However, patients with grade 2 or 3 uptake had structural and functional features on echocardiogram typical of amyloid infiltration, which were associated with significantly elevated serum NT-proBNP concentrations (median, 650 ng/L; IQR, 320-1095 ng/L; P < .001) and a higher rate of atrial fibrillation (30.4% [112 patients] vs 19.8% [23 patients with grade 1 uptake]; P = .03). This evidence concerns the gene NPPB and atrial fibrillation.