Abstract Body: Background: Atrial fibrillation (AF) remains the leading cause of arrhythmia and has significant associated morbidity. Despite advances in treatment of AF, a mechanistic understanding of arrhythmia drivers in cardiomyocytes is lacking. We hypothesize that cardiomyocyte senescence may drive AF with associated atrial fibrosis.

Methods: Using spatial transcriptomics, differences in the transcriptome of human left atrial posterior wall tissue of individuals with no AF (no-AF), AF without catheter ablation (CA) (AF-noCA), and AF with CA (AF-CA) were determined. 10X Visium HD platform was used, and analysis was completed using packages including: scanpy, bin2cell, and celltypist. Analysis was completed to determine cell annotations and unbiased clustering of transcripts. Differential gene expression (DGE) was determined of cardiomyocyte clusters. Tissues were evaluated with H&E and Mason’s Trichrome stain (MTS).

Results: Results for the cardiomyocyte (CM) cluster was further evaluated and revealed two major subclusters (CM1 and CM2) (Figure 1). Both no AF and AF-CA CMs had similar DGE and were significantly different from AF-noCA CM. CM1 was enriched for transcripts related to senescence (GAS7, CLU, PDK4, SERPINE1); these markers were significantly upregulated only in the AF-noCA group. Functional changes in CM defined the CM2 cluster, with transcripts showing significant DGE including MYL7, ACTC1, DES, TNNT2, TPM1, MYH7, TNNI3, MYL4, TNNC1, MYL2, and NPPA. These transcripts were notably upregulated in no AF and AF-CA groups but not in AF-noCA CMs. Collectively, these show a more robust CM transcriptome with likely improved CM function. Total CM proportions were weighted towards this functional CM2 subgroup in no-AF patients and shifted towards the senescence-defined CM1 subcluster in AF-noCA patients. AF-CA patients, however, showed a rebalancing towards CM2 (Figure 2). MTS staining confirmed increased fibrotic areas in AF-noCA and AF-CA, with CM1 expression increased in AF-CM.

Conclusion: We find distinct atrial CM clusters present in no-AF, AF-noCA, and AF-CA. There is a signal for senescence associated with AF resulting in significant shift in CM function and phenotype which is rescued with CA, suggesting this intervention may help to return non-ablated regions of the LA closer to a no-AF transcriptome. Further investigation will allow identification of molecular mechanisms driving these transcriptional changes.