In left bundle branch block lead V1 shows a deep S-wave and in V6 a broad and clumsy R-wave is noted ( Figure 2, panel B). In lead V6 a broad and deep S wave is noted. Right bundle branch block ( Figure 2, panel A) is characterized by a second R wave (denoted R’) in V1, which gives lead V1 an rSR’ complex. ECG changes in right bundle branch block (RBBB) and left bundle branch block (LBBB) (B): ECG features of left bundle branch block (LBBB). (A): ECG features of right bundle branch block (RBBB).
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This results in characteristic ECG changes depicted in Figure 2.įigure 2. The ventricles whose bundle branch is defect will be depolarized from impulses spreading from the opposite ventricle. Similarly, block in the right bundle branch causes right bundle branch block (RBBB). Overview of bundle branch blocks and fascicular blocks Bundle branch blocks (right and left bundle branch block)Īnatomical or functional block in the left bundle branch causes left bundle branch block (LBBB). Altered electrical axis – Changes in the depolarization sequence may also alter the electrical vectors and thus the electrical axis.In each of these blocks, the QRS morphology will have a characteristic appearance which makes it fairly easy to diagnose them. Altered QRS morphology – Because the normal sequence of depolarization is altered in bundle branch blocks and fascicular blocks, the QRS morphology will also be altered.Similarly, block in the right bundle branch causes right bundle branch block, in which the right ventricle will be depolarized by impulses spreading from the left ventricle. Those impulses will spread through the right ventricle partly or entirely outside of the conduction system which will be slow and therefore cause wide QRS complex.
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The consequence of left bundle branch block is that the left ventricle will be depolarized by impulses spreading from the right ventricle.
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A network of Purkinje fibers sprouts out from the bundle branches an 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 branch 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 intranventricular conduction delay and intranventricular 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. In this chapter we will discuss 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 (contraction).
![ivcd rhythm strip ivcd rhythm strip](https://www.ecgguru.com/sites/default/files/styles/scale_650px_width/public/RBLAH104.jpg)
Intraventricular conduction delay (defect): constellations of bundle branch blocks and fascicular blocks (hemiblocks)