An acute myocardial infarction (MI), colloquially known as a heart attack, is a medical emergency related to an imbalance of oxygen supply and demand due to the heart not functioning properly. Acute MI, which is classified into three types, is when there is acute myocardial injury with clinical evidence of acute myocardial ischemia and with detection of a rise and/or fall of cardiac troponin (cTn) values with at least one value above the 99th percentile upper reference limit (URL) and at least one of the following:1,2
- Symptoms of myocardial ischemia
- New ischemic echocardiogram (ECG) changes
- Development of pathological Q waves
- Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality in a pattern consistent with an ischemic etiology
- Identification of a coronary thrombus by angiography or autopsy (not for type 2 or 3 MIs)
The classification for acute MI type are as follows:1
- Type 1 – Caused by atherothrombotic coronary artery disease and usually precipitated by atherosclerotic plaque disruption (rupture or erosion).
- Type 2 – The pathophysiological mechanism leading to ischemic myocardial injury in the context of a mismatch between oxygen supply and demand. Acute atherothrombotic plaque disruption is not a feature of type 2 MI. An acute stressor such as a precipitous drop in hemoglobin or sustained tachyarrhythmia may result in a type 2 MI.
- Type 3 – When suspicion for an acute myocardial ischemic event is high even though there is no cardiac biomarker evidence due to loss of life before blood can be drawn. This category allows the separation of fatal MI events from sudden death. Type 3 MIs can be reclassified as type 1 after autopsy reveals further evidence of thrombus in the infarct-related artery.
Myocardial ischemia is the initial step in the development of MI.2 In the clinical setting, it can most often be identified from a patient’s health history and from the ECG. Possible ischemic symptoms include various combinations of chest, upper extremity, mandibular, or epigastric discomfort, or an ischemic equivalent such as dyspnea or fatigue.3,4 These symptoms can occur during exertion or at rest, although they typically worsen with exertion. Often the discomfort is diffuse, not localized, positional, or affected by movement of the area. However, these symptoms are not specific to MIs and can be caused by other gastrointestinal, neurological, pulmonary, or musculoskeletal conditions. MIs may also cause atypical symptoms such as palpitations or cardiac arrest, or even no symptoms at all.
There are several potential differences between symptom presentation in men and women: men are more likely to present with chest pain or sweating while women are more likely to present with radiating pain to one or both arms, neck, or back, nausea and vomiting, heartburn or indigestion, and shortness of breath. One study examining MI presentation (n= 1,143,513) found that 42.0% of men presented with chest pain (95% confidence interval [CI] [41.8%-42.1%]) while only 30.7% of women did (95% CI [30.6-30.8]).5 Another study of 455 patients (332 men and 123 women) with acute MI in the hospital setting found that women were more likely than men to have right arm pain (42% vs 32%), left arm pain (58% vs 48%), neck pain (37% vs 24%), and back pain (38% vs 22%).6 Another study (n=895, 36% women) found that compared with men, women were more likely to have nausea (40% vs 30%), vomiting (24% vs 11%), and shortness of breath (63% vs 51%) and were less likely to have chest pain (84% vs 90%).7 The prevalence of abdominal pain, dizziness, and fainting was similar between men and women. Another study of 4,497 patients (34% women) found that women were more likely to report nausea or vomiting (44% vs 35%) and shortness of breath (52% vs 46%) but less likely to report sweating (44% vs 54%).8 Another study (n=217, 90 women) found that women were more likely to experience indigestion (22% vs 12%).9
The duration of symptoms directly impacts the likelihood of survival. Most deaths associated with acute MIs occur within the first hour of its onset.1,10 While there are life-saving treatments that can help those who have suffered an acute MI, most are only effective within the first several hours of onset. Thrombolytic or clot dissolving drugs such as tissue plasminogen activator (tPA), Streptokinase, or Urokinase can be injected to dissolve arterial blockage within three hours of the onset of an acute MI, with effectiveness of treatment dropping off after 6 hours post-onset.3,11 Thus, it is important to seek help immediately if someone suspects they are having an acute MI.
- Thygesen K, Alpert J, Jaffe A, et al.1J Am Coll Cardiol. 2018;(72):2231-2264.
- Scirica B, Peter L, Morrow D. ST-Elevation Myocardial Infarction: Pathophysiology and Clinical Evolution. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 12 ed. Elsevier; 2021:636-661:chap 37.
- Lu L, Liu M, Sun R, Zheng Y, Zhang P. Myocardial Infarction: Symptoms and Treatments. Cell Biochemistry and Biophysics. 2015;(72):865-867. doi:10.1007/s12013-015-0553-4
- Constant J. The clinical diagnosis of nonanginal chest pain: the differentiation of angina from nonanginal chest pain by history. Clin Cardiol. Jan 1983;6(1):11-6. doi:10.1002/clc.4960060102
- Canto JG, Rogers WJ, Goldberg RJ, et al. Association of age and sex with myocardial infarction symptom presentation and in-hospital mortality. Jama. Feb 22 2012;307(8):813-22. doi:10.1001/jama.2012.199
- Everts B, Karlson B, Warborg P, Hedner T, Herlitz J. Localisation of pain in suspected myocardial infarction in relation to final diagnosis, age, sex and type of infarction. Heart & Lung. 1996;25(6):430-437.
- Maynard C, Beshansky J, Griffith J, Selker H. Influence of sex on the use of cardiac procedures in patients presenting to the emergency department: A prospective multicenter study. Circulation. 1996;94(9):93-98.
- Meischke H, Larsen M, Eisenberg M, Mickey S. Gender differences in reported symptoms for acute myocardial infarction: impact on prehospital delay time interval. Am J Emerg Med. 1998;16(4):363-366.
- Milner K, Funk M, Richards S, Wilmes R, Vaccarino V, Krumholz H. Gender differences in symptom presentation associated with coronary heart disease. The American journal of cardiology. 1999;84(4):396-399.
- Bohula E, Morrow D. ST-Elevation Myocardial Infarction: Management. Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine. 12 ed. 2021:662-713:chap 38.
- Emergency department: rapid identification and treatment of patients with acute myocardial infarction. National Heart Attack Alert Program Coordinating Committee, 60 Minutes to Treatment Working Group. Ann Emerg Med. Feb 1994;23(2):311-29.