Orthostatic chronotropic incompetence in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

Abstract

BACKGROUND: Orthostatic intolerance (OI) is a core diagnostic criterion in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The majority of  ME/CFS patients have no evidence of hypotension or postural orthostatic  tachycardia syndrome (POTS) during head-up tilt, but do show a significantly  larger reduction in stroke volume index (SVI) when upright compared to controls.  Theoretically a reduction in SVI should be accompanied by a compensatory increase  in heart rate (HR). When there is an incomplete compensatory increase in HR, this  is considered chronotropic incompetence. This study explored the relationship  between HR and SVI to determine whether chronotropic incompetence was present  during tilt testing in ME/CFS patients. METHODS: From a database of individuals  who had undergone tilt testing with Doppler measurements for SVI both supine and  end-tilt, we selected ME/CFS patients and healthy controls (HC) who had no  evidence of POTS or hypotension during the test. To determine the relation  between the HR increase and SVI decrease during the tilt test in patients, we  calculated the 95% prediction intervals of this relation in HC. Chronotropic  incompetence in patients was defined as a HR increase below the lower limit of  the 95th % prediction interval of the HR increase in HC. RESULTS: We compared 362  ME/CFS patients with 52 HC. At end-tilt, tilt lasting for 15 (4) min, ME/CFS  patients had a significantly lower SVI (22 (4) vs. 27 (4) ml/m(2); p < 0.0001)  and a higher HR (87 (11) vs. 78 (15) bpm; p < 0.0001) compared to HC. There was a  similar relationship between HR and SVI between ME/CFS patients and HC in the  supine position. During tilt ME/CFS patients had a lower HR for a given SVI; 37%  had an inadequate HR increase. Chronotropic incompetence was more common in more  severely affected ME/CFS patients. CONCLUSION: These novel findings represent the  first description of orthostatic chronotropic incompetence during tilt testing in  ME/CFS patients.