IHD Patho 2012_Student Version (1)

Atrioventricular av node his bundle left right atrial

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atrioventricular (AV) node His Bundle left / right atrial bundle branches Purkinje fibers P-wave: Atrial depolarization QRS complex: Ventricular depolarization T-wave: Ventricular repolarization
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12-lead ECG Essential diagnostic tool in patients who present with ACS Provides immediate and invaluable data vial for expeditious diagnosis, prognosis, and management 1. Identifies the presence of myocardial ischemia, injury, or infarction 2. Location of the infarction 3. Site of the occlusion in the coronary artery involved Photo adopted from: http://www.ivline.info/2010/05/quick-guide-to-ecg.html
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Electrocardiographic Changes STE MI NSTE MI / UA ST-segment depression T-wave inversion No ECG changes ST-segment elevation A 12-lead ECG should be obtained and interpreted within 10 minutes of patient presenting to emergency department The lead(s) in which ECG changes occur gives idea of which coronary artery is occluded Q waves usually develop at some point following a STE MI
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Electrocardiographic  Findings Resting ECG normal in 50% May have various ST-segment or T wave changes ST-segment elevation Suggest acute infarction ST-segment depression Suggest acute ischemia T-wave inversion Suggest acute ischemia Variant angina ST-segment elevation Silent ischemia ST-segment depression or elevation Significant ischemia = ≥ 2 mm ST-segment depression
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Electrocardiographic Changes Later forms a Q-wave
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ECG Adopted from: http://www.merck.com/mmpe/sec07/ch070/ch070e.html Q waves are NOT normal! Sign of old MI
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ST-Segment Elevation ST-segment elevation is the EARLIEST sign of sign of myocardial infarction; occurs ≤ hours of the onset of symptoms MOST STE Mis are “Q-wave MIs” Q-waves may appear ≤ 1 to 2 hours of onset of symptoms, often 12 hours, and occasionally up to 24 hours
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ECG Changes in STE MI Photo adopted from: http://ecg-plymouth.co.uk/resources.html ST normalizes Inverted T wave Q wave deeper T wave inversion ST & T normal Q wave persists
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NSTE MI / UA Findings Photo adopted from: http://www.med.umich.edu/lrc/ecgoftheweek/cases/case11/summary02.html T-wave Inversions ST-Segment Depression OR Most NSTE MIs are NOT Q-wave MIs Weeks later ST-segments and T-waves normalize; no Q waves
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Cardiac Biomarkers Creatine kinase MB Troponins Myoglobin Released into bloodstream when myocardial necrosis occurs Differentiates between UA and NSTEMI / STEMI UA has negative cardiac biomarkers Photo adopted from: http://www.metrohealth.org/body.cfm?id=1484
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Creatine Kinase Intracellular enzyme found within muscle cells Isoforms = CK-MM, CK-BB, CK-MB Elevated within 2-4 hours Peak = Within 24 hours Return to baseline = 2-3 days Less sensitive and less specific than troponins
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CK-MB Single measurement not adequate to exclude diagnosis of MI Need at least 2 CK-MB values greater than MI decision limit (set by hospital laboratory) to make clinical diagnosis of STE MI or NSTE MI Baseline, 6-12 hr, and 12-24 hr Can also be elevated in patients with skeletal muscle injury or renal dysfunction
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