Electrocardiogram Tutorial

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1. What does an electrocardiogram measure and what do its component waveforms represent?
2. What do each of the following intervals represent, and what is their normal range in seconds?
   1. PR interval
   2. QRS duration
   3. QT and QTc intervals
3. Where are the electrodes placed on the body for a 12-lead ECG?
4. What is the difference between bipolar and unipolar leads?
5. Where is the location of the positive electrode in each of the following limb leads: I, II, III, aV_R, aV_L, and aV_F?
6. What is the axial reference system and what is the axis (in degrees) for each of the bipolar and unipolar limb leads?
7. What are the rules for determining the direction of a vector of depolarization and repolarization relative to a given ECG lead?
8. Describe, in terms of vectors, how the QRS complex is generated and why the QRS appears differently when viewed by different leads.
9. What is the normal mean electrical axis for the heart?  What is a left and right axis deviation?
10. How can the mean electrical axis be approximated by examining the relative amplitudes of limb leads?

Revised 11/03/06