The anatomic substrate of complete left bundle branch block.

SUMMARY The conduction systems of eight cases diagnosed clinically as having complete left bundle branch block (LBBB) were serially sectioned. Left axis deviation was present in six and normal axis in two. In all cases there was evidence of ischemia of the myocardium and left bundle branch (LBB) in various parts of the coronary circulation. In all cases, the LBB showed pathologic change at its junction point with the bundle of His, with disruption, complete or incomplete, in six, and with recent and old lesions in two. There was no difference in lesions of the LBB between cases with and without left axis deviation. There is thus complete correlation between the electrocardiographic abnormality LBBB and lesions of the LBB in these cases. The pathogenesis of the LBB lesions in these cases is probably both ischemic and mechanical. Left bundle branch block Pathology Left bundle branch THE ANATOMIC BASIS for the electrocardio-graphic abnormality complete left bundle branch block (LBBB) is today in dispute. According to one group of investigators`9 the anatomic base lies in lesions of the LBB. According to another group,"03 it is doubtful that lesions of the LBB are the basis of complete LBBB, and that other factors have to be sought such as lesions of the nerves or of the myocar-dium itself. We therefore studied the pathology of the conduction system and the entire heart in eight cases which were diagnosed electrocardiographically as having complete LBBB. Our findings lend credence to the view that most cases of LBBB have an anatomic basis in lesions of the LBB. Materials and Methods The electrocardiographic criteria for the diagnosis of complete LBBB were those of the New York State Heart Association.'4 They are as follows: 1) QRS duration of 0.12 sec or greater; 2) presence of a broad monophasic R wave in lead V6; 3) ST depression and T-wave inversion in V6; and 4) absence of Q waves in V6. Pathologically, the coronary arteries were opened by dis-section in the fresh heart. The heart was then opened and examined in a manner previously described,"5 the chambers were packed with cotton, and the heart fixed in 10% for-malin (4% formaldehyde). Histologic examination was then carried out as follows:"5 the sinoatrial (SA) and atrioventricular (A-V) nodes and their approaches and the beginning of the penetrating portion of the bundle were serially sectioned and every twentieth section was retained. The remainder of the penetrating …