Objective: Fabry patients have autonomic dysfunction but usually do not present clinically overt signs of orthostatic dysregulation. This study evaluated orthostatic regulation and baroreflex sensitivity (BRS) in untreated Fabry patients and possible baroreflex improvement with enzyme replacement therapy (ERT).
Methods: In 22 Fabry patients (aged 28W8 years), we assessed electrocardiographic RR intervals (RRIs), SBP, DBP and respiratory frequency, in supine and standing position, before and after 18 (11 patients) or 23 months (11 patients) of biweekly alpha-galactosidase A infusions (1.0 mg/kg agalsidase beta). We determined spectral powers of mainly sympathetically mediated low-frequency (0.04-0.15 Hz) and parasympathetically mediated high-frequency (0.15-0.5 Hz) RRI fluctuations, and sympathetic low-frequency powers of blood pressure fluctuations. We normalized RRI powers by relating low-frequency and high-frequency powers to total powers (low-frequency + high-frequency powers), assessed the RRI low-frequency/high-frequency ratio reflecting sympathicovagal balance. As a measure of BRS, we used the alpha-index, obtained as square root of the ratio between powers of simultaneous spectral analyses of spontaneous low-frequency variabilities in RRIs and SBP (coherence>0.5). We compared parameters in supine and standing position of untreated and treated patients with those of 15 healthy age-matched (27+/-5 years) men (repeated-measure analysis of variance, significance at P<0.05).
Results: Supine biosignals were similar in all groups. Upon standing, RRIs were lower in controls and patients after ERT than in patients before ERT (P<0.05); normalized RRI high-frequency powers as well as BRS decreased, whereas DBP, low-frequency/high-frequency ratios and sympathetic low-frequency powers of SBP increased in controls and treated patients only (P<0.05).
Conclusion: Reduced increase in heart rate, blood pressure and sympathetic activation, and limited cardiovagal withdrawal and BRS adjustment seen in untreated Fabry patients upon standing normalized after 18 and 23 months of ERT demonstrating improved baroreflex function, which, in turn, is an established parameter of improved disease prognosis.