From review of 2,000 electrocardiographic charts, nine were selected in which a hemiblock contralateral to a previous infarction appeared. Coexistence of left anterior hemiblock (LAH) with inferior infarction results in initial r wave in inferior leads, masking ECG signs of infarction. The same phenomenon was also found in cases of left posterior hemiblock (LPH) with anterolateral infarction, where an initial r wave appeared in aVL and L I. Appearance of an R wave in place of a previous pathologic Q wave cannot be assumed as evidence of improvement; on the contrary this change occurs with additional damage that produces conduction defect. The diagnostic value of the variations of the initial 0.02 sec vector is emphasized. Extreme axis deviation may be secondary to infarction or hemiblock; hence the diagnosis of hemiblock should be based also upon the orientation of the first vector and the intrinsicoid deflection time.
