<P> In junctional rhythm, however, the sinoatrial node does not control the heart's rhythm--this can happen in the case of a block in conduction somewhere along the pathway described above . When this happens, the heart's atrioventricular node takes over as the pacemaker . In the case of a junctional rhythm, the atria will actually still contract before the ventricles; however, this does not happen by the normal pathway of activation and instead is due to a backwards or retrograde conduction (conduction comes from the AV node into and through the atria). </P> <P> Junctional rhythm can be diagnosed by looking at an ECG: it usually presents without a P wave or with an inverted P wave . Retrograde P waves refers to the depolarization from the AV node back towards the SA node . </P>

P waves originating in the middle of the av junction/bundle of his area will be