Open Journal of Internal Medicine, 2012, 2, 34-36 OJIM
http://dx.doi.org/10.4236/ojim.2012.21008 Published Online March 2012 (http://www.SciRP.org/journal/ojim/)
Electrophysiologic behaviour of a left sided accessory
pathway with decremental (Mahaim-like) properties
Marco Galeazzi, Maurizio Russo, Sabina Ficili, Carlo Lavalle, Claudio Pandozi
Dipartimento Cardiovascolare, Ospedale San Filippo Neri, Rome, Italy
Received 13 September 2011; revised 10 November 2011; accepted 17 January 2012
ABSTRACT
The observation of a left sided accessory pathway
with decremental properties is rare. We describe the
behaviour of one of these pathways which was cha-
racterized by the presence of retrograde conduction
(not previously reported) and thus inducibility of
atrio-ventricular orthodromic reentrant tachycardia.
Keywords: Accessory Pathway; Decremental Properties
1. INTRODUCTION
A 52 year-old male was admitted to our cardiology de-
partment complaining recurrent episodes of palpitation.
The ECG pattern showed sinus rhythm with PR interval
80 msec and signs of minimal ventricular pre-excitation.
The electrophysiologic study showed a left lateral eccen-
tric and decremental retrograde conduction. During pro-
grammed right atrial stimulation, antegrade long con-
duction times were detected, along with a progressive
leghtening of the A-H interval, a contemporary short-
ening of the H-V interval and a progressive pre-excita-
tion of QRS complexes with right bundle branch block
(RBBB) morphology (Figures 1(a)-(b)). The earliest
ventricular activation was observed at the level of the
distal dipoles of the coronary sinus diagnostic catheter,
Figure 1. Electrophysiologic study; programmed right atrial stimulation (S0 - S0 500 msec; S0 - S1 320 msec).
Leghtening of the spike (*)-H interval, contemporary shortening of the H-V interval (H wave moving inside
the slow initial component of V wave), and progressive pre-excitation of QRS complexes with a right bundle
branch block (RBBB) pattern are visible (1(a) and 1(b) [details]). The earliest ventricular activation (details
in 1(c)) occours at the level of CS 3 - 4 (one of the distal dipoles of the coronary sinus diagnostic catheter, red
circle), thus suggesting the presence of a left lateral accessory pathway with decremental properties. HRA =
High Right Atrium; HBEd and HBEp = His Bundle catheter Electrodes distal and proximal, respectively;
RVA = Right Ventricular Apex; DCS = Distal Coronary Sinus; PCS = Proximal Coronary Sinus; * = spike.

M. Galeazzi et al. / Open Journal of Internal Medicine 2 (2012) 34-36 35
thus suggesting the hypothesis of a left lateral accessory
pathway with decremental properties (Figure 1(c)).
During these manouvers, two different arrhythmias
were induced. The former was an antidromic atrio-
ventricular reentrant tachycardia with RBBB morpho-
logy (cycle lenght 248 msec); the site of the earliest
ventricular activation was confirmed to be at the level of
the left lateral wal l ( Figure 2). The latter was an orthod-
romic atrio-ventricular reentrant tachycardia with
normal QRS morphology and late progression to an
aberrant, RBBB-like ventricular conduction (cycle lenght
282 msec); also the earliest site of the atrial back-
activation was detected at the level of the left lateral wall
(Figure 3).
The mitral ring electrical mapping in sinus rhythm
allowed the earliest ventricular activation to be recorded
at the level of the left lateral wall. The accessory path-
way was successfully ablated.
2. DISCUSSION
In 1938, Mahaim firstly described the existence of car-
diac nodo-ventricular conduction fibres [1]. The behavi-
our of these fibres (which are now actually known to be
atrio-fascicular or atrio-ventricular) is characterized by
antegrade decremental conduction, minimal or no pre-
excitation during sinus rhythm, absence of retrograde
conduction over the accessory pathway, partecipation of
the atrium in the antidromic reentrant tachicardia and
responsiveness to adenosine. Most of these fibres have
been described in the right atrium, although several
works do exist concerning the observation of Mahaim-
like properties in some left sided accessory pathways
[2-7]. Indeed, the electrophysiologic properties of the
pathway we describe are not fully compatible with the
Mahaim fibres behaviour. The original finding is that a
retrograde conduction along the pathway was present, as
confirmed by both the basal ventricular stimulation and
the induction of an orthodromic reentrant atrio-ventri-
cular tachycardia. Such observation is quite rare and has
been previously reported only in a right sided accessory
pathway [2].
3. CONCLUSION
Although quite rare, findings of retrograde conduction
Figure 2. Antidromic atrio-ventricular reentrant tachycardia with RBBB morphology (cycle lenght 248 msec); the site of the ear-
liest ventricular activation is detectable at the level of the left lateral wall (red circle). HRA = High Right Atrium; RVA = Right
Ventricular Apex; DCS = Distal Coronary Sinus; PCS = Proximal Coronary Sinus.

M. Galeazzi et al. / Open Journal of Internal Medicine 2 (2012) 34-36 36
Figure 3. Orthodromic atrio-ventricular reentrant tachycardia with normal QRS morphology and late progression to an aberrant,
RBBB-like ventricular conduction (cycle lenght 282 msec, red star); the earliest site of the atrial back-activation is detectable at the
level of the left lateral wall (CS 3 - 4). HRA = High Right Atrium; DCS = Distal Coronary Sinus; PCS = Proximal Coronary Sinus.
properties in left sided accessory pathways with decre-
mental properties are possible and must be taken into
account in the differential diagnosis process concerning
orthodromic atrio-ventricular reentrant tachycard ias.
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