ABSTRACT
This chapter looks at how problems can occur with the subsequent conduction of ventricular rhythms. When there are conduction problems at the atrioventricular (AV) node or bundle of His, conduction of impulses between the atria and ventricles is affected. This can take several forms or ‘degrees’. In first-degree AV block, conduction through the AV node is slower than usual and the PR interval is therefore prolonged. Nonetheless, every P wave is followed by a QRS complex and therefore there are no ‘dropped’ beats. In second-degree AV block, there starts to be an intermittent failure of AV conduction and as a result some P waves are not followed by QRS complexes. In third-degree AV block, there is complete interruption of conduction between atria and ventricles, so that the two are working independently. In left bundle branch block conduction down the left bundle has failed, and so the left ventricle cannot be depolarized in the normal way via its Purkinje fibres.
