Third degree AV block (complete heart block) is often an ominous rhythm requiring close monitoring for hemodynamic compromise, progression to ventricular standstill or asystole and other lethal dysrhythmias. Significant characteristics of this rhythm are: 1) lonely P waves - P wave without an accompanied QRS complex and 2) chaotic PR intervals. A narrow QRS denotes a higher junctional block while a wide QRS points more towards a sub-nodal block high in the bundle branches.
In the image can be diagnosed by the presence of solitary P waves, which are not followed by a QRS complex in addition to the slow frequency. In addition, patients present syncope and dizziness.
Treatment consists of pacemaker placement.
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