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H‐V Intervals in Left Bundle‐Branch Block: Clinical and Electrocardiographic Correlations

H-V interval in left bundle-branch block (LBBB) reflects conduction time in the His bundle and right bundle branch. H-V intervals were measured in 57 patients with LBBB, allowing definition of three groups of patients. Group A consisted of 14 patients with normal H-V (less than 50 msec), group B consisted of 21 patients with intermediate H-V (50-60 msec), and group C consisted of 22 patients with prolonged H-V (greater than 60 msec).Arteriosclerotic heart disease (ASHD) was most frequent in group A (P < 0.02), while hypertension was most frequent in group C (P < 0.15). Mean P-R interval ± SEM was 0.172 ± 0.013 sec in group A, 0.185 ± 0.007 sec in group B, and 0.225 ± 0.014 sec in group C (P < 0.05). Mean QRS duration was 0.138 ± 0.004 sec in group A, 0.144 ± 0.004 sec in group B, and 0.157 ± 0.003 sec in group C (P < 0.01). Mean frontal axis was −8° ± 12° in group A, −16° ± 12° in group B, and −28° ± 8° in group C (NS).The frequent association of LBBB, normal H-V, and ASHD suggested the presence of isolated ischemic disease of the left bundle branch. In contrast, the frequent association of LBBB, prolonged H-V, and absence of ASHD was suggestive of sclerodegenerative bilateral bundle-branch disease. In a patient with LBBB, the occurrence of both first-degree A-V block and a QRS duration of 0.16 sec or greater strongly suggested the likelihood of H-V prolongation.