POTS is defined by a sustained increase in heart rate of 30 bpm or more on standing, without a drop in blood pressure — driven by multiple possible mechanisms including cerebral hypoperfusion, blood pooling in the lower body, low plasma volume, baroreflex dysfunction, and hyperventilation-driven hypocapnia. It is not a single disease but a syndrome: a convergent endpoint reached by different physiological pathways in different patients.
The most important reframing in the POTS literature is the direction of causality: cerebral blood flow drops before heart rate rises. The tachycardia is a compensatory response to the perfusion failure, not the cause of symptoms. This single finding reorganizes the condition — the heart is not the primary problem, the brain's blood supply is.
A second key finding is that heart rate elevation does not predict symptom severity. Patients can have a modest tachycardia and feel severely ill; others can mount a large rate response and function near normally. Symptoms track more closely with cerebral perfusion than with heart rate. This has direct implications for diagnosis, monitoring, and treatment response.
Treatment must match the underlying mechanism — what works for low-volume POTS differs from what works for hyperadrenergic or neuropathic POTS. Salt and fluid loading, compression garments, recumbent exercise protocols, beta-blockers, fludrocortisone, and midodrine all have evidence in specific subtypes. Identifying which mechanism is driving the syndrome in a given patient is the necessary first step before selecting any intervention.