Myocardial Infarction

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 MI than premenopausal women, although incidence is rising among females, especially those who smoke and take oral contraceptives.

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 heart failure. .In transmural MI, tissue damage extends through all myocardial layers; in subendocardial MI, only in the innermost and possibly the middle layers.

Signs and symptoms

The following are the most common symptoms of a heart attack. However, each individual may experience symptoms differently. Symptoms may include:

• severe pressure, fullness, squeezing, pain and/or discomfort in the center of the chest that lasts for more than a few minutes
• pain or discomfort that spreads to the shoulders, neck, arms, or jaw
• chest pain that increases in intensity
• chest pain that is not relieved by rest or by taking cardiac prescription medication
  
• chest pain that occurs with any/all of the following (additional) symptoms: sweating, cool, clammy skin, and/or paleness
• shortness of breath
• nausea or vomiting
• dizziness or fainting
• unexplained weakness or fatigue
• rapid or irregular pulse

Although chest pain is the key warning sign of a heart attack, it may be confused with indigestion, pleurisy, pneumonia, or other disorders.

The symptoms of a heart attack may resemble other medical conditions or problems. Always consult your physician for a diagnosis.

Diagnosis

Persistent chest pain, ST-segment changes on the electrocardiogram (ECG), and elevated levels of total creatine kinase (CK) and the CK-MB isoenzyme over a 72-hour period usually confirm MI. Auscultation may reveal diminished heart sounds, gallops and, in papillary dysfunction, the apical systolic murmur of mitral insufficiency over the mitral valve area.

When clinical features are equivocal, assume that the patient has had an MI until tests rule it out. Diagnostic test results include the following:

• serial 12-lead ECG: ECG abnormalities may be absent or inconclusive during the first few hours following an MI. When present, characteristic abnormalities include serial ST-segment depression in subendocardial MI and ST­segment elevation in transmural MI.
• serial serum enzyme levels: CK levels are elevated specifically, CK-MB or troponin levels.
• echocardiography: may show ventricular wall motion abnormalities in patients with a transmural MI.

Scans using I.V. technetium 99 can identify acutely damaged muscle by picking up radioactive nucleotide, which appears as a "hot spot" on the film. They lire useful in localizing a recent MI.

Treatment

The goals of treatment are to relieve chest pain, to stabilize heart rhythm, to reduce cardiac workload, to revascularize the coronary artery, and to preserve myocardial tissue. Arrhythmias, the predominant problem during the first 48 hours after the infarction, may require antiarrhythmics, possibly a pacemaker and, rarely, cardioversion.

To preserve myocardial tissue, thrombolytic therapy should be started I.V. within 3 hours after the onset of symptoms (unless contraindications exist). Thrombolytic therapy includes either streptokinase, alteplase, recombinant tissue plasminogen activator (t-PA), retivase, or urokinase.

Percutaneous transluminal coronary angioplasty (PTCA) may be another option. If PTCA is performed soon after the onset of symptoms, the thrombolytic agent may be administered directly into the coronary artery.

Prevention

To prevent a heart attack:

• Control your blood pressure.
• Control total cholesterol levels. To help with cholesterol control, your doctor may prescribe a medication of the statins group (atorvastatin, simvastatin).
• Stop smoking if you smoke.
• Eat a low fat diet rich in fruits and vegetables and low in animal fat.
• Control diabetes .
• Lose weight if you are overweight.
• Exercise daily or several times a week by walking and other exercises to improve heart fitness. (Consult your health care provider first.)

If you have one or more risk factors for heart disease, talk to your doctor about possibly taking aspirin to help prevent a heart attack.

After a heart attack, follow-up care is important to reduce the risk of having a second heart attack. Often, a cardiac rehabilitation program is recommended to help you gradually return to a "normal" lifestyle. Follow the exercise, diet, and medication regimen prescribed by your doctor.