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Learn ECG: How to Determine the Heart Axis

The electrical heart axis is routinely and easily obtained during analysis of an electrocardiogram (ECG). A significant deviation from the normal range suggests the presence of an underlying cardiac or noncardiac problem and indicates the need for further investigation. Apart from coronary anatomy, understanding the principles of axis determination is a good entry point to learn ECG interpretation.

The electrical axis of the heart is the mean direction of the cardiac impulse during ventricular depolarization. The QRS complex, which represents ventricular depolarization, is used for the determination of the electrical heart axis. The term, electrical heart axis, usually refers to the electrical axis in the frontal plane as measured by the limb leads.

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In determining the electrical heart axis in the frontal plane, analysis of two or more limb leads is required.

Vector analysis for the determination of the electrical heart axis:

In determining the electrical heart axis on the ECG curve using vector analysis, ventricular depolarization is represented as a mean depolarization vector with an arrow pointing to a specific direction. The length of the vector represents the magnitude of the potential created by the difference in the charges between the activated (or depolarized) cardiac cells and the resting cardiac cells while the direction of the arrow represents the mean direction of the depolarization vectors with reference to the frontal leads (or the limb leads). By definition, ventricular depolarization propagates from a negatively charged area towards a positively charged area. Thus, the mean depolarization vector points to the positively charged area.

Determining the heart axis is an effective means for beginners to learn ECG concepts faster and more easily. For an in-depth review of ECG interpretation as well as other topics related to critical care, please visit our distance learning courses at ExpertCollege.

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