Page 1731 - Saunders Comprehensive Review For NCLEX-RN

FIG. 52-1 Coronary arterial system.

Box 52-1

Basics of Electrocardiography

▪ An electrocardiogram (ECG) reflects the electrical activity of cardiac cells and
records electrical activity at a speed of 25 mm/second.
▪ An electrocardiographic strip consists of horizontal lines representing seconds
and vertical lines representing voltage.
▪ Each small square represents 0.04 second.
▪ Each large square represents 0.20 second.
▪ The P wave represents atrial depolarization.
▪ The PR interval represents the time it takes an impulse to travel from the atria
through the atrioventricular node, bundle of His, and bundle branches to the
Purkinje fibers.
▪ Normal PR interval duration ranges from 0.12 to 0.2 second.
▪ The PR interval is measured from the beginning of the P wave to the end of the
PR segment.
▪ The QRS complex represents ventricular depolarization.

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