The Conduction System of the Swine Heart (5)Left Bundle Branch
This passes between the left infundibular and ventricular muscle (Fig 2, bottom, and 6). During its passage, its cells are smaller in diameter than ventricular myocardial cells. It again shows an increase in collagenous, connective, and elastic tissue as compared with the ventricular myocardial cells. It thus reaches the endocardium of the left ventricle where it remains a discrete large bundle. Its parenchymal cells become larger in diameter than ventricular working cells, resembling typical Purldnje cells. This bundle then breaks up into anterior and posterior radiations, which in turn break up into smaller fasciculi supplying the left ventricle. Throughout its course, the left bundle branch is full of nerve fibers, but no nerve cells. buy ventolin inhalers

Right Bundle Branch
Most of the right bundle branch (Fig 2, top) is intramyocardial. In the beginning, it lies adjacent to the annulus of the tricuspid valve. The cells in this part have the same or a smaller diameter than the working myocardial cells. Here, again, there is a marked increase in collagenous connective tissue and elastic tissue as compared with the ventricular myocardium. Gradually, as it progresses downward, the cells equal in diameter the ventricular myocardial cells. As they reach the endocardium of the right ventricle, they have a larger diameter than the working cells and may be called Purldnje cells. There is a distinct increase in collagenous connective and elastic tissue throughout the right bundle branch as compared with the working myocardium (Fig 7). Numerous nerve fibers accompany the right bundle branch throughout its course (Fig 7).


Figure 6 (at left). Left bundle branch passing between conal and ventricular muscle (Gomori trichrome stain X 45). C = conal muscle; V = ventricular muscle. Arrows point to left bundle branch.


Figure 7 (helow). Right bundle branch, (a, left), Weigert-Van Gieson stain X 150, (b, right), Holmes silver stain X450. V = ventricular muscle; RBB = right bundle branch. Arrows point to nerve fibers.