Mohammad Alasti, MD, Abolfath Alizadeh, MD, Amirfarjam Fazelifar, MD,
Mohammad Ali Sadr-Ameli, MD
Department of Pacemaker and Electrophysiology, Rajaie Cardiovascular
Medical Center, Vali-asr Avenue, Tehran, IRAN.
Address for
correspondence: Mohammad Alasti, M.D., Department of Pacemaker
and Electrophysiology, Rajaie Cardiovascular Medial Center, Vali-asr
Avenue, Tehran, IRAN. E Mail: alastip@gmail.com
Key Words: His-purkinje system;
infra-his block
A 55 year old man with history of
palpitation was referred for electrophysiologic study. Baseline ECG,
physical examination and transthoracic echocardiographic study
were normal. Electrophysiologic study revealed normal AH and HV
intervals. Pacing of right atrium with a cycle length of 300 msec
showed 2:1 AV block. AH interval was 252 msec and the block was
infra-his (
Figure 1). With
continual of right atrial pacing, one to one AV conduction with
increasing AH interval to 282 msec and QRS widening (LBBB pattern) were
being observed. HV intervals during 2:1 block and during 1:1 AV
conduction were normal. What is the mechanism? Is it an abnormal
finding in this patient?
Figure 1
During 2:1 AV
conduction, AH interval was 252 msec and conducting system below His
was in absolute refractory period so the impulse could not propagate
and infra-his block occurred. After increasing of AH interval to 282,
the conducting system below His had enough time to enter the relative
refractory period. So AH conduction delay permitted transition from 2:1
AV conduction to 1:1 AV conduction. Infra-his block can be
produced at paced cycle lengths of less than 400 msec in normal
His-purkinje system and is not considered abnormal in this case.
