This 73-year-old man with a long history of coronary artery disease and severe left ventricular dysfunction is in the cardiac clinic for a follow-up assessment:

• Sinus bradycardia, 53/min
• Left atrial enlargement
• Left axis deviation
• Left bundle branch block

When we review this ECG, a frequently asked question is: “Why is the QRS complex negative in V5 and V6 in this patient with LBBB? Shouldn’t be expect a broad R without S waves?”

The Answer:
The ECG of patients with LBBB most frequently shows a broad R in the left chest leads. In this case, however, there is left axis deviation and the mean QRS vector is directed to the left and superiorly, giving an rS pattern in lead II. Lead V5 and V6 are in left lower area of the chest and often show a pattern similar to lead II.