Intraventricular conduction delay

ST-T wave abnormalities secondary to intraventricular conduction disturbances (eg, left or right bundle branch block) look similar to those that occur during ischemia. The ST segments may be depressed or elevated; when there is an ST segment shift present, it is most often in a direction opposite to the polarity of the QRS complex. The T wave also has a polarity opposite to the direction of the QRS complex. Thus, there are typically ST segment depressions and T wave inversions in leads V1 to V3 with a right bundle branch block (RBBB), reflecting repolarization abnormalities of the right ventricular myocardium. Repolarization changes in the left ventricular myocardium due to a left bundle branch block (LBBB) result in downsloping ST depression and T wave inversion in leads V4 or V5 to V6.