A. Electrocardiogram (ECG) [Figure 3-3]
- represents atrial depolarization.
- does not include atrial repolarization, which is "buried" in the QRS complex.
2. PR interval
- is the interval from the beginning of the P wave to the beginning of the Q wave (initial depolarization of the ventricle).
-varies with conduction velocity through the atrioventricular (AV) node. For example, if AV nodal conduction decreases (as in heart block), the PR interval increases.
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