15 ischemia injury & infarct2

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  • Insufficient blood supply to the myocardium can result in myocardial ischemia, injury or infarction, or all three. Atherosclerosis of the larger coronary arteries is the most common anatomic condition to diminish coronary blood flow. The branches of coronary arteries arising from the aortic root are distributed on the epicardial surface of the heart. These in turn provide intramural branches that supply the cardiac muscle. Myocardial ischemia generally appears first and is more extensive in the sub-endocardial region since these deeper myocardial layers are farthest from the blood supply, with greater intramural tension and need for oxygen.
  • The term infarction describes necrosis or death of myocardial cells. Atherosclerotic heart disease is the most common underlying cause of myocardial infarction. The left ventricle is the predominant site for infarction; however, right ventricular infarction occasionally coexists with infarction of the inferior wall of the left ventricle. The appearance of pathological Q waves is the most characteristic ECG finding of transmural myocardial infarction of the left ventricle. A pathological Q wave is defined as an initial downward deflection of a duration of 40 msec or more in any lead except III and aVR. The Q wave appears when the infarcted muscle is electrically inert and the loss of forces normally generated by the infarcted area leaves unbalanced forces of variable magnitude in the opposite direction from the remote region, for example, an opposite wall. These forces can be represented by a vector directed away from the site of infarction and seen as a negative wave (Q wave) by electrodes overlying the infarcted region.During acute myocardial infarction, the central area of necrosis is generally surrounded by an area of injury, which in turn is surrounded by an area of ischemia. Thus, various stages of myocardial damage can coexist. The distinction between ischemia and necrosis is whether the phenomenon is reversible. Transient myocardial ischemia that produces T wave, and sometimes ST segment abnormalities, can be reversible without producing permanent damage and is not accompanied by serum enzyme elevation. Two types of myocardial infarction can be observed electrocardiographically:Q wave infarction, which is diagnosed by the presence of pathological Q waves and is also called transmural infarction. However, transmural infarction is not always present; hence, the term Q-wave infarction may be preferable for ECG description , Non-Q wave infarction, which is diagnosed in the presence of ST depression and T wave abnormalities.
  • The term infarction describes necrosis or death of myocardial cells. Atherosclerotic heart disease is the most common underlying cause of myocardial infarction. The left ventricle is the predominant site for infarction; however, right ventricular infarction occasionally coexists with infarction of the inferior wall of the left ventricle. The appearance of pathological Q waves is the most characteristic ECG finding of transmural myocardial infarction of the left ventricle. A pathological Q wave is defined as an initial downward deflection of a duration of 40 msec or more in any lead except III and aVR. The Q wave appears when the infarcted muscle is electrically inert and the loss of forces normally generated by the infarcted area leaves unbalanced forces of variable magnitude in the opposite direction from the remote region, for example, an opposite wall. These forces can be represented by a vector directed away from the site of infarction and seen as a negative wave (Q wave) by electrodes overlying the infarcted region.During acute myocardial infarction, the central area of necrosis is generally surrounded by an area of injury, which in turn is surrounded by an area of ischemia. Thus, various stages of myocardial damage can coexist. The distinction between ischemia and necrosis is whether the phenomenon is reversible. Transient myocardial ischemia that produces T wave, and sometimes ST segment abnormalities, can be reversible without producing permanent damage and is not accompanied by serum enzyme elevation. Two types of myocardial infarction can be observed electrocardiographically:Q wave infarction, which is diagnosed by the presence of pathological Q waves and is also called transmural infarction. However, transmural infarction is not always present; hence, the term Q-wave infarction may be preferable for ECG description , Non-Q wave infarction, which is diagnosed in the presence of ST depression and T wave abnormalities.
  • 15 ischemia injury & infarct2

    1. 1. 12-LeadElectrocardiography a comprehensive course ia, Is chem I nju ry, & Inf arct Par t 2) ( Adam Thompson, EMT-P, A.S.
    2. 2. Evolution of MI• Insufficient blood supply to the myocardium. – Ischemia, injury or infarction, or all three.• The branches of coronary arteries arising from the aortic root are distributed on the epicardial surface of the heart.• These in turn provide intramural branches that supply the cardiac muscle.• Myocardial ischemia generally appears first.
    3. 3. Evolution of MIIschemia Injury Infarction Needs O2 Damage from Irreversible lack of O2 damage
    4. 4. Ischemia• Subendocardial ischemia – Ischemia in this area prolongs local recovery time. Since repolarization normally proceeds in an epicardial-to-endocardial direction, delayed recovery in the subendocardial region due to ischemia does not reverse the direction of repolarization but merely lengthens it.
    5. 5. Ischemia• Transmural ischemia – is said to exist when ischemia extends subepicardially. This process has a more visible effect on recovery of subepicardial cells compared with subendocardial cells. Recovery is more delayed in the subepicardial layers, and the subendocardial muscle fibers seem to recover first.
    6. 6. Ischemia• Hyperacute T-Waves – Results from subendocardial ischemia – Symmetrical & tall – Wide with blunt peak (unlike Hyperkalemia) – Present for about first 30 min. of AMI• Inverted T-waves – Results from transmural ischemia
    7. 7. IschemiaAsymmetricalSymmetrical
    8. 8. Ischemia
    9. 9. Ischemia-Mimic Hyperkalemia STE-Mimic Inverted T-WavesPeaked T-Waves
    10. 10. Injury• Injury to the myocardial cells results when the ischemic process is more severe.• In patients with coronary artery disease, ischemia, injury and myocardial infarction of different areas frequently coexist, producing mixed and complex ECG patterns.
    11. 11. Injury• ST-Depression – Subendocardial• ST-Elevation – Subepicardial – Transmural.
    12. 12. Injury
    13. 13. Injury ST-ElevationST-Depression
    14. 14. Injury-MimicHyperkalemia STE-Mimic ST-Elevation
    15. 15. Infarct• The term infarction describes necrosis or death of myocardial cells.• Atherosclerotic heart disease is the most common underlying cause of myocardial infarction.• The left ventricle is the predominant site for infarction; however, right ventricular infarction occasionally coexists with infarction of the inferior wall of the left ventricle.
    16. 16. Infarct• During acute myocardial infarction, the central area of necrosis is generally surrounded by an area of injury, which in turn is surrounded by an area of ischemia.• Various stages of myocardial damage can coexist.• The distinction between ischemia and necrosis is whether the phenomenon is reversible.
    17. 17. Infarct• Pathological Q-waves – Wider than 0.04sec / 40ms (1 small box) – Deeper than 25% the height of R-Wave
    18. 18. Part 2• More up next…

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