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Electrocardiogram
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 best summary of the passage?

  • A. Electric currents within the body result from the heart's electrostatic charges. Trained medical staff can identify heart abnormalities.
  • B. Each individual exhibits unique electric currents on the body's surface, which the ECG records and measures.
  • C. The ECG systematically captures the stages of the 'wave of excitation' within the heart, originating from the SA node to the AV node, in three distinct steps.
  • D. The ECG records the body's electric currents, detectable on the body's surface through an amplifier.
Correct Answer: C

Rationale: The passage discusses how the electrocardiogram (ECG) measures the 'wave of excitation' in the heart, detailing the three distinct steps from the SA node to the AV node. Option A is incorrect as it oversimplifies the process and does not focus on the ECG's specific function. Option B is partially correct but lacks the key point about the stages of excitation and the nodes involved. Option D is too general and does not highlight the specific process of the 'wave of excitation' as explained in the passage. Therefore, Option C is the best summary as it accurately reflects the systematic measurement and recording of the 'wave of excitation' within the heart by the ECG.