1. Measurement of PR and QT intervals and the heart rate. A
Measurement of PR and QT intervals and the heart rate. A.Leads I, II, and III. PR interval is measured with the three-channel device. The exact PR interval measurement is the distance from the earliest onset of the P wave in any lead (in this case, lead III) to the earliest onset of the QRS complex in any lead (in this case, also in lead III). Measurement of QT interval: The QT interval should be measured from the onset of the Q wave to the latest end of the T wave. The corrected QT (QTc; QT in relation to heart rate) is obtained with a ruler (C), which gives us the result when the end of two R-R cycles coincides with the QTc value obtained on a ruler; in this case, the QTc is 390 ms. The value of QT in this ECG, 400 ms, is equal to a QTc of 390 ms plus 10 ms. It is considered a normal value that does not exceed, as in this case, ± 10% to 15% of the QTc shown on the ruler. Measurement of the heart rate: The same ruler gives the heart rate, in this case approximately 60 beats/min. B. This panel shows (1) the normal QT interval; (2) an example of the long QT interval (LQT3; see Fig. 15–80B); (3) the short QT interval of asymptomatic people; and (4) the QT interval of symptomatic short QT syndrome (the distance between point J and T peak is short—100 ms; see Fig. 15–80A).
Source: Chapter 15. Surface Electrocardiography, Hurst's The Heart, 13e
Citation: Fuster V, Walsh RA, Harrington RA. Hurst's The Heart, 13e; 2011 Available at: Accessed: September 22, 2017
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