Cardiac Arrhythmia - Blocks3-Third Degree (Complete) Atrioventricular Block

Third Degree (Complete) Atrioventricular Block

Complete heart block occurs when atrial contraction is normal but no beats are conducted to the ventricles. The atrial rhythm is independent of the ventricular rhythm, unless an accessory pathway that conducts antegrade is present. It is most easily distinguished from high grade atrioventricular nodal block when the atrial and ventricular rhythms are regular but have different rates.
Because of weak coupling between the chambers by the auronomic nervous system, these rates can be very close to each other (a phenomenon known as ventriculo phasic sinus arrhythmia).

  
case1: 
         The ventricular contractions are caused by autonomic escape rhythms and thus will have a constant RR interval. When the conduction starts within or close to, the atrioventricular node a narrow complex escape rhythm ensues. 

                                                                           Conduction

           Electrocardiogram - Narrow QRS Complex





case2:
          If a broad QRS complex escape rhythm is visible, then the conduction is of ventricular origin and thus may be considered as a ventricular escape. The closer the origin to the atrioventricular node, the faster the rate.
Because the rhythms of the atria and the ventricles are unrelated, complete heart block is said to exhibit atrioventricular disassociation.

                                                                            Conduction

         Electrocardiogram - Narrow QRS Complex