Figure 1:

Proposed pathophysiological mechanisms for postural orthostatic tachycardia syndrome (POTS). The blue boxes indicate processes that may lead to reduced circulating blood volume, impaired venous return on standing and reflex orthostatic tachycardia. The red boxes indicate primary processes affecting sinus node response to orthostatic challenge and abnormal chronotropic response on standing. Different mechanisms may overlap. For example, autoantibodies that target cardiac receptors may produce an abnormal response during orthostasis, whereas those that target vascular receptors may lead to venous pooling, relative hypovolemia and reflex tachycardia on standing. Note: EDS = Ehlers–Danlos syndrome, MCAS = mast cell activation syndrome, RAAS = renin–angiotensin–aldosterone system.