Electrocardiogram -Electrical axis and Axis deviation

Electrocardiogram and axis deviation: Mean QRS axis is the magnitude and direction of a mean cardiac dipole or vector Factors affecting mean cardiac vector are the position of heart, properties of the conduction system, electrical property of ventricular myocardium and muscle mass of each ventricle

electrocardiogram

The term mean QRS axis describes the general direction in the frontal plane toward which the qrs complex is predominantly pointed Einthoven triangle can easily be converted to a triaxial lead diagram by having an axis of three standard limb leads 3 augmented limb leads also form a triaxial lead system

Triaxial lead system limb leads


These two triaxial lead system can be combined to produce hexaxial lead diagram Normal mean cardiac vector ranges between -30 to +110 degree

Hexaxial lead system

Different methods of the axis calculation are used. Quadrant method, Three lead analysis, Isoelectric lead method.Quadrant method we are taking two leads for reference lead I and aVF.In both leads, we have to analyse the morphology of QRS whether it is positive negative or isoelectric.

Positive qrs complex

Negative and isoelectric complex


Both are positive axis is normal, Lead I positive and avf negative left axis deviation both are negative then extreme axis deviation Lead I negative and avf positive then right axis deviation

Left axis deviation

Right axis deviation

In three lead analysis lead I, lead II,avf took as reference. Addition of lead II can help determine pathological left axis deviation from the physiological left axis.


In the isoelectric lead method. We have to find isoelectric lead in ECG. Qrs axis will be plus or minus 90 degrees from the lead in the isoelectric lead method.

Isoelectric lead method


An axis of -30 degree or more negative is left axis deviation and 100 degrees or more positive in electrocardiogram is right axis deviation.


Causes of right axis deviation are right ventricular hypertrophy left posterior hemiblock,wpw syndrome and dextrocardia Causes for left axis deviation are left ventricular hypertrophy, left anterior hemiblock, inferior MI and obstructive airway disease

Ecg axis

left posterior hemiblock


Causes for extreme axis deviation are ventricular rhythms, hyperkalemia and severe right ventricular hypertrophy. The same principles of QRS axis calculation can be applied to the mean electrical axis of the p wave and t wave in the frontal plane.

You can also refer this topic in the link

https://www.youtube.com/channel/UCRrYRylZdS67_kbATQrLQqA


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