Acute Myocardial Infarction and Ischemia

Acute myocardial infarction (MI) accounts for 650,000 hospital admissions each year and is one of the leading causes of death in the United States. A missed diagnosis of MI can have fatal or debilitating consequences. Furthermore, a missed diagnosis of MI is the most common and most costly cause of malpractice litigation. Reasons for a missed diagnosis of MI include failure to consider the diagnosis in an atypical presentation, misinterpreting or not ordering appropriate tests (such as an ECG), or inappropriately relying on a single, normal ECG or serum marker for MI to rule out infarction.

Epidemiologic risk factors for coronary artery disease include history of hypertension, diabetes, smoking, elevated serum cholesterol, male sex, age over 40, and family history of premature coronary artery disease. However, these do not effectively predict acute ischemia in the ED. The most important diagnostic factors in the ED are (I) symptoms consistent with MI, (2) past history of ischemic heart disease, and (3) an abnormal ECG (see below). Up to one half of patients have unstable angina before MI. Cocaine abuse can induce ischemia in younger individuals who have no other risk factors.

Causes

Causes include the following:

• Coronary artery emboli, secondary to cholesterol, air, or the products of sepsis
• Cocaine, amphetamines, and ephedrine
• Coronary artery vasospasm
• Ventricular hypertrophy
• Increased afterload, which increase the demand on the myocardium
• Risk factors for atherosclerotic plaque formation include the following:
  • Age
  • Smoking
  • Diabetes mellitus
  • Family history
  • Hypercholesterolemia and hypertriglyceridemia, including inherited lipoprotein disorders

Symptoms

• Chest pain ++++ in acute MI or ischemia is typically heavy, squeezing, tight, or pressure-like in quality, but may be sharp ++, burning, or indigestion-like ++, pleuritic +, or even absent.
• Painless MI is more common in the elderly and in patients with diabetes. The frequency of chest pain decreases steadily after age 65 to 70 and is present in only 50% at age 80, after which dyspnea is the most common symptom. 'Pain typically localizes to the retrosternal area or, less often, the left chest. It may localize to the epigastrium or back. It may radiate to, or even primarily localize to, the arm, shoulder(s), jaw, or neck +++. The pain usually is not positional +. The upper limit of constant pain duration is difficult to define but is usually measured in hours, not days.
• Dyspnea
• Diaphoresis +++
• Nausea +++
• Dizziness
• Palpitations
• Apprehension
• Syncope
• Sudden death

Signs

• Tachycardia (+++ anterior MIs)
• Bradycardia (+++ inferior MIs)
• Diaphoresis ++
• Premature beats
• Hypertension or hypotension
• Vomiting
• Murmurs; a new murmur with pathologic qualities may indicate papillary muscle dysfunction or rupture (producing mitral regurgitation) or perforation of the interventricular septum.
• Gallops
• Rales
• Altered mental status
• Evidence of peripheral vascular disease (e.g., diminished pedal pulses, femoral bruits, or claudication) also increases the likelihood of coronary artery disease.
• Signs of cerebral ischemia may coexist in 10% of elderly patients.

Treatment

A heart attack, especially because of cardiac arrhythmias, is often a life-threatening medical emergency which demands both immediate attention and activation of the emergency medical services. Immediate termination of arrhythmias and transport by ambulance to a hospital where advanced cardiac life support is available can greatly improve both chances for survival and recovery. The more time that passes, even 1 – 2 minutes, before medical attention is available, the more likely the occurrence of both

(a) life threatening arrhythmias/death

(b) more severe and permanent heart damage.