<prompt> An 89-year-old man with hypertension, presents for routine follow-up. ECG shows?LBBBRBBBST elevationExtreme axis deviation  <response>: Ans. a LBBB. There is sinus rhythm at a rate slightly slower than 100 beats min. The qRS axis is normal. Ihe PR interval is prolonged to greater than 200 milliseconds consistent with AV conduction delayfirst-degree AV block. The qRS complex is wide greater than 120 milliseconds with a broad S wave in lead VI and a broad, notched R wave in leads I, aVL, and V6 diagnostic of left bundle branch block. I here are ST-segment elevations in leads VI through V3, which are normal in the setting of a left bundle branch block. Similarly, the ST-segment depressions and T-wave inversions in leads V5 through V6, 1, and aVL are normal features of left bundle branch block. In general, the ST segment and T wave should be directed opposite to the major polarity of the QRS complex when left bundle branch block is present.WiLLiaMV1 W QRS patternV6 M QRS patternQRS 0.12sV1-QSV6-rSRLeft bundle branch block characteristics MaRRoWV1 M QRS patternV6 W QRS patternQRS 0.12sV1-rSR dominant R wave V6-delayed SRight bundle branch block characteristics 