What is left axis deviation?

Left axis deviation (LAD) is an abnormality commonly seen on an electrocardiogram (EKG), a graph of heart activity. When a normal axis falls within a range of -30° to +90° in the right quadrants, a deviation to the left axis would fall anywhere from -30° to -90° in the upper right quadrant of the graph. In general, LAD itself is not problematic unless it is greatly shunted, or is accompanied by other heart problems.

There are many different causes for a left axis deviation. For example, it could be what is called a normal variant, since it shows up only on an EKG without any other indication of heart disease. However, any axis deviation from the normal range is called an ECG abnormality, and further clinical testing is usually recommended when this type of pattern is displayed.

Different types of heart disease can also cause LAD, and some types are more serious than others. A left anterior fascicular block, also known as a left anterior hemiblock, can cause the deviation, but is generally not considered serious in the absence of other ECG irregularities. Additionally, it is known to appear in about 14% of all otherwise normal EKGs taken from patients with no known heart problems.

An inferior myocardial infarction, or heart attack, is a more serious cause of this deviation. However, this tends to be accompanied by other EKG irregularities, as well as physical symptoms of chest pain or loss of consciousness. An abnormal left anterior hemiblock has been found in approximately 4% of myocardial infarctions and has a left axis deviation of between -45° and -60°.

Chronic obstructive pulmonary disease (COPD) and emphysema are two lung diseases that can also cause this problem. Breathing difficulties experienced by those with any of these medical conditions can cause the lungs to chronically inflate and shift the heart to the right. The change skews the EKG reading more toward the left axis than it normally would be. This is sometimes also called mechanical deflection.

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