Many individuals with ME/CFS have postural orthostatic tachycardia syndrome (PoTS). PoTS is not just a condition that causes tachycardia (increased heart rate), rather individuals with PoTS have a myriad of other symptoms, such as cognitive difficulties, temperature sensitivity and gut problems. Whilst multiple mechanisms have been recognised, the pathophysiology of PoTS is still not fully understood.
Hence, as a step towards better understanding, a research team explored the haemodynamic profiles (assessment of blood flow) of 233 individuals with ME/CFS and co-occurring PoTS, 507 individuals with ME/CFS without PoTS, and 48 healthy controls. This involved measuring the heart rate, blood pressure and stroke volume index (amount of blood pumped by the heart) of participants during a tilt-table test (assessment for PoTS). A tilt table test checks how an individual’s body reacts to a change in position from horizontal to upright. In PoTS it is expected that there will be an abnormal heart rate-blood pressure response upon assuming an upright position (or at least an abnormal heart rate increase).
Findings
Interestingly, the researchers noted two subgroups amongst individuals with ME/CFS and concurrent PoTS. With those with a limited heart rate increase (between 30-39 beats per minute), mainly increased venous pooling (accumulation of blood, particularly in lower limbs) was observed. With those with a larger heart rate increase (over 40 beats per minute), the data suggested a hyperadrenergic response, i.e. exaggerated activation of the sympathetic nervous system. According to the researchers, this opens the door to the possibility of tailoring PoTS treatments according to the profile. Those with limited heart rate increase could benefit from interventions aimed at increasing blood volume, such as increasing water/salt intake and fludrocortisone (steroid). Those with the larger heart rate increase may preferably be treated with beta blockers (heart rate control medication).
Limitations
Patients were from a single centre (rather than more multiple sites); therefore, the study should be replicated elsewhere. The researchers also acknowledged there could have been referral bias as a result of GPs selectively referring patients with certain symptoms. Additionally, the study did not enrol individuals who were bedbound.
