Short QT interval
A short QT interval shows up in an electrocardiogram (EKG) rarely in the general population but frequently in chronic fatigue syndrome (CFS) patients with dysautonomia. One study concluded that a short QT interval was presented in CFS patients but not fibromyalgia patients and thus could be used as a way to distinguished between the two illnesses. Another study done in 2012 used a formula to give a corrected QT interval adjusted for variations in heart rate, calling it QTc, which was able to differentiate between ME/CFS, non-CFS fatigued and control populations so consistently, it was suggested as a possible biomarker.
- 2012, Shortened QTc interval in chronic fatigue syndrome
"Abstract - Chronic fatigue syndrome (CFS) is a common, debilitating disease that is frequently associated with autonomic dysfunction. One previous study of a selected population using a manual measurement technique suggested CFS is associated with a shortened QTc [QT corrected] interval. Here we assessed QTc in a large UK population of CFS patients using automated, clinically applicable, measurement techniques and confirmed that QTc is significantly shortened in CFS patients compared to non-CFS fatigued and control populations. Automated measurement of QTc in clinical practise has potential utility as a diagnostic biomarker in CFS."
- 2008, 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<0.0001); the supine QTc cut-off <385.7 ms was 79% sensitive and 87% specific for CFS vs. FM. The average QTc at the 10th minute of tilt was 409 ms (SD 18) in FM versus 367 ms (SD 21) in CFS (p<0.0001); the tilt QTc cut-off <383.3 ms was 71% sensitive and 91% specific for CFS vs. FM. The average HIS in FM patients was -3.52 (SD 1.96) versus +3.21 (SD 2.43) in CFS (p<0.0001). 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." 
- 2006, Shortened QT interval: a distinctive feature of the dysautonomia of chronic fatigue syndrome.
"Abstract - PURPOSE: Because autonomic nervous functioning is frequently abnormal in chronic fatigue syndrome (CFS), we examined whether the corrected QT interval (QTc) in CFS differs from QTc in other populations. METHODS: The QTc was calculated at the end of 10 minutes of recumbence and the end of 10 minutes of head-up tilt. In a pilot study, groups of 15 subjects, CFS, and controls, matched for age and sex, were investigated. In a second phase of the study, the QTc was measured in larger groups of CFS (n = 30) and control patients (n = 96) not matched for demographic features. RESULTS: In the pilot study, the average supine QTc in CFS was 0.371 +/- 0.02 seconds and QTc on tilt, 0.385 +/- 0.02 seconds, significantly shorter than in controls (P = .0002 and .0003, respectively). Results of phase II confirmed this data. CONCLUSIONS: Relative short QTc intervals are features of the CFS-related dysautonomia. The significance of this finding is discussed."
- Naschitz, J; Slobodin, G; Sharif, D; Fields, M; Isseroff, H; Sabo, E; Rosner, I (2008), "Electrocardiographic QT interval and cardiovascular reactivity in fibromyalgia differ from chronic fatigue syndrome.", European Journal Internal Medicine, 19 (3): 187-91, PMID 18395162, doi:10.1016/j.ejim.2007.08.003
- Scott, Ashley; Norton, Michael; Mabillard, Holly; Newton, Julia (2012), "Shortened QTc interval in chronic fatigue syndrome" (PDF), Bulletin of IACFS/ME, 19 (3/4): 202-211
- Naschitz, J; Fields, M; Isseroff, H; Sharif, D; Sabo, E; Rosner, I (2006), "Shortened QT interval: a distinctive feature of the dysautonomia of chronic fatigue syndrome.", Journal of Electrocardiology, 39 (4): 389-94, PMID 16895768, doi:10.1016/j.jelectrocard.2005.10.014