Slight middle slurring in V1-V2 without bundle branch block. An electrocardiographic and follow-up study

A slight middle slurring in V1 and/or V2 with rS morphology (R less than S) in these leads, without right or left bundle branch block is a nearly ignored electrocardiographic finding. The purpose of this work is to provide a prospective and electrocardiographic analysis of this finding. We followed 200 subjects with middle slurring in V1 and/or V2, in the absence of bundle branch block (study group), (age: 41.5 +/- 19 years, follow-up period: 5.7 +/- 2.5 years) and 200 subjects with rS morphology in V1-V2 without the middle slurring (control group), (age: 39.8 +/- 20 years, follow-up period: 5.2 +/- 2 years). The age, sex, prevalence of organic heart disease, QRS duration and follow-up period did not show significant differences between the two group. In the study group there was a higher prevalence of vertical axis (P less than 0.001), of S1S2S3 morphology (P less than 0.001) and of terminal r wave in a VR (P less than 0.05) compared to control group. During the follow-up period, a right bundle branch block appeared in 19 subjects of study group (incomplete in 15 and complete in 4) and in 2 (complete) of control group (P less than 0.001). A left bundle branch block appeared only in one patient of study group and in one of control group. We conclude that the isolated slight middle slurring in V1-V2 expresses an initial involvement of the right bundle branch system and increases the likelihood of appearance of right bundle branch block.