Myocardial Infarction

Posted by e-Medical PPT Thursday, July 14, 2011
Myocardial Infarction if the rapid development of myocardial necrosis by a critical imbalance between oxygen supply and demand to the myocardium.Acute coronary syndromes include
ST-elevation MI (STEMI)
Non ST-elevation MI ( NSTEMI)
Unstable Angina
Cardiac markers in circulation indicates myocardial infarction and help categorize MI and is a useful adjunct to diagnosis.

In the US, 1.3 million cases of nonfatal MI were reported in 2006
Incidence of 600 per 100,000 people
Increase in the proportion of NSTEMI compared to STEMI
Approximately 500,000 to 700,000 deaths are caused by heart disease annually in the United States

Mechanisms of Myocardial damage
The severity of an MI is dependent of three factors
The level of the occlusion in the coronary
The length of time of the occlusion
The presence or absence of collateral circulation

Cardiac Biomarkers
Cardiac biomarkers are protein molecules released into the blood stream from damaged heart muscle
Since ECG can be inconclusive , biomarkers are frequently used to evaluate for myocardial injury
These biomarkers have a characteristic rise and fall pattern

Troponin T and I
These isoforms are very specific for cardiac injury
Preferred markers for detecting myocardial cell injury
Rise 2-6 hours after injury
Peak in 12-16 hours
Stay elevated for 5-14 days

Creatinine Kinase ( CK-MB)
Creatinine Kinase is found in heart muscle (MB), skeletal muscle (MM), and brain (BB)
Increased in over 90% of myocardial infraction
However, it can be increased in muscle trauma, physical exertion, post-op, convulsions, and other conditions
Time sequence after myocardial infarction
Begins to rise 4-6 hours
Peaks 24 hours
returns to normal in 2 days
MB2 released from heart muscle and converted to MB1.
A level of MB2 >or = 1 and a ratio of MB2/MB1 > 1.5 indicates myocardial injury

Leukocytosis may be observed within several hours after myocardial injury and returns returns to levels within the reference range within one week.

Use 2-dimentional and M mode echocardiography when evaluating overall ventricular function and wall motion abnormalities
Echocardiography can also identify complications of MI ( eg. Valvular or pericardial effusion, VSD)...

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