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Kinesiology 3337A/B Midterm: FIt appraisal - ECG notes

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Kinesiology 3337A/B
Glen Belfry

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ECG tracings **what you see on paper is the relation between the vector that is being depolarized by the heart and the axis of the ECG lead (which is generated by the unit/machine)  Left shoulder to right shoulder - both leads in same direction = biggest depolarization wave (QRST section) - as it moves away from parallel (oblique 45 degrees) = ½ the size (smaller depolarization wave) - both leads are perpendicular = NO deflection at all (no tracing present) - leads parallel in opp. direction = large amplitude in the negative direction - as it moves away from parallel in the opp. direction = smaller amplitude in negative direction  Different amplitude waves will be reflected by the different leads  therefore this enables you to look through the heart at different angles to see if the electrical activity in that area has been compromised  More tissue that is being depolarized – the greater the deflection it will be - Therefore, since atrial walls are thinner = smaller depolarization waves; ventricle walls are thicker = greater depolarization waves How does this happen? AT REST  Electrodes at rest are completely polarized  Since both recording electrodes are surrounded by positive charges, no voltage difference = 0 mV and no line PARTIALLY DEPOLARIZED  Positive charges inside the cell and negative outside causes depolarization and this spreads from left to right  Right electrode surrounded by positive charges – ECG reports a positive direction  The amplitude of depolarization is proportional to the mass of myocardium undergoing depolarization COMPLETELY DEPOLARIZED  Depolarization is complete = both electrodes surrounded by negative charges  No voltage difference between electrodes = ECG recordings 0 mV (isoelectric potential) PARTIALLY REPOLARIZED  Repolarization moves form right to left (opposite direction of depolarization) o Reason why they are both complexes are positive (if it moves from left to right – it would be negative)  ECG shows upward (positive) deflection = right hand electrode is surrounded by positive charges COMPLETELY REPOLARIZED  Muscle cells are now completely repolarized (resting state) = ECG records isoelectric line  Myocardial cells are now ready to be depolarized again Limb leads  Goes through the periphery from right (still being depolarized to pump blood to lungs) to left (larger wall thickness – systemic circulation  Even through vector moves to left – still affected by tissues depolarized on the right side of heart  LEAD 1  will not be at a max amplitude wave  LEAD 2  parallel – will have largest amplitude of the SAME event  LEAD 3  angle – still positive – same direction – amplitude will be smaller *DRAW BACK: movement of electrical activity going to by majority of the heart doesn’t go through the middle – just superior or adjacent– getting a general look at the electrical activity occurring Augmented limb leads (Avr, Avl, Avf)  Machine will take exact same cardiac event and switch the polarity (2 negatives going to 1 positive) now vector being generated goes right through the heart instead of a general look Precordial leads  Makes all the leads negative – precordial electrodes on chest are all positive  V leads are all positive – current flow is coming medial – current generated come together in the chest -becomes the negative – not the individual point on the shoulder and hip, its where they all meet in the chest  NEGATIVE EPICENTER  Positive V-leads are interacting with negative V-V6 coming form same epicenter – enables you to look at electrical activity i
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