GRAPHIC DISPLAY OF ELECTROCARDIOGRAM
a. Heart Electrical Forces. During the cardiac cycle (one contraction of the
heart plus the relaxation period that follows), electrical changes take place in the heart.
These changes can be visualized and recorded.
(1) Detection of electrical forces in the heart. Electrical forces in the heart
can be detected on the body's surface. Therefore, electrodes attached to the patient's
skin can detect electrical forces in the heart.
(2) Recording of electrical forces in the heart. The recording of the electrical
changes during the cardiac cycle is called an electrocardiogram (ECG or EKG). The
instrument used to record these changes is an electrocardiograph.
b. Electrocardiogram Graph Paper and Machines. Electrocardiogram graph
paper and the speed of the EKG machines are standard and uniform. Lines on the
graph paper are horizontal and vertical with four light lines between two heavy lines.
The horizontal lines indicate voltage. The electrical voltage of the heart impulse is
measured in millivolts and determined by the magnitude of deflection (the power of a
(1) Determination of electrical impulse strength. Compare the height of a
wave spike to the horizontal lines to determine the strength of the electrical impulse.
(2) Vertical lines. Vertical lines indicate the speed of the electrical current
traveling within the heart. The distance in time between two heavy vertical lines is 0.20
seconds and between two light vertical lines or across one small square is 0.04
(3) Heavy lines. Heavy lines are necessary to determine rates, rules, and
normal values. Light lines are composed of five small columns between two heavy
Squares. There are 25 squares in each large square.
(5) Standard rate of EKG paper. The standard rate of EKG paper travels
past the stylus at a rate of millimeters per second.
(6) Graph paper markings. The markings on the graph paper can be
examined and compared to normal markings to give the reader an idea of the electrical
activity of the patient's heart. See figure 2-4 for an example of standard EKG graph