Acute myocardial infarction (AMI) is commonly called a heart attack. It is caused by the rapid development of myocardial necrosis (tissue death of a portion of the heart muscle) resulting from a critical imbalance between the oxygen supply and demand of the myocardium. This usually results from plaque rupture with thrombus formation in a coronary vessel, resulting in an acute reduction of blood supply to a portion of the myocardium.

What Causes a Myocardial Infarction:

The most common cause of AMI is narrowing of the epicardial blood vessels due to atheromatous plaques. Plaque rupture with subsequent exposure of the basement membrane results in platelet aggregation, thrombus formation, fibrin accumulation, hemorrhage into the plaque, and varying degrees of vasospasm. This can result in partial or complete occlusion of the vessel and subsequent myocardial ischemia. Total occlusion of the vessel for more than 4-6 hours results in irreversible myocardial necrosis, but reperfusion within this period can salvage the myocardium and reduce morbidity and mortality.

Other causes of AMI include hypoxia, emboli to coronary arteries, arteritis, coronary anomalies, and the use of cocaine, amphetamines, and ephedrine.

Signs and Symptoms of Myocardial Infarction:

There are various signs and symptoms that may indicate a patient may be suffering from myocardial infarction. These signs and symptoms include:

• Chest pain, usually across the anterior precordium, is described as tightness, pressure, or squeezing
• Pain may radiate to the jaw, neck, arms, back, and epigastrium. The left arm is affected more frequently than the right arm.
• Dyspnea, which may accompany chest pain or occur as an isolated complaint, indicates poor ventricular compliance in the setting of acute ischemia.
• Nausea and/or abdominal pain often are present in infarcts involving the inferior wall.
• Anxiety
• Lightheadedness and syncope
• Cough
• Nausea and vomiting
• Diaphoresis
• Wheezing
• Elderly patients and those with diabetes may have particularly subtle presentations and may complain of fatigue, syncope, or weakness.

Diagnosing a Myocardial Infarction:

Upon physical examination:

• Patients with ongoing symptoms might be noted to lie quietly in bed and appear pale and diaphoretic
• Hypertension may precipitate AMI, or it may reflect elevated catecholamines due to anxiety, pain, or exogenous sympathomimetics
• Hypotension indicates ventricular dysfunction due to ischemia. It usually indicates a large infarct and may be observed with a right ventricular infarct.
• Acute valvular dysfunction may be present
• Congestive heart failure (CHF) may occur with neck vein distention, third heart sound (S3), rales on pulmonary examination
• New or worsening mitral regurgitant murmur may be noted
• A fourth heart sound is a common finding in patients with poor ventricular compliance that is due to a preexisting heart disease or hypertension
• Dysrhythmias may be present
• With heart block or right ventricular failure, cannon jugular venous a waves may be noted

Diagnostic Procedures:

When a patient presents with symptoms that could be the result of a myocardial infarction, a physician should immediately order a number of diagnostic procedures to rule out AMI. Any delay in the diagnosis of AMI could result in the death of the patient. Appropriate diagnostic procedures include laboratory studies such as:

• Creatine kinase - MB (CK-MB)
• Myoglobin
• Troponin I
• Complete blood count
  for evidence of leukocytosis, anemia, elevated erythrocyte sedimentation rate (ESR) levels, and elevated serum lactase dehydrogenase (LDH) levels

• Chest x-ray
  A Chest X-ray may provide clues to an alternative or complicating diagnosis (eg, aortic dissection, pneumothorax). The X-ray also reveals complications of AMI, particularly pulmonary edema, and CHF.
• Echocardiography
  Use 2-dimensional and M-mode echocardiography when evaluating wall motion abnormalities and overall ventricular function. This also can identify complications of AMI (eg, valvular insufficiency, ventricular dysfunction, pericardial effusion).
• Technetium-99m sestamibi scan
  Technetium-99m is a radioisotope that is taken up by the myocardium in proportion to the blood flow and is redistributed minimally after injection. This allows for time delay between injection and imaging. It has potential use in identifying infarct in patients with atypical presentations or uninterpretable ECGs. Normal scan findings are associated with an extremely low risk of subsequent cardiac events.
• Thallium scanning
  Thallium accumulates in the viable myocardium.

• Electrocardiogram - Approximately one half of patients have diagnostic changes on their initial ECG.

It should also be kept in mind that patients experiencing AMI may have complications such as tachyarrhythmia, bradyarrhythmia, cardiogenic shock, and valvular insufficiency.

Treatment for a Myocardial Infarction

Once a patient has been diagnosed as suffering from AMI, the patient should receive immediate treatment. Treatment may include:

• All AMI patients should be placed on telemetry
• Two large-bore IVs should be inserted
• Pulse oximetry should be performed, and appropriate supplemental oxygen should be given (maintain oxygen saturation >90 percent)
• The Chest X-Ray should be carefully reviewed to identify possible contraindications to thrombolysis (e.g., aortic dissection)
• The emergency physician should decide whether to administer a thrombolytic agent
• Pharmacologic intervention is likely to include the immediate administration of aspirin and beta-blockade for rate control and decrease of myocardial oxygen demand if not contraindicated
• Additional intervention may include morphine sulphate, anxiolytic, heparin, platelet aggregation (IIb/IIIa receptor) inhibitor, ACE inhibitor
• Antiarrhythmic agent
• Angiography may be performed prior to procedures to re-establish coronary perfusion.
• Percutaneous transluminal coronary angioplasty (generally used selectively for patients failing to respond to thrombolytics)
• Intra-aortic balloon counter pulsation
• PTCA/stenting
• Coronary artery bypass graft (CABG)

Once a patient has been stabilized, additional treatment may consist of prescription of beta-blockers, nitrates, heparin, lidocaine, angiotensin-converting enzyme (ACE) inhibitors, salicylates, thrombolytics, nitroglycerin, and calcium channel blockers, as indicated.

Prognosis for Patients with Myocardial Infarction

Although the prognosis for patients with myocardial infarction depends on a number of factors, the timing and nature of intervention, the success of the intervention (ie, infarct size), and the post-MI management are critical. A delay in diagnosis and treatment, as well as any inappropriate or counterindicated treatment, can result in the death of the patient.

Legal Options

If someone you love has died because a doctor or other health care professional failed to diagnose a Myocardial Infarction (or heart attack) and failed to provide appropriate treatment, you should immediately contact a competent attorney. The attorney will work with you to determine whteher there may a medical malpractice claim resulting from the failure to diagnose or provide appropriate treatment.