eMedicine Specialties > Cardiology > Coronary Artery Disease

Myocardial Infarction

Author: Samer Garas, MD, FACC, Chief of Cardiology, Department of Interventional Cardiology, St Vincent's Hospital
Coauthor(s): A Maziar Zafari, MD, PhD, FACC, Associate Professor, Department of Medicine, Emory University School of Medicine; Chief, Section of Cardiology, Atlanta Veterans Affairs Medical Center
Contributor Information and Disclosures

Updated: Jan 22, 2010

Introduction

Background

Myocardial infarction (MI) is the irreversible necrosis of heart muscle secondary to prolonged ischemia. This usually results from an imbalance of oxygen supply and demand. The appearance of cardiac enzymes in the circulation generally indicates myocardial necrosis. Myocardial infarction is considered, more appropriately, part of a spectrum referred to as acute coronary syndromes (ACSs), which also includes unstable angina and non–ST-elevation MI (NSTEMI). Patients with ischemic discomfort may or may not have ST-segment elevation. Most of those with ST-segment elevation will develop Q waves. Those without ST elevations will ultimately be diagnosed with unstable angina or NSTEMI based on the presence of cardiac enzymes.

Myocardial infarction may lead to impairment of systolic function or diastolic function and to increased predisposition to arrhythmias and other long-term complications.

Pathophysiology

Atherosclerosis is the disease primarily responsible for most acute coronary syndrome cases. Approximately 90% of myocardial infarctions result from an acute thrombus that obstructs an atherosclerotic coronary artery. Plaque rupture is considered to be the major trigger of coronary thrombosis. Following plaque rupture, platelet activation and aggregation, coagulation pathway activation, and endothelial vasoconstriction occur and lead to coronary thrombosis and occlusion.

Consider nonatherosclerotic causes of acute myocardial infarctions in younger patients or if no evidence of atherosclerosis is noted. Such causes include coronary emboli from sources such as an infected cardiac valve through a patent foramen ovale (PFO), coronary occlusion secondary to vasculitis, primary coronary vasospasm (variant angina), cocaine use, or other factors leading to mismatch of oxygen supply and demand, as may occur with a significant gastrointestinal bleed.

Frequency

United States

Approximately 1.5 million cases of myocardial infarction occur each year.

International

Cardiovascular diseases cause 12 million deaths throughout the world each year, according to the third monitoring report of the World Health Organization, 1991-93. They cause half of all deaths in several developed countries and are one of the main causes of death in many developing countries; they are the major cause of death in adults everywhere.

Mortality/Morbidity

  • Cardiovascular disease is the leading cause of death in the United States; approximately 500,000-700,000 deaths related to the coronary artery occur each year.
  • Ischemic heart disease is the leading cause of death worldwide.
  • Approximately 6.3 million deaths due to heart disease occurred in 1990 worldwide, which represents 29% of all deaths. The prevalence of coronary artery disease (CAD) is increasing rapidly in nonindustrialized countries.
  • Beck et al found that elevated blood glucose level on admission is associated with increased short-term mortality in nondiabetic patients presenting with a first acute myocardial infarction. Analysis of data from a German myocardial infarction registry database showed that among 1,631 nondiabetic acute myocardial infarction patients with admission glucose level more than 152 mg/dL (top quartile), the risk of death within 28 days was higher than among those in the bottom quartile (odds ratio, 2.82; 95% confidence interval, 1.30-6.12). However, in 659 registry patients with type 2 diabetes, admission glucose levels did not correlate significantly with short-term mortality. Beck et al conclude that nondiabetic acute myocardial infarction patients with elevated glucose levels constitute a high-risk group that requires aggressive intervention.1

Race

Cardiovascular disease is the leading cause of morbidity and mortality among African American, Hispanic, and white populations in the United States.

Sex

  • A male predominance in incidence exists up to approximately age 70 years, when the sexes converge to equal incidence.
  • Premenopausal women appear to be somewhat protected from atherosclerosis, possibly owing to the effects of estrogen.

Age

  • Incidence increases with age.
  • Most patients who develop an acute myocardial infarction are older than 60 years. Elderly people also tend to have higher rates of morbidity and mortality from their infarcts.

Clinical

History

Symptoms of myocardial infarction include the following:

  • Chest pain
    • This is usually described as a substernal pressure sensation that also may be described as squeezing, aching, burning, or even sharp pain.
    • Prolonged chest discomfort lasting longer than 30 minutes is most compatible with infarction.
    • Radiation to the left arm or neck is common.
    • The sensation is precipitated by exertion and relieved by rest and nitroglycerin.
    • Chest pain may be associated with nausea, vomiting, diaphoresis, dyspnea, fatigue, or palpitations.
    • Atypical chest pain is common, especially in patients with diabetes and in elderly patients. However, any patient may present with atypical symptoms. These symptoms are considered the anginal equivalent for that patient.
  • Shortness of breath
    • Shortness of breath may be the patient's anginal equivalent or a symptom of heart failure.
    • It is due to elevated end-diastolic pressures secondary to ischemia, which may then lead to elevated pulmonary pressures.
  • Atypical presentations
    • 20% of patients are asymptomatic or have atypical symptoms.
    • Atypical presentations are common and frequently lead to misdiagnoses.
    • A patient may, for example, present with abdominal discomfort or jaw pain as his or her anginal equivalent.
    • An elderly patient may present with altered mental status.
    • Low threshold should be maintained when evaluating high- and moderate-risk patients, as their anginal equivalents may mimic other presentations.
    • Women tend to present more commonly with atypical symptoms such as sharp pain, fatigue, weakness, and other nonspecific complaints.

Physical

Physical examination findings for myocardial infarction can vary; one patient may be comfortable in bed, with normal examination results, while another may be in severe pain with significant respiratory distress requiring ventilatory support.

  • Low-grade fever may be present.
  • Hypotension or hypertension can be observed depending on the extent of the myocardial infarction.
  • Fourth heart sound (S 4 ) may be heard in patients with ischemia. With ischemia, diastolic dysfunction is the first physiologically measurable effect and this can then cause a stiff ventricle and an audible S 4 .
  • Dyskinetic cardiac bulge (in anterior wall myocardial infarction) can occasionally be palpated.
  • Systolic murmur can be heard if mitral regurgitation (MR) or ventricular septal defect (VSD) develops.
  • Other findings include cool, clammy skin and diaphoresis.
  • Signs of congestive heart failure (CHF) may be found, including the following:
    • Third heart sound (S 3 ) gallop
    • Pulmonary rales
    • Lower extremity edema
    • Elevated jugular venous pressure

Causes

  • Atherosclerosis with occlusive or partially occlusive thrombus formation
  • Nonmodifiable risk factors for atherosclerosis
    • Age
    • Sex
    • Family history of premature coronary heart disease
  • Modifiable risk factors for atherosclerosis
    • Smoking or other tobacco use
    • Diabetes mellitus
    • Hypertension
    • Dyslipidemia
    • Obesity
  • New and other risk factors for atherosclerosis
    • Elevated homocysteine levels
    • Male pattern baldness
    • Sedentary lifestyle and/or lack of exercise
    • Psychosocial stress
    • Presence of peripheral vascular disease
    • Poor oral hygiene
  • Nonatherosclerotic causes
    • Vasculitis
    • Coronary emboli
    • Congenital coronary anomalies
    • Coronary trauma
    • Coronary spasm
    • Drug use (cocaine)
    • Factors that increase oxygen requirement, such as heavy exertion, fever, or hyperthyroidism
    • Factors that decrease oxygen delivery, such as hypoxemia of severe anemia

More on Myocardial Infarction

Overview: Myocardial Infarction
Differential Diagnoses & Workup: Myocardial Infarction
Treatment & Medication: Myocardial Infarction
Follow-up: Myocardial Infarction
Multimedia: Myocardial Infarction
References
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References

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Further Reading

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Keywords

myocardial infarction, heart attack, acute coronary syndromes, ACS, MI, unstable angina, non–ST-elevation MI, NSTEMI, coronary artery disease, CAD, ischemic heart disease, chest pain, impaired systolic function, impaired diastolic function, myocardial necrosis, atherosclerosis, coronary thrombus, plaque rupture, coronary emboli, infected cardiac valve, coronary occlusion secondary to vasculitis, primary coronary vasospasm, variant angina

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Contributor Information and Disclosures

Author

Samer Garas, MD, FACC, Chief of Cardiology, Department of Interventional Cardiology, St Vincent's Hospital
Samer Garas, MD, FACC is a member of the following medical societies: Alpha Omega Alpha, American College of Cardiology, and American Medical Association
Disclosure: Nothing to disclose.

Coauthor(s)

A Maziar Zafari, MD, PhD, FACC, Associate Professor, Department of Medicine, Emory University School of Medicine; Chief, Section of Cardiology, Atlanta Veterans Affairs Medical Center
A Maziar Zafari, MD, PhD, FACC is a member of the following medical societies: American Association for the Advancement of Science, American College of Cardiology, American Heart Association, American Society of Echocardiography, and Association of Professors of Medicine
Disclosure: Nothing to disclose.

Medical Editor

Eric Vanderbush, MD, FACC, MD, Chief, Department of Internal Medicine, Division of Cardiology, Clinical Assistant Professor, Harlem Hospital Center and Columbia University
Eric Vanderbush, MD, FACC, MD is a member of the following medical societies: American College of Cardiology and American Heart Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Marschall S Runge, MD, PhD, Charles and Anne Sanders Distinguished Professor of Medicine, Chairman, Department of Medicine, Vice Dean for Clinical Affairs, University of North Carolina at Chapel Hill School of Medicine
Marschall S Runge, MD, PhD is a member of the following medical societies: American Association for the Advancement of Science, American College of Cardiology, American College of Physicians-American Society of Internal Medicine, American Federation for Clinical Research, American Federation for Medical Research, American Heart Association, American Physiological Society, American Society for Clinical Investigation, American Society for Investigative Pathology, Association of American Physicians, Association of Professors of Cardiology, Association of Professors of Medicine, Southern Society for Clinical Investigation, and Texas Medical Association
Disclosure: Pfizer Honoraria Speaking and teaching; Merck Honoraria Speaking and teaching; Orthoclinica Diagnostica Consulting fee Consulting

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Eric H Yang, MD, Assistant Professor of Medicine, Director of Coronary Care Unit, University of North Carolina at Chapel Hill School of Medicine
Eric H Yang, MD is a member of the following medical societies: Alpha Omega Alpha
Disclosure: Up to Date Royalty Review panel membership

 
 
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