Significance of Left Posterior Wall
There are reasons why PW of the left atrium needs to be included when
ablation of persistent AF is planned. First, LPW shares the same
embryological origin of PVs and, thus this implies that the two
structures are intertwined, potentially favoring creation of different
and complex circuits. In this respect, it is worth mentioning that as
the left atrium (LA) develops, the PVs represent on outgrowth tissue of
the LPW. This explains why the embryologic origin of LPW and PVs can
provide the anatomic basis for the development of atrial arrhythmias
and, in particular of AF (2,3). Second, the specific electrophysiologic
characteristics of atrial myocytes within the LPW can play a role. As a
matter of fact, LP atrial myocytes have a higher incidence of delayed
after depolarizations and larger late sodium currents in addition to a
larger intracellular Ca transients and sarcoplasmic reticulum Ca
contents. A smaller protein expression of the Na-Ca exchanger has been
also found. This can promote a higher propensity to arrhythmogenic
behavior and lead to distinctive electrophysiological properties that
may contribute to the pathophysiology of AF (4). Third, LPW in patients
with persistent AF is an ideal anatomic location for significant atrial
remodeling, comprising fibrosis and lymphomononuclear infiltration
(5,6). Moreover, spontaneous trigger activity and so “called” rotors
have been previously reported in persistent AF patients (7,8).
Therefore, since secondary triggers and more complex atrial circuitries
take place in LPW, it appears reasonable that their elimination may be a
crucial adjuvant strategy for providing a better clinical outcome.