Myocardial infarction
LIFE-THREATENING DISORDERWith myocardial infarction (MI), also known as heart attack, reduced blood flow through one of the coronary arteries results in myocardial ischemia and necrosis. With cardiovascular disease, the leading cause of death in the United States and western Europe, death usually results from the cardiac damage or complications of an MI.
Mortality is high when treatment is delayed; almost half of all sudden deaths due to an MI occur before hospitalization, within 1 hour of the onset of symptoms. The prognosis improves if vigorous treatment begins immediately.
Causes
Predisposing factors include:
positive family history
hypertension
smoking
elevated levels of serum triglycerides, total cholesterol, and low-density lipoproteins
diabetes mellitus
obesity or excessive intake of saturated fats, carbohydrates, or salt
sedentary lifestyle
aging
stress or a type A personality (aggressive, ambitious, competitive, addicted to work, chronically impatient)
drug use, especially cocaine.
Men and postmenopausal women are more susceptible to an MI than premenopausal women, although incidence is rising among females, especially those who smoke and take a hormonal contraceptive. (See MI in women.)
The site of the MI depends on the vessels involved. Occlusion of the circumflex branch of the left coronary artery causes a lateral wall infarction; occlusion of the anterior descending branch of the left coronary artery, an anterior wall infarction.
True posterior or inferior wall infarctions generally result from occlusion of the right coronary artery or one of its branches. Right ventricular infarctions can also result from right coronary artery occlusion, can accompany inferior infarctions, and may cause right-sided heart failure. With a transmural MI, tissue damage extends through all myocardial layers; with a subendocardial MI, only in the innermost and possibly the middle layers.
Signs and symptoms
The cardinal symptom of an MI is persistent, crushing substernal pain that may radiate to the left arm, jaw, neck, or shoulder blades. Such pain is typically described as heavy, squeezing, or crushing and may persist for 12 hours or more. However, in some MI patients—particularly older adults or diabetics—pain may not occur at all; in others, it may be mild and confused with indigestion.
Gender Influence: MI in womenUntil menopause, women have a lower risk of myocardial infarction (MI) than men because estrogen helps keep the low-density lipoprotein levels down and high-density lipoprotein levels high. It may also help relax the coronary arteries and decrease levels of fibrinogen. After menopause, estrogen levels plummet, resulting in a rise in myocardial problems.
Women also experience atypical signs and symptoms of MI, which may go unnoticed. These include:
burning sensation or discomfort in the upper abdomen
difficulty breathing
nausea and vomiting
weakness or fatigue
profuse sweating
light-headedness and fainting.
Physicians also may not recognize these signs and symptoms as cardiac related and may delay prompt diagnosis and treatment.
In patients with coronary artery disease, angina of increasing frequency, severity, or duration (especially if not provoked by exertion, a heavy meal, or cold and wind) may signal impending infarction.
Other features
Other signs and symptoms include a feeling of impending doom, fatigue, nausea, vomiting, and shortness of breath. Some patients may have no symptoms. The patient may experience catecholamine responses, such as coolness in the extremities, perspiration, anxiety, and restlessness. Fever is unusual at the onset of an MI, but a
low-grade fever may develop during the next few days. Blood pressure varies; hypotension or hypertension may be present.
low-grade fever may develop during the next few days. Blood pressure varies; hypotension or hypertension may be present.
Complications
The most common post-MI complications include recurrent or persistent chest pain, arrhythmias, left ventricular failure (resulting in heart failure or acute pulmonary edema), and cardiogenic shock. Unusual but potentially lethal complications that may develop soon after infarction include thromboembolism; papillary muscle dysfunction or rupture, causing mitral insufficiency; rupture of the ventricular septum, causing ventricular septal defect; rupture of the myocardium; and ventricular aneurysm.
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