1. ECG

2. ECG stands for Electrocardiography
the record of electrical signal of the heart
Can be used to analyze the mechanical activity of the heart

3. The intrinsic conduction system
Components:
SA node (highest rate of discharge, sets the rate of depolarization for the heart; aka pacemaker)  atria
AV node  atrial contraction (delayed until complete)
AV bundle (Bundle of His)
Right & left bundle branches
Purkinje fibers  ventricular contraction
Repolarization of the SA node is spread throughout the atria while the ventricles depolarize. Then the ventricles repolarize  ventricular diastole

6. Components of the ECG Isoelectric line- a straight line
P wave- atrial depolarization  ~ atrial contraction
QRS complex- ventricular depolarization  ~ ventricular contraction
T wave- ventricular repolarization  ~ ventricular relaxation
Segments- period of time from the end of one wave to the beginning of the next wave ex. ST segment
Intervals- one wave + a segment of the isoelectric line between waves ex. PR interval

7. Isoelectric line & P Wave

8. QRS Complex

9. T wave

10. PR (PQ) Interval

11. ST segment

12. Question?
Is it normal for athletes to have low resting heart beat ~ 50 BPM & left ventricular hypertrophy?
What about same condition seen in sedentary individuals?
YES NO

13. Mean electrical axis
tells us the net direction the depolarization or repolarization is heading (-ve to +ve)
Einthoven’s Triangle: configuration of 3 leads = standard bipolar limb lead
Einthoven’s Law:
Lead I + Lead II = Lead III (QRS)
Q + R + S = net QRS complex

14. Algebra

15. p188
Find the Net QRS amplitude for lead I (0.1mv gradations). Draw a perpendicular line to lead I. (Note +ve or –ve direction)
Find the Net QRS amplitude for lead III. Draw a perpendicular line to lead III. (Note +ve or –ve direction)
Determine the point of intersection of these 2 perpendicular lines.
Draw a new vector from the center point (0,0) to the point of intersection.
Approximate mean electrical axis (5º gradations)

16. Ex. Lead I = +13.5

17. Lead III = +9

18. Mean electrical axis = 58º