Introduction
Ablation lines (scar regions created to block abnormal electrical conduction pathways, such as in atrial fibrillation) may become electrically transparent over time, necessitating repeat ablations. Aims/objectives: to explore the suitability of mouse models for studying trans-scar conduction after atrial cryo-ablation.
Method
Ex vivo optical mapping experiments were performed on dissected atrial preparations from cryo-injured, sham operated, and control mice (Mus musculus; on days 28 or 56, including male / female animals; n = 6 / condition). Functional whole heart optical mapping experiments were correlated with structural multiphoton imaging data to delineate scar tissue. Degree of tissue fibrosis was assessed in optically cleared hearts (X-Clarity), as well as histological tissue sections. All investigations were performed with ethical approval by the local Institutional Animal Care and Use Committee (Regierungspräsidium Freiburg, G22-047).
Results
Projecting 2D optical mapping data onto 3D multiphoton structural volume stacks of the mouse atrium, we observed passive conduction of excitation waves into the scar tissue, extending beyond the macroscopic boundaries of the border zone in all hearts after cryo-injury. These scar regions were transmural, collagen-rich, and largely devoid of cardiomyocytes. Cryo-lesions were significantly larger than the cryo-probe contact area: measured scar length was 2.73 ± 0.22 mm (compared to 1.5 mm probe length) and scar width was 1.07 ± 0.09 mm (compared to 0.23 mm probe width); lesion area was 2.01 ± 0.14 mm2 (compared to the probe area of 0.35 mm2). Values reported as mean ± SEM, unpaired t test, scar p values = 0.0002 (length), <0.0001 (width) and <0.0001 (area) compared to cryo-probe.
Conclusions
This work supports the idea of a non-myocyte mediated passive conduction of electrical excitation through atrial ablation scars. Electrical coupling of cardiomyocytes and non-myocytes may offer a potential target to steer cardiac electrophysiology post-ablation. This may ultimately reduce the need for re-ablation in patients, constituting a clinically relevant research target.