oxygen demand were: certain ventricular tachyarrhythmias, certain supraventricular tachyarrhythmias, hypertensive pulmonary edema, and arterial hypertension (systolic blood pressure >160 mm Hg) with echocardiographic evidence of left ventricular hypertrophy.
Among 4,499 patients who qualified for inclusion, the diagnosis of myocardial infarction was established in 553 patients, of whom 386 (72%) had a type 1 myocardial infarction and 144 (26%) had a type 2 myocardial infarction. Anemia, tachyarrhythmias, and respiratory failure were the most prevalent conditions underlying type 2 myocardial infarction. Approximately half of patients with type 2 myocardial infarction did not have significant coronary artery disease on angiography. Patients with type 2 myocardial infarction had more comorbidities (heart failure, renal failure, chronic obstructive pulmonary disease, and arrhythmias).
In unselected hospital patients, one fourth of all myocardial infarctions are type 2, and approximately half of such patients with type 2 myocardial infarction do not have significant coronary artery disease.
This prospective study is a step forward in characterizing the frequency and characteristics of type 2 myocardial infarction. By applying clinical criteria developed by their own study group, the authors have demonstrated that type 2 myocardial infarction is frequent, associated with comorbidities, and frequently develops in the absence of angiographically significant coronary artery disease. Future studies should build on these findings and make progress toward establishing an accepted standard defining type 2 myocardial infarction.
Keywords: Pulmonary Edema, Myocardial Infarction, Biological Markers, Troponin I, Heart Failure, Blood Pressure, Hypertension, Echocardiography, Lung Diseases
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