68 Chapter 3 For that reason, only the raw data on frontal T-axis over time were visually displayed in a polar plot. The GLM assumes a linear change in ECG parameters over time, and is therefore unsuitable for making an accurate statement about the age at which an ECG parameter in FD patients start to deviate from those in control subjects. To study the timeframe in which ECG alterations occur in FD, the differences in absolute values for each ECG parameter between FD patients and the control subjects for each decade of adult life were assessed by a Wilcoxon rank test. For these comparisons, a Bonferroni adjusted p- value is displayed to correct for multiple testing. For this comparison of absolute values, only the last available ECG per patient per decade was selected to ensure that the influence of repeated measurements in single individuals was limited. By using a Spearman correlation analysis, the correlation between the seven electrophysiological parameters on the last obtained ECG and LVMi on the corresponding CMR was evaluated. A Wilcoxon signed-rank was used to study if the absolute values of the parameters on the last ECG were different between patients with and without LGE on the corresponding CMR (LGE assesses the presence of myocardial fibrosis). We regarded a p-value ≤0.05 as statistically significant. Results Participants’ characteristics Serial ECGs of a total of 133 patients with classical FD (36% men and 64% women) were included averaging 15 ECGs per patient (range: 4-66), totaling 1,995 ECGs. For the FD patients, the median age at last obtained ECG was 48 years (range: 19-82). The HELIUS cohort consisted of 3,893 control subjects (43% men and 57% women) with a median age of 46 years (range: 18-71). Full description of the participants’ characteristics can be found in table 1. Eighty percent (106/133) of the included FD patients were treated with ERT, during a median period of 7 years (range: 0-17). ERT initiation decisions were based on the presence of FD symptoms [29] or on recommendations by the European Fabry Working Group after these became available in 2015 [15]. See supplemental table 4 for the GLA mutations characteristics of the FD patients.
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