PCSK9 and atrial fibrillation: We found that PCSK9 was detectable in the serum, AF and the spinal cord and placenta in the same form, which revealed one band (60 kDa) in the spinal cord and two bands (60 and 50 kDa) in the serum, AF and placenta (Fig. 5c).Immunohistochemistry (IHC) showed PCSK9 expression was higher on the fetal side of the placenta than on the maternal side.