Extended Data Fig. 3: Acquisition and processing of phenotypes.

a, Fractal dimension analysis on cardiac computed tomography images. The fractal dimension was calculated using the same method as for CMR, but with manual regions of interest, in a set of gated cardiac computed tomography images. Top, analogous processing as described in Fig. 1c, using edge detection of the trabeculae and subsequent box counting across a range of sizes. Bottom, analogous to Fig. 2a, box plots of the fractal dimension measurements for 20 individuals per slice, colour-coded by cardiac region. The lower and upper hinges in the box plot correspond to the 25th and 75th percentiles (IQR), the horizontal line in the box plot indicates the median. The lower and upper whiskers extend from the hinge to the smallest and largest values that are no further than 1.5× the IQR. b, Myocardial strain. Global longitudinal Lagrangian strain at each cardiac phase for all UK Biobank participants with CMR imaging (n = 26,893). Individual data points shown with a smoothed mean and density contours. c, Principal component analysis of fractal dimension measurements across all 9 slices in the 18,096 individuals of the UK Biobank discovery cohort. Proportion of variance explained for each principal component (left). Biplot of the first and second (middle) or third and fourth (right) principal components of each individual (grey points). The corresponding loadings for the fractal dimension of slices 1–9 are shown as vectors. d, Genotype, fractal dimension and trabeculation outlines for rs35006907. Representative, registered, trabecular outlines at slice 5 are shown for the median fractal dimension of individuals with the homozygous major (blue), heterozygous (pink) and homozygous minor (green) genotypes of rs35006907. e, Pearson correlation of global fractal dimension and QRS duration (n = 18,096 individuals). QRS duration phenotype from UKB ID: qrs_duration_f12340_2_0. The Pearson correlation coefficient is indicated in the top right corner.