A 78-year-old man is admitted for investigation of severe aortic stenosis:

Sinus rhythm

• Left axis deviation
• Left bundle branch block

A commonly asked QUESTION is: “Why in this case of left bundle branch block the QRS  in leads V5 and V6  is negative, instead of showing a broad  R, similar to that we see in lead I?”  

The ANSWER: “There is here left bundle branch block (LBBB) with left axis deviation (LAD). The QRS is negative in lead II (as we expect in LAD). Lead V5 and V6 are located  low in the left chest at an angle similar to that of lead II. So it is not surprising that in LBBB with LAD the QRS  in V5 and V6 is often negative”.