In electrocardiography, left axis deviation (LAD) is a condition wherein the mean electrical axis of ventricular contraction of the heart lies in a frontal plane direction between −30° and −90°. This is reflected by a QRS complex positive in lead I and negative in leads aVF and II. Cause.
https://en.wikipedia.org/wiki/Left_axis_deviation
Quick Answer. Left axis deviation is a condition in which the electrical axis of the heart's ventricular depolarization is abnormally positioned between negative 30 and negative 90, which suggests an underlying anatomical or physiological condition is affecting the electrical conduction system of the heart.
https://www.reference.com/health/left-axis-deviation-85e9d1bbf85224a6
Left axis deviation may be caused by a heart attack. An EKG is often used to continuously monitor the heart rate and rhythm of a critically ill patient in order to catch abnormalities quickly. A left axis deviation is a common abnormality spotted on an electrocardiogram. COPD is a possible cause of left axis deviation. Left axis deviation may be caused by heart disease. During an electrocardiogram, electrodes are placed on the skin to monitor electrical impulses inside the heart.
http://www.wisegeek.com/what-is-left-axis-deviation.htm
Left axis deviation: What that means is the doctor who was caring for you has not been very pleasant or helpful. Two things to do: 1: Please have your doctor explain all of the information to you. There is absolutely no reason why that did not happen already.
https://www.healthtap.com/topics/left-axis-deviation-health-risks
Right axis deviation. The electric axis of the heart is the net direction in which the wave of depolarisation travels. It is measured using an electrocardiogram (ECG). Normally, this begins at the atrioventricular node (AV node); from here the wave of depolarisation travels down to the apex of the heart.
https://en.wikipedia.org/wiki/Right_axis_deviation
The diagram below illustrates the relationship between QRS axis and the frontal leads of the ECG. Normal Axis = QRS axis between -30° and +90°. Left Axis Deviation = QRS axis less than -30°. Right Axis Deviation = QRS axis greater than +90°.
https://lifeinthefastlane.com/ecg-library/basics/axis/
Both terms relate to both the anatomy & electrical activity within the ventricles, both depolarization (left axis deviation) and then repolarization (T waves). Depolarization is delayed toward right vs. left side of ventricles. Repolarization pattern not normal; many reasons. ...Read more.
https://www.healthtap.com/topics/left-axis-deviation-health-risks
A positive QRS in Lead I puts the axis in roughly the same direction as lead I. A positive QRS in Lead aVF similarly aligns the axis with lead aVF. Combining both coloured areas – the quadrant of overlap determines the axis. So If Lead I and II are both positive, the axis is between 0° and +90° (i.e. normal axis).
https://lifeinthefastlane.com/ecg-library/basics/axis/
Fascicular block. Blockage of the left posterior fascicle would lead to activation of the anterior portion of the left ventricle followed by activation of the rest of the ventricle in a superior to inferior direction and directed towards the right. This would lead to right axis deviation findings on an ECG. Bifascicular block is a combination of right bundle branch block and either left anterior fascicular block or left posterior fascicular block. Conduction to the ventricle would therefore be via the remaining fascicle.
https://en.wikipedia.org/wiki/Right_axis_deviation
The diagram below illustrates the relationship between QRS axis and the frontal leads of the ECG. 1  Normal Axis = QRS axis between -30° and +90°. 2  Left Axis Deviation = QRS axis less than -30°. 3  Right Axis Deviation = QRS axis greater than +90°. 4  Extreme Axis Deviation = QRS axis between -90° and 180° (AKA “Northwest Axis”).
https://lifeinthefastlane.com/ecg-library/basics/axis/
what causes left axis deviation on ecg
Left axis deviation on ECG may be caused by a heart attack. On an electrocardiogram, left axis deviation may be caused by a heart attack.