Electrocardiographic QT interval and cardiovascular reactivity in fibromyalgia differ from chronic fatigue syndrome

Abstract Background Fibromyalgia (FM) and chronic fatigue syndrome (CFS) frequently overlap clinically and have been considered variants of one common disorder. We have recently shown that CFS is associated with a short corrected electrocardiographic QT interval (QTc). In the present study, we evaluated whether FM and CFS can be distinguished by QTc. Methods The study groups were comprised of women with FM ( n  = 30) and with CFS ( n  = 28). The patients were evaluated with a 10 min supine–30 min head-up tilt test. The electrocardiographic QT interval was corrected for heart rate (HR) according to Fridericia's equation (QTc). In addition, cardiovascular reactivity was assessed based on blood pressure and HR changes and was expressed as the ‘hemodynamic instability score’ (HIS). Results The average supine QTc in FM was 417 ms (SD 25) versus 372 ms (SD 22) in CFS ( p p p Conclusion A relatively short QTc and positive HIS characterize CFS patients and distinguish them from FM patients. These data may support the contention that FM and CFS are separate disorders.