OI and CI in ME
Orthostatic intolerance and chronotropic incompetence in patients with Myalgic Encephalomyelitis or Chronic Fatigue Syndrome, by K Miwa in Circulation Reports 2023; 5: 55–61 [doi:10.1253/circrep.CR-22-0114]
Research abstract:
Orthostatic intolerance is a common symptom in ME/CFS, and the symptoms induced by sitting or standing can leave patients bedridden.
Chronotropic incompetence (CI) refers to the inability of the heart to increase its beat rate to a level that is proportionate to the activity being undertaken, or a reduced increase in heart rate during activity.
Previous studies have observed CI in ME/CFS patients. This study aimed to explore the role of POTS and CI in ME/CFS patients during orthostasis.
The recordings of 101 ME/CFS patients (International Consensus Criteria) who completed an active 10-minute standing test at least 3 times from July 2017 to December 2020 at the Miwa Naika Clinic (Japan) were included in this study.
This test involved recumbent rest for 5 minutes, and then standing with feet shoulder width apart for 10 minutes. Inability to reach 10 minutes was recorded as a failure, and postural orthostatic tachycardia syndrome (POTS), orthostatic hypotension or neurally mediated hypotension, were subsequently diagnosed depending on symptom and heart rate responses to the test.
CI was considered positive if a patient failed the test without POTS but, succeeded with POTS on other attempts.
The authors found that 13 participants completed standing tests with and without exhibiting POTS, whilst also completing and failing the test on different occasions. Of these patients, they were categorised as CI positive if test success occurred with POTS and test failure occurred without POTS being exhibited. Amongst these 13 patients, the authors found that 92% were CI positive, and 38% exclusively failed the test without experiencing POTS.
The authors conclude that these results demonstrate that the presence of POTS in ME/CFS patients is essential for the maintenance of orthostasis during 10-minute standing tests. The authors also conclude that some ME/CFS patients experience CI during standing tests, suggesting the presence of impaired sympathetic activation.
