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K 305
27 June 03
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Contractile Dysfunction
Reversible
•stunning
•hibernation
Irreversible
•necrosis
•apoptosis
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Contractile Dysfunction
This cell damage produces:
• hypocontractility
• enhance the likelihood of arrhythmias
• both of which can be lethal
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Etiology of Ischemia - Reperfusion Injury
•osmotic overload
•number of particles in cytosol as lactate
accumulates and ATP is broken down
•immune response
•neutrophils and complement system
•pH paradox
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Etiology of Ischemia - Reperfusion Injury
•pH paradox
•  pHi which increases:
•Na+-H+ activity
•[Na+]I
•Na+-Ca2+ exchange reverse activity
•[Ca2+]i overload
•contractile dysfunction
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Regulation of Intracellular H+
H+ extrusion (acidosis)
NHE-1
•pH paradox
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EKG changes with ischemia/ MI
Subendocardium
•results in ST segment depression
•injury current at rest causes baseline elevation
•during plateau causes ST segment depression
•observe a J point at the point between the QRS
complex and the ST segment and this point represents
zero current in the heart as all parts of the ventricles are
depolarized
•ST segment depression is usually due to imbalance
between supply and demand and will reverse when
exercise is stopped during a stress test
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EKG changes with ischemia/ MI
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EKG changes with ischemia/ MI
Subepicardium or transmural
•immediately results in heightened T waves
•may be followed by T wave inversion
• T wave inversion problems with directionality of
repolarization
•ST segment elevation occurs due to injury current during
plateau phase of the action potential which is moving
towards epicardium
•deep (dirty, pathological) Q waves reflect scarring
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EKG changes with ischemia/ MI
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Plasma markers of MI
24-72 hours after MI - increases in:
•CK
•LDH
•TnI
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Radionuclide Imaging of Heart
Technetium-99m-MIBI
•MIBI - 2-methoxy isobutyl isonitrile
•MIBI travels via CBF becomes trapped within healthy,
active muscle cells in the heart
•radioactivity monitored with a gamma camera
•during an MI, some muscle cells will not trap the MIBI
•also occurs with CAD except the lack of MIBI in some
of the muscle cells is due to inadequate CBF
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Cardiac Ischemia
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Ischemic Preconditioning
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