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Scientific Proceedings (108). 



ventricular system. As the main deflections in the two sets of 

 electrocardiograms were in opposite directions, it was to be ex- 

 pected that the lesions, if any, in the two instances, would be 

 found on opposite sides of the heart. There has been consider- 

 able theoretical discussion as to which type of electrocardiogram 

 is associated with right-sided and which with left-sided block. 



The first case showed electrocardiographically a main deflection 

 inverted in lead I, upright in leads II and III, a marked widening 

 of the foot-points of the Q.R.S. complex, and only moderate 

 voltage; in addition there was auricular fibrillation. Microscopic 

 examination of serial sections of the A.-V. system, showed that 

 the right bundle branch became attenuated almost immediately 

 after its origin from the main stem, and was surrounded by con- 

 nective tissue. This diminution became more pronounced until 

 at a distance of 7.5 mm. from the bifurcation, scarcely one or two 

 doubtful muscle fibers could be seen. Below this the right 

 branch increased in size again until at 4 cm. below the bifurcation 

 it was of normal dimensions. There was marked fibrous myo- 

 carditis of the septum, involving chiefly the left side, especially 

 the sub-endocardial region. The left branch presented no lesion. 



The second case showed, on two examinations at an interval 

 of six weeks, electrocardiograms in which the main deflection 

 was upright in lead I, inverted in leads II and III, was notched, 

 and its foot-points abnormally separated. Wave P was present 

 throughout. Serial sections showed the A.-V. node, stem and right 

 branch intact. The left bundle branch was imbedded in dense 

 fibrous tissue throughout its course, and at a distance of 3.5 cm. 

 below its origin, its posterior (dorsal) half was replaced by con- 

 nective tissue continuous with an adherent, organized mural 

 thrombus. There was also a thrombus within the apex of the 

 right ventricle, partially adherent to its right lateral wall, but 

 not involving the septum. In addition, there was a general fibrous 

 myocarditis which predominated in the left side of the septum, 

 and an intense thickening of the endocardium on the left side only. 



The direct application of the published electrocardiograms 

 associated with experimental bundle branch lesion in dogs to the 

 interpretation of bundle branch block in man is rendered some- 

 what doubtful by certain anatomical pecularities of the dog's 



