Aims

The modified anterior line (MAL) has been described as an alternative to the mitral isthmus line. Despite better ablation results, achieving a bidirectional line block can be challenging.  We aimed to investigate the ablation values to determine a scar on cardiac magnetic resonance (CMR) imaging 3 months after MAL ablation.

Methods

Twenty four consecutive patients who underwent a MAL ablation have been included. The indication for MAL was perimitral flutter (n= 6) or substrate ablation for diffuse anterior left atrial (LA) low-voltage area in persistent atrial fibrillation (AF) (n=18). The MAL was divided into three segments: segment 1 (S1) from mitral annulus to height of lower begin of left atrial appendage (LAA) antrum; segment 2 (S2) height of lower begin of LAA antrum to end of upper LAA antrum; segment 3 (S3) from end of upper LAA antrum to left superior pulmonary vein. Ablation was performed using a contact force catheter, automated lesion tagging and Ablation Index (AI). AI target was left to the operator’s choice. An inter-lesion distance of ≤ 6mm was recommended. The bidirectional block was systematically evaluated at the end of procedure. All patients underwent a CMR study at 3 months, regardless of symptoms, to identify myocardial lesions (scar).

Results

Bidirectional MAL block was achieved in all patients. CMR imaging revealed scar in 45 of 72 (63%) segments. In all three segments of MAL, ablation time and Ablation Index were significantly larger in scar areas compared to non-scar areas. The mean AI value to detect a scar was 502±47 in S1, 485±60 in S2 and 460±64 in S3. The mean ablation time to detect a scar was 22±7sec in S1, 23±8 sec in S2 and 22±8 sec in S3. Mean contact force and impedance drop were not significantly different between scar and non-scar areas.

Conclusion

AI values and ablation time are critical parameters that determine durable atrial scar. Different AI targets are required for each segment of the MAL to achieve effective transmural lesions.