Anterior Mitral Lines
The anterior mitral line may extend from the superior aspect of the
mitral valve to the RSPV, a roof line or more laterally to the LSPV. The
major advantage of this approach is that it avoids the epicardial
connections of the CS muscle coat and bundle of Marshall. However, this
approach is also associated with several anatomic challenges. The
anterior mitral line is significantly longer than the lateral mitral
isthmus line.30 Furthermore, thick epicardial muscle
bundles within Bachmann’s bundle that extend anteriorly and invaginate
the base of the LAA can make transmural ablation difficult. As opposed
to the lateral line there is no ready access to the epicardial aspect of
the anterior line. Finally, anterior mitral line ablation results in
greater activation delay of the LAA compared with lateral mitral isthmus
lines with some case reports describing transient ischaemic attacks and
strokes in patients post anterior linear ablation despite appropriate
oral anticoagulation.30,31 If performed in conjunction
with a lateral mitral isthmus line or in the presence of posterolateral
scar, the LAA may become electrically isolated with a consequent
increased risk of thromboembolic events.32 Regarding
the choice between an anterolateral or anteromedial line, the
anterolateral line courses across the region of maximal myocardial
thickness 14,33 Conversely, imaging studies have noted
that ridges and diverticuli are found most frequently along the
anteromedial ablation line making adequate contact and contiguous
transmural ablation along this line difficult to
achieve.33 While the sinus node artery branch of the
left circumflex artery may be found in close proximity to both the
anteromedial and anterolateral lines, it is most commonly found nearer
to the anteromedial line.33 Generally the course of
the anterior line is directed through the shortest route from the
superior mitral valve transecting the region of low voltage towards a PV
or roof line (see Figure 2).