Dr.S.Venkatesan MD

In one of my classes , this ECG  was presented .  Controversy  erupted.It was about the  basics .

What is the QRS axis  of this ECG  ?

Not surprisingly there were  handful of answers .

1. North west Axis
2. Indeterminate QRS
3. +150
4. +180
5. 0 degrees
6. Extreme Right axis

Which is correct ? My guess  is ,  it should be  closer  to + 180 .  Lead 2 is equiphasic and perpendicular lead is negative limb of AVL ie + 150 .If you  plot Lead 1 and  AVF in graph and calculate  we get + 135 . (In the strict sense , we are not  supposed to take one standard lead and an augmented lead for plotting ). Finally, the strongest argument was ,  since  AVR shows  only positive forces  it  would make  north west axis more likely .

Causes of North west  QRS axis

1. Denova North west axis
2. Extreme Left becoming NWA*
3. Extreme Right  becoming NWA

*Left becoming NWA is much more common than other types.

Chamber enlargement alone is not sufficient to shift the axis to NW corridor. There must be anatomical distortion of  his bundle and it’s branches to shift the axis dramatically .This usually occur in complex congenital heart disease. In acquired heart disease the  an apical VT is probably  an important cause for NWA.

One word about indeterminate qrs axis .

By the way , Indeterminate QRS axis  is not synonymous with north west axis. This term should ideally be used  if qrs complex is equiphasic  in all limb leads , when  qrs  axis  can not be truly determined .This situation commonly occurs when we encounter very very low voltage qrs  as in cardiac tamponade and severe hypothyroidism , constrictive pericardits, etc

If  the QRS is in north west  corrodor , How  to differentiate ,  whether it came from  extreme left axis  or  right axis ?

I am yet to find a correct answer for this.

1. Pre-cardial pattern will help.
2. A  q in V5/V6 would suggest  extreme left axis.
3. May be we have to look the initial qrs vector in AVR lead for more clues

Traditionally , we talk about net qrs axis . We should realise net qrs axis is a combination of initial and late vectors .It can be dramatically different in different leads . QRS axis is  a two dimensional representation of three or more  (omni) dimensional electrical forces .That is the source for confusion. So,  do not unduly worry about the complexity .Blame it on the limitations of surface ECG !

Expecting some comments .