The type of ECG changes that occur are as follows: An intraventricular conduction delay may occur whenever any of the main components of the conduction system is dysfunctional.Ĭonduction defects in the bundle branches and/or fascicles cause characteristic ECG changes. Components of the ventricular conduction system and the temporal association between the ECG and impulse transmission through the heart. The current chapters discuss conduction defects located in the bundle branches and in the fascicles.įigure 1. Note that conduction defects in the atrioventricular (AV) node and the bundle of His have been discussed in the previous chapter. Impulse conduction through the Purkinje network is very fast (4 m/s) which enables the vast majority of ventricular myocardium to be depolarized approximately simultaneously.įigure 1 shows the components of the conduction system. A network of Purkinje fibers sprouts out from the bundle branches and fascicles and spread through the ventricular endocardium. Purkinje fibers are branched off from the right bundle branch at the level of the origin of the anterior papillary muscle. The right bundle branch does not give off any Purkinje fibers during its passage through the septum. The interventricular septum obtains Purkinje fibers from the left bundle branch. More precisely this system consists of the bundle of His, the left and right bundle branches and the fascicles of the left bundle branch (Figure 1). The intraventricular conduction system is composed of the His-Purkinje system. Normal and abnormal intraventricular impulse conduction Note that the terms intraventricular conduction delay and intraventricular conduction defect are used interchangeably. These concepts will be discussed in detail in this and the subsequent articles. The primary ECG manifestations of conduction defects are prolonged QRS complexes and altered QRS appearance. This is due to the fact that the left ventricle pumps against greater resistance and any disturbance in ventricular activation will reduce the efficiency of the pumping function. In general, a conduction defect in the left ventricle is more significant, as compared with a defect affecting the right ventricle. The significance of this will depend on the severity of the conduction defect and the affected ventricle. This chapter discusses intraventricular conduction delays (defects), which are caused by functional or anatomical defects in the components of the intraventricular conduction system. Because the conduction system is crucial for rapid and synchronized activation of the ventricles, conduction defects will typically cause abnormal ventricular activation (i.e. Intraventricular conduction delay (defect): constellations of bundle branch blocks and fascicular blocks (hemiblocks)

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