Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
Publisher: Cengage Learning,
ISBN: 9781337794909

Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
Publisher: Cengage Learning,
ISBN: 9781337794909


Chapter 13, Problem 9RQ
Textbook Problem

The normal duration of the ST segment is

A. 0.12 second or less

B. 0.15 second or less

C. 0.20 second or less

D. 0.50 second or less

Expert Solution
Summary Introduction


The electrocardiogram (ECG) consists of intervals, waveforms, segments, and baselines. It is recorded on a graph having small and large squares. The large square corresponds to a time duration of 0.20 seconds and each large square contains five small squares corresponding to 0.04 seconds. The standard ECG contains the P wave, PR interval, QRS complex, T wave, QT interval, U wave, and ST segments. The waveform begins and ends with the baseline and two or more waveforms combine to form a complex. The flat line on the graph or isoelectric line is known as a segment. The ST segment is one such segment.

Explanation of Solution

Justification/ Explanation for the correct answer:

Option (a) is, ‘0.12 seconds or less.’ The ST segment represents the time between the depolarization and repolarization of the ventricles. This segment begins where the QRS complex ends and this segment ends at the start of the T wave. This segment lasts for 0.12 seconds or less. Hence, option (a) is correct.

The explanation for the incorrect answers:

Option (b) is, ‘0.15 seconds or less.’ This ST segment normally lasts for a duration of 0.12 seconds or less and an increase in the duration of the ST segments denotes an abnormality in the functioning of the heart. The ST segment is generally elevated or depressed in the case of myocardial injury and other factors...

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