I. RIGHT BUNDLE BRANCH BLOCK
The right bundle branch is the continuation of the penetrating AV bundle and runs as a single discrete bundle beneath the endocardium of the ventricular septum to the base of the anterior papillary muscle. The bundle then runs in the moderator band to form a rich anastomos¬ing network of conducting fibers throughout the right ventricle. The subepicardial location and discrete nature of the bundle branch of the rim of the right ventricular outflow makes it vulnerable to trauma from catheters. Because of its discrete nature, the bundle is easily damaged by several diseases including focal hypoplasia that causes congenital right bundle branch block, anteroseptal myo-cardial infarction that commonly affects the ventricular septum, and right ventricular hypertrophy associated with diffuse subendocardial fibrosis.
The electrical bundles that take the electrical impulses to the right ventricle are damaged or do not conduct the impulse; the electrical impulses fail to reach the right ventricle. Complete right bundle branch block occurs when there is a complete interruption of conduction to the right ventricle through the right bundle branch. Diagnosis is made only from the ECG. Figure 2 shows the electrocardiographic genesis of the QRS complex in right bundle branch block (RBBB). Figures 3A, and B show a normal ECG compared with one that depicts the features of RBBB. Note that the QRS complex is wide and can have a duration of greater than 120 ms, whereas in a normal tracing the QRS duration is 80–110 ms. This happens because it takes more time for the electrical current to be conducted from the AV node through the left bundle then for the right ventricle to receive the current.