Difficulty: Medium

Average Score: 53%

Electrocardiogram
The rhythmic sounds of "beep... beep... beep..." signify the measurement of the heart muscle's strength. This rhythmic signal varies from person to person and is recorded as an electrocardiogram (ECG). Within the body, a complex array of systemic neural responses generates electric currents that can be detected on the skin's surface. When a person is connected to an amplifier, these impulses are captured by an electrocardiograph. Most of the information gathered pertains to the heart, as it emits electric currents in waves. This "wave of excitation" propagates through the heart wall and is associated with electrical changes. The process occurs in three distinct phases. First, the "wave of excitation," accompanied by an electrical change, lasts for about 1 to 2 seconds following the contraction of the cardiac muscle. These electrical impulses are rhythmically discharged from the sinoatrial (SA) node, which acts as the heart's natural pacemaker, signaling the atrium to contract. The peak of the ECG reading is attributed to the atrioventricular (AV) node, which triggers the excitation of the ventricles. Finally, as the ventricles relax, any changes in the wave pattern can alert trained medical personnel to potential abnormalities within the heart.

Which statement is not listed as a detail within the passage?

Rationale

Changes in the ECG are typically used for diagnosis of abnormal cardiac rhythm.

The passage provides details about how an electrocardiogram (ECG) records electrical impulses from the heart, emphasizing the process of excitation and the roles of the SA and AV nodes. However, it does not explicitly mention the diagnostic use of ECG changes for abnormal cardiac rhythms.

A (Changes in the ECG are typically used for diagnosis of abnormal cardiac rhythm.) CORRECT

While ECGs are indeed used diagnostically to identify abnormal rhythms, this specific use is not discussed in the passage. The passage focuses on the process of recording the heart's electrical activity and the role of the SA and AV nodes.

B (The signal has a characteristic record called the electrocardiogram.) YOUR ANSWER

This statement aligns with the extract, which mentions that the heart's electrical signals are recorded as an electrocardiogram, or ECG.

C (The "wave of excitation" starts at the SA node.) YOUR ANSWER

The passage describes the SA node as the heart's natural pacemaker, initiating the "wave of excitation" that signals the atria to contract.

D (The "wave of excitation" spreads through the heart wall and is accompanied by electric changes.) YOUR ANSWER

This detail is covered in the passage, which explains how the "wave of excitation" propagates through the heart wall, involving electrical changes.

Conclusion

The passage primarily discusses the recording of heart electrical activity via an ECG and the roles of the SA and AV nodes in generating this activity. While the passage provides information on how these impulses are recorded and processed, it does not mention the diagnostic application of ECG changes for abnormal cardiac rhythms, making choice A the detail not listed in the passage.

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