Supine syncope induced by needle insertion

To characterise the haemodynamic profile of supine reflex syncope triggered by a needle insertion.

This retrospective study evaluated consecutive patients with orthostatic intolerance who completed autonomic testing at Brigham and Women's Faulkner Hospital between 2016 and 2024 and developed supine syncope induced by needle insertion. Tests included deep breathing, Valsalva manoeuvre, head-up tilt and skin biopsies for small fibre quantification. We continuously recorded cerebral blood flow velocity from the middle cerebral artery using transcranial Doppler, along with end-tidal CO₂, ECG and beat-to-beat blood pressure. The skin at the leg was anaesthetised with 0.5 mL of 1% lidocaine for biopsy.

The needle insertion triggered syncope in five out of 4876 (0.1%) patients. Following a latency of 56 s, participants reported typical symptoms of cerebral hypoperfusion (light-headedness, visual change, dyspnoea) that culminated in a brief loss of consciousness. These symptoms were accompanied by a progressive decrease in heart rate, blood pressure, mean cerebral blood flow velocity, hyperventilation and widening of the transcranial signal (systolic-diastolic difference). Syncope type was mixed into two, cardioinhibition without asystole in one and cardioinhibition with asystole in two patients.

Supine syncope triggered by a needle insertion is associated with cardioinhibitory (characterised by bradycardia), vasodepressor (characterised by vasodilatory hypotension) and cerebral arteriolar vasodilatory (characterised by transcranial signal widening) responses.