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).