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.