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Figure 1 Multidimensional scaling (MDS) and similarity matrix/exact test demonstrating clear and significant effect of left ventricular assist device (LVAD) support on gene expression. (A) All gene expression data for pre-LVAD (green) and post-LVAD (red) patients (6,800 average difference values from Affymetrix per patient) were subjected to MDS using Pearson dissimilarities. The image represents convergence of the MDS algorithm, stress (measure of image validity) = 0.03. (B) Similarity matrix based on the Pearson correlation of the 12 samples (6 pre- and 6 post-LVAD). Following an exact test (random combinations of the 12 samples assigned to two groups), the most significantly divergent was the actual pre- and post-LVAD grouping, with a significance value of 0.002, illustrating the significant effect of LVAD support on gene expression.