However, none of these exhibited high differential expression, with the exception of KRT19 identified from the rat microarray study [23], which showed approximately a 20-fold increase in NP cells compared with AC and AF cells, and KRT18 and NCAM1 identified from the canine microarray study [24], which demonstrated 1860-fold and 10-fold higher expression in the NP cells than AF or AC cells, respectively. This evidence concerns the gene KRT18 and atrial fibrillation.