Brain and heart connections: The trigeminocardiac reflex!

Abstract

Trigeminocardiac reflex (TCR) is a well-established neurogenic reflex although its exact mechanism and clinical significance remain unclear. This reflex may be incited by stimulation of the trigeminal nerve anywhere along its course starting from the peripheral distribution to the central nucleus. It usually manifests as bradycardia, asystole, hypotension, apnoea and gastric hypermotility; though other clinical manifestation such as tachycardia and hypertension may also occur. Diving reflex (DR) shares many similarities with TCR in both clinical manifestation and mechanism of action and is often considered as a modified or subtype of TCR. DR is an important physiological adaptation to withstand hypoxia during apnoea in many animal species including humans and thus belongs to a group of oxygen-conserving reflexes. Although TCR is a physiological reflex having protective function, an exaggerated response may have fatal consequences. Surgeries or stimulation involving head, neck and face region (area supplied by trigeminal nerve) are particularly prone to provoke this reflex. Vigilant and continuous monitoring for early identification of warning signs and communication with surgeon to interrupt the stimulus immediately is enough to cease the reflex in most of the cases. However, failure to identify and treat in time may have deleterious consequences and thus TCR has gained much attention and awareness in recent years. Over the last two decades, our knowledge on TCR has expanded but we still remain far from complete elucidation of pathophysiology, mechanism and clinical significance of this unique ‘brain and heart connection’ called TCR.

Keywords

• bradycardia
• hypotension
• neurosurgery
• trigeminocardiac reflex