Digital recording of lecture
MP3 file requires an MP3 player
Powerpoint Presentation (P3)
(~ 5 Mb)
I. Cardiac Ischemia
A. Contractile Dysfunction
Reversible - stunning and hibernation. The stunned myocardium is in a short term state of hypocontractility. Hibernation is longer term state of hypocontractility and may be cardioprotective.
Irreversible - necrosis and to a lesser degree apoptosis
these states will produce hypocontractility and enhance the likelihood of arrhythmias both of which can be lethal
B. Etiology of Ischemia - Reperfusion Injury
osmotic overload - due to number of particles in cytosol as lactate accumulates and ATP is broken down\
immune response: neutrophils and complement system. Neutrophils may be attracted to the site of injury
pH paradox: ¯ pHi which increases: Na+-H+ activity, [Na+]i , Na+-Ca2+ exchange reverse activity and [Ca2+]i calcium overload: [Ca2+]i causes activation of certain proteases, contracture and mitochondrial uptake ( ¯ ATP production).
C. EKG changes with ischemia/ MI:
endocardial ischemia results in ST segment depression. Injury current at rest causes baseline elevation and 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.
epicardial or transmural ischemia immediately results in heightened T waves and may be followed by T wave inversion. T wave inversion represents 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. This is the acute MI phase.
prolonged ischemia results in necrosis and can be seen as pathological Q waves. Concerns if Q wave is > 30 ms or 25% of the QRS complex. Q waves occur because the necrotic area is electrically silent but acts as a window to let the lead see tissue on the other side of the lumen. From the perspective of the lead at this site the current is in the opposite direction causing a negative deflection. Pathological Q wave persists for the life of the individual after an infarct.
D. Serum changes with MI
24-72 hrs later increases in cardiac specific isoforms of LDH, CK and TnI
E. Radionuclide Imaging of the Heart
F. Ischemic Preconditioning