Acute+MI+Diagnostics

 -**Those w/ACS**: Risk for Acute Myocardial Infarction (AMI) based on presenting characteristics: ECG, serum cardiac markers, timing of presentation.
 * -Acute Coronary Syndrome includes:** acute ischemic heart dz's like NSTEMI, STEMI, unstable angina.

o T-Wave Inversion: T-wave & ST segment à Usually 1st to be involved during myocardial ischemia and injury. à As involved area becomes ischemic, myocardial repolarization is altered, causing changes in T wave (usually T-wave inversion) o ST-segment depression or elevation: ST changes occur w/ischemia that produces myocardial injury. If acute injury is transmural à overall ST vector is shifted in direction of outer epicardium à ST elevation. When injury is confined to subendocardium à overall ST shifts toward inner ventricular layer à ST depression. o Development of abnormal q-wave: Occurs when there is no depolarizing current conduction fr. necrotic tissue à signify transmural infarction or ST-segment elevation AMI. -These changes vary depending on duration of ischemic event (acute vs. evolving), it’s extent (subendocardial vs. transmural) and location (anterior vs. posterior) -Continuous and 12-lead ECG monitoring à Usually Indicated.
 * I. ECG Changes**


 * II. Serum Markers:** As myocardial cells become necrotic, intracellular enzymes & other components diffuse into surrounding interstitium à then into blood. Rate at which the serum markers appear in blood depends on intracellular location, molecular weight, & local blood flow. The following are serum markers:


 * a. Myoglobin**: Oxygen-carrying protein, similar to hemoglobin. Normally present in cardiac & skeletal muscle. Released quickly fr. infracted myocardial tissue à elevated within 1 hr. after myocardial cell death. Peak levels reached w/in 4-8h. B/c it’s present in both cardiac & skeletal muscle à it’s NOT cardiac specific.


 * b. Creatinine kinase**-**MB:** Intracellular enzyme found in muscle cells. CK exceeds normal ranges within 4-8 hrs. of myocardial injury. Declines to normal within 2-3 days. 3 isoenzymes of CK à MB is highly specific to myocardial tissue.


 * c. Troponin I (TnI) & Troonin T (TnT):** Part of troponin complex à which is part of actin filament that regulate calcium-mediated actin-myosin contractile process in striated muscle. à TnI & TnT: present in cardiac muscle à Rise w/in 3h after onset of MI à may remain eeveated for 7-10 days after the event. à Troponin assays à more capable of detecting episodes of MI where cell damage is insufficient to produce a rise in CK-MB level.