During the last 4 decades, the epidemiologic characteristics of acute myocardial infarction have changed.
Recently, Jeffrey Anderson, MD, of the Intermountain Medical Center Heart Institute, and David Morrow, MD, of Brigham and Women’s Hospital, have reviewed how initial presentation and in-hospital management of type I acute myocardial infarction, with or without ST-segment elevation, is handled.
Definition and Types
The authors define acute myocardial infarction as “an event of myocardial necrosis caused by an unstable ischemic syndrome,” and add that clinical evaluation, an electrocardiogram (ECG), imaging, biochemical testing, and a pathological evaluation are additional steps in diagnosing the disorder.
Acute myocardial infarction is divided into 2 broad categories: the absence or presence of ST-segment elevation according to the ECG. There are 6 additional classifications.
During the last 30 to 40 years, the epidemiologic characteristics of acute myocardial infarction have changed. Incidence has declined, but there are still around 550,000 first episodes and 200,000 recurrent episodes per year.
Low- to middle-income countries bear the greatest burden of cardiovascular disease, with 80% of deaths globally occurring in those countries. Income is directly related to risk, with more risk in higher income countries. However, the authors note, “an inverse relationship was noted for rates of acute myocardial infarction.” It is likely that more preventative measures are taken in higher-income countries and that offsets the greater risk burden.
Usually, acute myocardial infarction happens when an atherosclerotic coronary plaque, which is lipid-laden and vulnerable, ruptures or erodes. Lipid-lowering therapies have led to erosion being the underlying cause more often than rupture. About 10% of cases of acute myocardial infarction occur in the absence of critical epicardial coronary disease.
Initial Medical Evaluation and Risk Assessment
Patients may have chest discomfort, dyspnea, unexplained weakness, or a combination of those symptoms and should be referred to an emergency department if acute myocardial infarction is suspected. Following an ECG, which should be performed within 10 minutes of the patient’s arrival, blood should be taken and rapid diagnostic triage performed.
The authors say that 2 risks should be assessed: the risk that the problem is an acute coronary syndrome, and the risk of an early adverse outcome. There are 2 validated models for assessing those risks, the Thrombolysis in Myocardial Infarction (TIMI) and the Global Registry of Acute Coronary Events (GRACE) models.
Initial Medical Care
The authors discuss prehospital care, which is a major factor in morbidity and mortality, and emergency department and early inpatient care, which make up the initial management of acute coronary syndromes. Prehospital care should include a rapid assessment, initiation of treatment, and transportation to a hospital at the minimum. Additional steps, such as an ECG and STEMI diagnosis, can lead to superior outcomes.
Bed rest and beginning antithrombotic therapy make up the initial management of acute coronary syndromes. According to the authors, “The severity of the symptoms dictates other features of general care.”
Although it is routine in most places to supplement oxygen, evidence does not support its use unless the patient has lower than normal oxygen levels or is in respiratory distress. Sublingual nitroglycerin, beta-blocker therapy, angiotensin-converting-enzyme (ACE) inhibitors, and aldosterone inhibitors may be indicated, depending on the patient.
Selection of a Management Strategy
The management strategy in acute myocardial infarction cases depends in large part on whether or not the ECG indicates ST-segment elevation. Treatment of STEMI has advanced in the last 30 years, thanks to emergency reperfusion of ischemic myocardium that is in the process of becoming infarcted. It is the preferred approach in PCI capable hospitals when the onset of symptoms is within 12 hours.
The authors do note, “An ongoing controversy in the use of PCI for STEMI is the approach to stenoses in nonculprit coronary arteries,” and add that large, randomized trials are needed.
In cases without ST-segment elevation, there are 2 strategies, either an invasive strategy or an ischemia-guided strategy. The authors say that an invasive strategy is favored by most patients and has better outcomes. Sometimes initial medical therapy allows for a slightly delayed approach of 12 to 24 hours, and some patients may be able to wait 25 to 72 hours for an angioplasty. Patients with a low risk of recurrent ischemia or where interventional services are unavailable may need an ischemia-guided strategy.
The authors suggest that adherence to evidence-based guidelines, as well as improving how those guidelines are translated into routine practice, are going to be the best way to improve fatality rates among patients with acute myocardial infarction. The full review can be found in The New England Journal of Medicine.