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Third Degree AV Nodal Block Third Degree AV Block (Example) Third degree AV nodal block (a.k.a. third degree heart block or complete heart block) occurs when NO action potentials conduct through the AV node. This results in the P waves (atrial depolarizations) being completely unrelated to the QRS complexes (ventricular depolarizations). So the P waves occur at one rate and the QRS complexes at another. In this situation where the ventricles NEVER see action potentials originating from the atria, the ventricles compensate by making action potentials of their own. However, the ventricles are unable to create action potentials at a fast rate, so the ventricular rate (QRS complexes) is slow (around 30-40). The atrial rate, indicated by the P waves, however, is faster than the ventricular rate (around 60-100). |
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