Heart Axis; Qtc Parameter - Saadat DENA 1210 User Manual

Chapter 5: ECG analysis and measurement

Heart Axis

The cardiac vector (Heart axis) is the average sum of the electrical forces inside the heart, or
in other words, the angle of the result of the vector of the heart's electrical activity.
The electric vector can be calculated for P, QRS and T waves.
Among cardiac angles, the QRS axis has the most clinical use and is easily calculated. Leads
I, II and III or aVF, aVL and aVR leads can be used to calculate the QRS axis. Each of these
leads shows the electrical activity of the heart in a specific direction. The normal cardiac vector
is in the range of -30 to +90 degrees. The following figure shows the angles corresponding to
each lead.
Figure 5-2 Heart angles related to different leads

QTc parameter

The QT Interval is from the beginning of the QRS to the end of the T wave, which indicates
the duration of ventricular depolarization and repolarization.
Since QT is affected by heart rate, it needs to be corrected and normalized to the heart rate
(normalizing QT means eliminating its dependence on HR). For example, increasing HR
reduces QT, and this dependence needs to be removed to make a diagnostic comparison with
the normal range.
In order to normalize the QT parameter, the following equations are used:
���� 60
������ = ���� = [������]
and
√ ���� ����
41