(Read the passage and answer the following questions)
Beep!…Beep!…Beep! is the audible rhythmic sound made as the strength of the heart muscle is measured. The signal cadence has a characteristic record that varies in every individual. This record is called an electrocardiogram, or ECG.
In the body, an array of systemic neural responses constantly occur, emitting electric currents. The electric currents can be detected on the surface of the body, and if a person is hooked to an amplifier, these impulses are recorded by an electrocardiograph.
Most of the information obtained is about the heart because the heart sends out electric currents in waves. This “wave of excitation” spreads through the heart wall and is accompanied by electric changes. The wave takes place in three distinct steps.
Initially, the “wave of excitation” accompanied by an electric change lasts for approximately 1 to 2 seconds after the contraction of the cardiac muscle. The electric impulses are discharged rhythmically from the sinoatrial (SA) node, the pacemaker of the heart. This spread of excitation over the muscle of the atrium indicates that the atrium has contracted.
Next, the peak of the ECG reading is due to the atrioventricular (AV) node, causing the ventricle to become excited.
Finally, the ventricles relax, and any changes in the wave indicate to trained medical staff any abnormalities within the heart.
What is the author's primary purpose in writing the essay?
A. To persuade the reader to have an ECG
B. To entertain the reader with a heart-warming story
C. To inform the reader how an electrocardiograph reads the electric currents emitted by the heart
D. To analyze the difference in the SA node and the AV node
Which statement is not listed as a detail within the passage?
A. Changes in the ECG are typically used for diagnosis of abnormal cardiac rhythm.
B. The signal has a characteristic record called the electrocardiogram.
C. The “wave of excitation” starts at the SA node.
D. The “wave of excitation” spreads through the heart wall and is accompanied by electric changes.
What is the meaning of the word emitting as it is used in the second paragraph?
What is the main idea of the passage?
A. Electric currents within the body are due to electrostatic charges set off by the heart.
B. The ECG systematically and quickly measures the stages at which the “wave of excitation” occurs within the heart and records them.
C. The “wave of excitation” is detected on the surface of the body and is used to measure the atrial excitation of the heart.
D. The electric currents within the body are in direct relation to the “wave of excitation” measured by the ECG.
What is the best summary of the passage?
A. Electric currents within the body are due to electrostatic charges set off by the heart. Medical staff are trained to recognize any abnormalities within the heart.
B. Every individual has unique electric currents on the surface of the body. The ECG measures and records these electric currents.
C. The ECG systematically and rather quickly measures the stages at which the “wave of excitation” occurs within the heart and records them. This wave has three distinct steps that spread from the SA node to the AV node.
D. The ECG measures the electric currents within the body. These currents are detected on the surface of the body when the body is connected to an amplifier.
What are the three steps of the “wave of excitation”?
A. The discharge from the SA node, the peak ECG, and the excitement of the ventricle.
B. The excitement of the ventricle, the relaxing of the ventricle, and the systemic neural response.
C. The contraction of the atrium, the relaxation of the atrium, and the contraction of the ventricle.
D. The excitation of the atrium, the excitement of the ventricle, and the relaxing of the ventricle.