Alternative names

Myocardial infarction; MI; Acute MI

Definition

A heart attack (myocardial infarction) occurs when an area of heart muscle dies or is permanently damaged because of an inadequate supply of oxygen to that area.

Causes, incidence, and risk factors

Most heart attacks are caused by a clot that blocks one of the coronary arteries (the blood vessels that bring blood and oxygen to the heart muscle). The clot usually forms in a coronary artery that has been previously narrowed from changes related to atherosclerosis. The atherosclerotic plaque (build up) inside the arterial wall sometimes cracks, and this triggers the formation of a clot, also called a thrombus.

A clot in the coronary artery interrupts the flow of blood and oxygen to the heart muscle, leading to the death of heart cells in that area. The damaged heart muscle loses its ability to contract, and the remaining heart muscle needs to compensate for that weakened area.

Occasionally, sudden overwhelming stress can trigger a heart attack.

The risk factors for coronary artery disease and heart attack include:

• Smoking
• High blood pressure
• Too much fat in your diet
• Poor blood cholesterol levels, especially high LDL ("bad") cholesterol and low HDL ("good") cholesterol
• Diabetes
• Male gender
• Age
• Heredit

Many of the risk factors listed are related to being overweight.

Newer risk factors for coronary artery disease have been identified over the past several years. Heart attacks account for 1 out of every 5 deaths. It is a major cause of sudden death in adults.

Symptoms

Chest pain behind the sternum (breastbone) is a major symptom of heart attack, but in many cases the pain may be subtle or even completely absent (called a "silent heart attack"), especially in the elderly and those with diabetes. Often, the pain radiates from your chest to your arms or shoulder; neck, teeth, or jaw; abdomen or back. Sometimes, the pain is only felt in one these other locations.

The pain typically lasts longer than 20 minutes and is not fully relieved by rest or nitroglycerine, both of which can relieve pain from angina.

The pain can be intense and severe or quite subtle and confusing. It can feel like:

• Squeezing or heavy pressure
• A tight band on the chest
• "An elephant sitting on [your] chest"
• Bad indigestion

Other symptoms you may have either alone or along with chest pain include:

• Shortness of breath
• Cough
• Lightheadedness - dizziness
• Fainting
• Nausea or vomiting
• Sweating, which may be profuse
• Feeling of "impending doom"
• Anxiety

Signs and tests

During a physical examination, the doctor will usually note a rapid pulse. Blood pressure may be normal, high, or low. While listening to the chest with a stethoscope, the doctor may hear crackles in the lungs, a heart murmur, or other abnormal sounds.

The following tests may reveal a heart attack and the extent of heart damage:

• Electrocardiogram (ECG) -- single or repeated over several hours
• Echocardiography
• Coronary angiography
• CT angiography
• Nuclear ventriculography

The following tests may show the by-products of heart damage and factors indicating you have a high risk for heart attack:

• Troponin I and troponin T (proteins involved in muscle contraction)
• CPK and CPK-MB
• Serum myoglobin

Treatment

A heart attack is a medical emergency! Hospitalization is required immediately into the coronary care unit. Continuous ECG monitoring is started immediately, because life-threatening arrhythmias (irregular heart beats) are the leading cause of death in the first few hours of a heart attack.

The goals of treatment are to stop the progression of the heart attack, to reduce the demands on the heart so that it can heal, and to prevent complications.

If the ECG recorded during chest pain shows a change called "ST-segment elevation," angioplasty with stenting or thrombolytic therapy (blood-thinning drugs) are two options to be considered.

Cardiac intervention and other procedures

Emergency coronary angioplasty may be required to open blocked coronary arteries. This procedure may be used instead of thrombolytic therapy, or in cases where thrombolytics should not be used. A device called a stent is often inserted into the artery during angioplasty, to help ensure that the newly opened coronary artery remains open after surgery. Emergency coronary artery bypass surgery (CABG) may be required in some cases.

Recent evidence supports the use of angioplasty and stenting as the first-line therapy to reopen a clogged heart artery if this procedure can be performed in a timely manner in an experienced centre. If this procedure is not available, the use of thrombolytic therapy is warranted.

Blood thinning medications

If angioplasty or stenting are not options, thrombolytic therapy may be started within 12 hours of when chest pain began. This initial clot-dissolving therapy will be administered as an IV infusion of streptokinase or tissue plasminogen activator, and will be followed by an IV infusion of heparin.

Heparin or clexane therapy, designed to prevent the formation of new clots, will last for 48 to 72 hours.

Thrombolytic therapy is not appropriate for people who have had:

• Bleeding inside their head known as an intracranial haemorrhage
• Brain abnormalities such as tumours or blood vessel malformations
• Stroke within the past 3 months (or possibly longer)
• Head injury within the past 3 months

Additionally, thrombolytic therapy is extremely dangerous in those who have had:

• Severe high blood pressure
• A major surgery or major trauma within the past 3 weeks
• Internal bleeding within the past 2-4 weeks
• Peptic ulcer disease

This therapy is also very dangerous in women who are currently pregnant, and in people who use blood thinners such as Warfarin.

Use of thrombolytic therapy can be complicated by significant bleeding. Your doctor can help you find the right therapy.
Medications and fluids will be inserted directly into a vein using an intravenous (IV) line. Various monitoring devices may be necessary. A urinary catheter may be inserted to closely monitor fluid status.

Oxygen is usually given, even if blood oxygen levels are normal. This makes oxygen readily available to the tissues of the body and reduces the workload of the heart.

Pain control medications

Intravenous nitroglycerin or other medicines are given for pain and to reduce the oxygen requirements of the heart. Morphine and similar medicines are potent pain killers that may also be given for a heart attack.

A cornerstone of therapy for a heart attack is antiplatelet medication. Such medication can prevent the collection of platelets at a site of injury in a blood vessel wall -- like a crack in an atherosclerotic plaque. Platelets collecting and accumulating is the initial event that leads to clot formation. One antiplatelet agent widely used is aspirin. Two other important antiplatelet medications includes clopidogrel (Plavix).

Other medications

• Beta-blockers (like metoprolol, atenolol, and propranolol) are used to reduce the workload of the heart and lower blood pressure.
• ACE Inhibitors (accupril) are used to prevent heart failure and lower blood pressure.

Expectations (prognosis)

The expected outcome varies with the amount and location of damaged tissue. The outcome is worse if there is damage to the electrical conduction system (the impulses that guide heart contraction).

Approximately one-third of cases are fatal. If the person is alive 2 hours after an attack, the probable outcome for survival is good, but may include complications.

Uncomplicated cases may recover fully; heart attacks are not necessarily disabling. Usually the person can gradually resume normal activity and lifestyle, including sexual activity.

Complications

• Arrhythmias such as ventricular tachycardia, ventricular fibrillation, heart blocks
• Congestive heart failure
• Cardiogenic shock
• Infarct extension: extension of the amount of affected heart tissue
• Pericarditis (inflammation around the lining of the heart)
• Pulmonary embolism (blood clot in the lungs)
• Complications of treatment (For example, thrombolytic agents increases the risk of bleeding.)

Contact your GP if you are concerned or if you have the above symptoms

Call 111 if:
Crushing chest pain or other symptoms suggestive of heart attack occur.

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 doctor 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.

Update Date: 11/14/2005

Updated by: Steven Kang, MD, Division of Cardiac Pacing and Electrophysiology, Cardiovascular Consultants Medical Group, Oakland, CA. Review provided by VeriMed Healthcare Network.