Myocardial infarction

Acute myocardial infarction (AMI or MI), commonly known as a heart attack, is a serious, sudden heart condition usually characterized by varying degrees of chest pain or discomfort, weakness, sweating, nausea, vomiting, and arrhythmias, sometimes causing loss of consciousness. It occurs when a part of the heart muscle is injured, and this part may die because of sudden total interruption of blood flow to the area. It is often a life-threatening medical emergency which demands both immediate attention and activation of the emergency medical services.

Diagnosis

Myocardial infarctions vary greatly in severity. Classical cases of myocardial infarction are often identified by ambulance staff, emergency room doctors and cardiac specialist nurse practitioners quickly. Yet many myocardial infarctions, tending to be smaller, are not recognized by victims, never receive medical attention and result in either sudden death or progressive heart weakness. For a more complete diagnosis, the medical history, combined with electrocardiogram results and blood tests for heart muscle cell damage, are vital. Myocardial perfusion tests (see stress tests) and echocardiograms can also be helpful.

Related Topics:
Heart weakness. - Electrocardiogram - Blood test - Stress tests

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Electrocardiogram

Electrocardiogram (ECG/EKG) findings suggestive of MI are elevations of the ST segment and changes in the T wave. After a myocardial infarction, changes can often be seen on the ECG called Q waves, representing scarred heart tissue.

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The ST segment elevation distinguishes between STEMI and NSTEMI (myocardial infarction without ST elevation). The latter is diagnosed when cardiac enzymes are elevated.

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Myocardial markers

Cardiac enzymes are proteins from cardiac tissue found in the blood. Until the 1980s, the enzymes SGOT and LDH were used to assess cardiac injury. Then it was found that disproportional elevation of the MB subtype of the enzyme creatine phosphokinase (CPK) was very specific for myocardial injury. Current guidelines are generally in favor of troponin isoenzymes I or T, which are thought to rise before permanent injury develops. A positive troponin in the setting of chest pain may accurately predict a high likelihood of a myocardial infarction in the near future.

Related Topics:
1980s - SGOT - LDH - Creatine phosphokinase - Troponin

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The diagnosis of myocardial infarction used to require that all three components (history, ECG, and enzymes) were positive for MI. Currently the cardiac enzymes have become so reliable that enzyme elevations alone are considered reliable measures of cardiac injury, with ECG serving to determine where in the heart the damage has occurred, and history serving to screen patients for further enzyme and ECG testing.

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In difficult cases or in situations where intervention to restore blood flow is appropriate, an angiogram can be done (see below for an image). Using a catheter inserted into an artery (usually the femoral artery), obstructed or narrowed vessels can be identified, and angioplasty applied as a therapeutic measure (see below). Angiography requires extensive skill, especially in emergency settings, and may not always be available out of hours. It is commonly performed by cardiologists. There is a very small risk of plaque and vessel rupture on ballon inflation; should this occur, then emergency open-chest cardiac surgery may be required. Patients commonly experience bruising at the catheter insertion point in the groin and occasionally a hematoma. Dissection (tearing) of the blood vessel is rare but usually managed with a local thrombotic injection.

Related Topics:
Angiogram - Femoral artery - Angioplasty - Cardiologists - Bruising - Hematoma - Dissection - Thrombotic

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