Introduction to CV Pharmacology - Orlando Health

CV Pharmacology
Measurement of the QTI in stable sinus rhythm
The QTI is measured from the beginning of depolarization of the QRS complex to the end of the
T wave representing repolarization. The QTI may be short, normal, or prolonged (>.44).
Although a short QTI may suggest hypercalcemia, it is often difficult clinically to distinguish
between a normal or short QTI. The literature suggests that healthcare providers should not be as
concerned with QT shortening as with prolongation. (Grauer, 1998). The recommended lead for
measurement is lead II.
Note: If a U wave is present, it is not to be included in the measurement. The possible problem
of distinguishing the T wave from a U wave can be minimized by measuring the QTI in lead II.
Example of QTI measurement (with permission Grauer, 1998)
QTI ends here
where the T-wave
returns to baseline.
Another method to determine if a QTI is prolonged in sinus rhythms (< 100 beats
per minute) is to observe the R-R interval. The QTI is probably prolonged if it
exceeds more than half of the R-R interval.
Example of evaluating R-R interval. (with permission Grauer, 1998)
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