Question

What is the mean QRS Axis and degrees for the following?

1. Lead I deflection is mostly negative, AVF is mostly positive; biphasic lead is Lead II

2. Lead I deflection is mostly negative, AVF is mostly negative; biphasic lead is AVL

3. Lead I deflection is mostly positive, AVF is mostly positive; biphasic lead is Lead III

Answer 1

Mean QRS axis represents the major vector of ventricular activation, which is the overall direction of electrical activity. Thus it provides direction of electrical activity when the ventricles depolarise.

1)Lead -1 negative; AVF positive—then the axis is rightward(right axis deviation); + 90 to +180 degrees

2)Lead -1 negative; AVF negative—then the axis is “indeterminate” sometimes as “Northwestern axis”. This is uncommon and usually from ventricular rhythms can also be from lead misplacement ; congenital heart disease.It is between +/-180 and -90 degrees.

3)Lead -1 positive;AVF positive- it mainly indicates normal axis;. And the degree is between-30 to +90