Ekg labCardiac electrophysiology

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Ekg labCardiac electrophysiology

  1. 1. Conduction System of the Heart and Electrocardiography
  2. 2. The Cardiac Cycle <ul><li>Heart at rest </li></ul><ul><ul><li>Blood flows from large veins into atria </li></ul></ul><ul><ul><li>Passive flow from atria into ventricles </li></ul></ul><ul><li>Atria (R & L) contract simultaneously </li></ul><ul><ul><li>Blood forced into ventricles </li></ul></ul><ul><li>Ventricles (R & L) contract simultaneously </li></ul><ul><ul><li>Atrioventricular valves close  “lubb” sound </li></ul></ul><ul><ul><li>Blood forced into large arteries </li></ul></ul><ul><li>Ventricles relax </li></ul><ul><ul><li>Semilunar valves close  “dub” sound </li></ul></ul><ul><li>Heart at rest </li></ul>
  3. 3. Depolarization and Impulse Conduction <ul><li>Heart is autorhythmic </li></ul><ul><li>Depolarization begins in sinoatrial (SA) node </li></ul><ul><li>Spread through atrial myocardium </li></ul><ul><li>Delay in atrioventricular (AV) node </li></ul>
  4. 4. Depolarization and Impulse Conduction <ul><li>Spread from atrioventricular (AV) node </li></ul><ul><ul><li>AV bundle </li></ul></ul><ul><ul><li>Bundle branches </li></ul></ul><ul><ul><li>Purkinje fibers </li></ul></ul>
  5. 5. Depolarization and Impulse Conduction <ul><li>Depolarization in SA node precedes depolarization in atria, AV node, ventricles </li></ul>
  6. 6. Electrocardiogram <ul><li>Method developed by Wilhelm Einthoven </li></ul><ul><ul><li>Dutch “Elektrokardiogram” (EKG) </li></ul></ul><ul><ul><li>Now usually “ECG.” </li></ul></ul><ul><li>Records electrical events (movements of ions) in heart. </li></ul><ul><ul><li>Variations in electrical potential radiate from heart; detectable at wrists, ankles. </li></ul></ul>
  7. 7. Electrocardiogram <ul><li>P wave </li></ul><ul><ul><li>Depolarization of atria </li></ul></ul><ul><ul><li>Followed by contraction </li></ul></ul><ul><li>QRS complex </li></ul><ul><ul><li>3 waves (Q, R, & S) </li></ul></ul><ul><ul><li>Depolarization of ventricles </li></ul></ul><ul><ul><li>Followed by contraction </li></ul></ul><ul><li>T wave </li></ul><ul><ul><li>Repolarization of ventricles </li></ul></ul>
  8. 8. Electrocardiogram <ul><li>P-Q interval </li></ul><ul><ul><li>Time atria depolarize & remain depolarized </li></ul></ul><ul><li>Q-T interval </li></ul><ul><ul><li>Time ventricles depolarize & remain depolarized </li></ul></ul>
  9. 9. Electrocardiogram <ul><li>Einthoven’s triangle </li></ul><ul><ul><li>Three standard limb leads </li></ul></ul><ul><ul><li>Voltage differences between corners of triangle </li></ul></ul><ul><ul><li>We will use “Lead II” </li></ul></ul><ul><ul><ul><li>Right shoulder to left leg </li></ul></ul></ul>
  10. 10. Electrocardiogram <ul><li>Intervals show timing of cardiac cycle </li></ul><ul><ul><li>P-P = one cardiac cycle </li></ul></ul><ul><ul><li>P-Q = time for atrial depolarization </li></ul></ul><ul><ul><li>Q-T = time for ventricular depolarization </li></ul></ul><ul><ul><li>T-P = time for relaxation </li></ul></ul>
  11. 11. Electrocardiogram <ul><li>Intervals show timing of cardiac cycle </li></ul><ul><li>How does timing change with activity? </li></ul>
  12. 12. Electrocardiography <ul><li>Null hypothesis </li></ul><ul><li>H 0 : Intervals (P-Q, Q-T, T-P) change in proportion to one another from rest to exercise, i.e. ratios (exercise/rest) show NO change. </li></ul>

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