Conduction abnormalities in the His-Purkinje tissue
The ventricles are activated by the left and right bundles and the Purkinje system. The rapid conduction velocity of these specialized myocytes leads to almost simultaneous activation of the entire myocardium, which in turn leads to a narrow QRS complex recorded by the ECG (usually less than 0.10 s). However, abnormalities of the bundles will lead to sequential activation of the ventricles that in turn will cause a wide QRS complex. The left bundle is composed of two major divisions: anterior and posterior. Abnormal conduction in one of these divisions or fascicles of the left bundle will not necessarily lead to a wide QRS complex but will cause characteristic QRS patterns on the ECG. The recognition of different types of conduction abnormalities in the bundle branches and fascicles will be the subject of this chapter.