1. INTRODUCTION
The mitral isthmus (MI) is the anatomical area between the ostium of the
left inferior pulmonary vein (PV) and the posterolateral part of the
mitral valve annulus. Mitral isthmus ablation is an established strategy
in the treatment of perimitral atrial flutter (PMF) [1, 2] as well
as an adjunct to pulmonary vein isolation (PVI) in the treatment of
non-paroxysmal atrial fibrillation (AF) [3,4].
The usefulness of the MI ablation and generally of linear lesions is
questionable as an initial strategy in persistent AF ablation [5,6].
However, it is one of the possible options in cases where PVI alone is
not considered sufficient, such as in redo cases with well-maintained
PVI [7], long-lasting persistent AF [8,9], or diseased
myocardium with low-voltage electrical activity [10]. On the other
hand, MI ablation is an effective therapy for PMF, however, these
reentrant tachycardias can also be treated by ablating critical
isthmuses with slow conduction zones [11-13].
If a linear lesion is attempted in the ΜΙ, the creation of complete and
bidirectional block is very important. Failure to achieve bidirectional
block can be proarrhythmic and therefore if it cannot be achieved it
should not even be attempted [14-16]. The anatomical complexity of
the MI hinders the creation of transmural lesions [17]. This can
lead to the persistence of conduction gaps that allow the maintenance of
PMF despite the apparent evidence of complete block. This is a condition
often referred to as MI pseudo-block [18-21].
In this prospective study, we investigated clinical and
electrophysiological characteristics of patients who had undergone MI
ablation, focusing in particular on the group of patients who continued
to have PMF, while MI block had been previously demonstrated by
evidentiary pacing maneuvers. At the same time, we tried to peruse
standard PMF circuits by measuring conduction velocities, in order to
understand the specific electrophysiological properties of these
reentrant tachycardias and to improve our knowledge in selecting the
most appropriate PMF ablation strategy.