Figure 13-23 When the impulse hits an area of refractoriness in the right bundle branch, the impulse is forced to continue by direct cell-to-cell transmission throughout the rest of the right ventricle.
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We covered aberrancy in Chapter 6, Electrocardiography and Arrhythmia Recognition in some detail, but a few reminders wouldn’t hurt at this point. PACs are usually not associated with any aberrancy of the QRS complexes. The main reason is that most PACs allow ample time for the electrical conduction system in the ventricles to completely repolarize and thus avoid issues with refractoriness. However, occasionally you will get some PACs that come extra early, and these are the ones that cause the problem.
The most common pattern of aberrancy is a right bundle branch block pattern (Figure 13-23). This is because the right bundle branch has the longest refractory period. Once an impulse hits an area of refractoriness, it needs to continue its march through the ventricles by the slow cell-to-cell means of conduction. This slow conduction means that the QRS is wider and, therefore, more aberrant (Figures 13-24 and 13-25).
Figure 13-23 When the impulse hits an area of refractoriness in the right bundle branch, the impulse is forced to continue by direct cell-to-cell transmission throughout the rest of the right ventricle.
© Jones & Bartlett Learning.
Figure 13-24 The right bundle branch block pattern is caused by the slow conduction through the right ventricle.
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Figure 13-25 This rhythm strip shows the typical presentation for a PAC in lead II. The PAC causes the formation of an aberrancy with a right bundle branch block morphology.
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DescriptionLeft bundle branch block pattern is encountered less often, but does occur. It is usually associated with patients who have some structural or ischemic heart disease.