library_construction_protocol: Viable (DAPI-), metabolically active (Calcein+), nucleated (VDR+), single cells were FACS-purified from digested left atrial tissues, and subsequently loaded on a 10X Genomics Chromium Single Cell B chip as outlined by the 10X Genomics Chromium Single Cell 3' Reagent Kits v3 user guide. Libraries were prepared as outlined by the 10X Genomics Chromium Single Cell 3' Reagent Kits v3 user guide with appropriate modifications to the PCR cycles based on the calculated cDNA concentration (as recommended by 10X Genomics). Constructed libraries were validated and quantified with the Agilent High Sensitivity DNA chip and by real-time qPCR, and subsequently sequenced on an Illumina NextSeq 500 in high-output mode.