82 Chapter 3 distinguishes patients with and without fibrosis was the spatial QRS-T angle, where 51 out of 53 FD patients (96%) without LGE had a normal QRS-T angle (between 0 ° and 105 °) (supplemental figure 9). Discussion This is the first long-term longitudinal study in classical FD patients that assessed the evolution of electrophysiological depolarisation, repolarisation and their interaction. In addition, we could include ECGs from a large cross-sectional sample of apparently healthy control subjects, enabling a comparison across a wide age range. The results show that for the studied ECG parameters, the differences between FD patients and controls increase with ageing. These parameters differ from the included control cohort, both in terms of rate of progression as well as absolute values, but they often fall within generally accepted reference ranges and may therefore not be recognized as abnormal. This is particularly true for the PRinterval and frontal QRS-axis. PR-interval has long been considered a hallmark of FD [33], but both in this study, as well as the study by Namdar et al, the absolute values of PR-intervals for most FD patients fall within the reference range (120-200 ms) [30] [34]. Perhaps the most important result of this study is that for all ECG parameters studied, it is not so much the absolute value, but the rate of change over time that clearly distinguishes the FD patients (especially at younger age) from the control subjects (figure 1-4). This likely represents progression of cardiac disease since: a) the course is very different from that of controls with cardiovascular risk factors, b) there is a clear association between the ECG parameters and other established markers of cardiac disease (left ventricular hypertrophy and the presence of fibrosis as assessed by CMR) and c) in studies in both the general population [31, 35-37] and patients with other cardiac disorders [38-40] abnormal values of ECG parameters are known to be associated with higher risk of cardiac complications. Considering the described differences in the rate of change between FD patients and controls from the general population, we suggest that monitoring the rate of change in FD patients with still apparently ‘normal’ ECGs might be a suitable way, in combination with echocardiography, CMR and biochemical markers, to detect early signs of cardiac involvement in FD. Surprisingly, for several parameters the rate of change in female patients was comparable and sometimes even more pronounced compared to male patients
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