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

l-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 inter-mediate 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 ° + 120 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 asso-ciation of LBBB, prolonged H-V, and absence of ASHD was suggestive of sclero-degenerative 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. Additional Indexing Words: A-V block A-V conduction Bilateral bundle-branch block Hypertensive heart disease P-R interval RECORDING of His bundle electrograms allows definition of the electrocardio-graphically silent H-V interval, from His bundle depolarization to the onset of ventricu