A case of non-conducted atrial bigeminy simulating a second-degree atrioventricular block. A holter ECG diagnosis

A 82-years-old man, symptomatic for fatigue and lypothymia, was referred to our centre in order to evaluate the opportunity of a permanent pacemaker insertion. A 12-lead ECG was described as a Mobitz type II second-degree atrioventricular block with 2:1 conduction. This surface ECG revealed some sinus beats with normal AV conduction, everyone followed by a bizarre, non-conducted P' wave, inscripted in the previous T wave. The Holter ECG showed a sinus rhythm with a mean rate of 70 beats/minute: during the night and at 06:39 pm of the following day, ECG strip showed some sinus beats, everyone followed by an atrial non-conducted ectopic beat, characterized by prematurity and abnormal shape (P' wave), that appears as a small deformation on the preceding T wave. At the beginning and the end of the strip we can estimate respectively 9 and 4 sinus beats, that represent the normal rhythm of this patient. So, it is possible to compare the normal P-P interval (P-P = 0.84 sec) to the shorter P-P' interval (P-P = 0.40 sec) and make the correct diagnosis of non-conducted atrial bigeminy simulating a second-degree AV block with 2:1 conduction.