The Trigeminal Cardiac Reflex

The Trigeminal Cardiac Reflex:

Kratschmer was first to describe cardiac arrhythmias on upper airway stimulation in 1908. Since then there has been a steadily growing body of literature on the TCR. It is considered the most powerful of the many cranial reflexes and has been attributed to many negative surgical outcomes and even sudden infant death syndrome. Most regions result in a very rapid and significant drop in heart rate, blood pressure, respiration, gastric motility, and acid production. In some cases, the heart rate and blood pressure drop so low that the patient does not survive the procedure.

It is medically accepted that there must be a change in heart rate of greater than 20% before it may be stated the TCR was involved.

The TCR has been reclassified into 6 major regions of stimulation. Each has been given a unique name but all share similar characteristics.

 

The Occulo-Cardiac Reflex: Parasympathetic Stimulation

This region of stimulation is around or behind the eye socket. Pressure on the eyeball can also stimulate the TCR in this region.

Figure 1: The Occulo-Cardiac Reflex results in parasympathetic stimulation resulting in bradycardia, hypotension, hypopnea, increased gastric motility, increased acid production in the stomach.

 

The Naso-Cardiac Reflex: Parasympathetic Stimulation

The region of stimulation is the nose area. Local anesthetic placed into the nose can sometimes activate this reflex as does surgery involving the nose region.

Figure 2: The Naos-Cardiac Reflex results in parasympathetic stimulation resulting in bradycardia, hypotension, hypopnea, increased gastric motility, increased acid production in the stomach.

 

The Gasserion Ganglion Reflex: Sympathetic Stimulation

This may be triggered by sleep-related bruxism or by surgery in the region of the Gasserion ganglion. This is the only region that triggers a sympathetic response. Interestingly, restless leg syndrome also results in activation at this level resulting in sympathetic stimulation. The acid reflux of GERD combined with the extreme tooth grinding of sleep-related bruxism accelerates tooth wear from the acid softening the enamel.

Figure 3: The Gasserion Ganglion Reflex results in sympathetic stimulation resulting in tachycardia, hypertension, hyperpnea, increased gastric motility, increased acid production in the stomach. Sleep-related bruxism affects the TCR at this level.

The  Maxillo-mandibular Reflex: Parasympathetic stimulation

There are a number of regions that are involved. Surgery of either the maxilla or mandible or endodontic procedures involving the cuspids or 1st bicuspid may trigger this.

Figure 4: The Maxillo-mandibular Reflex results in parasympathetic stimulation resulting in bradycardia, hypotension, hypopnea, increased gastric motility, increased acid production in the stomach.

 

The Central Reflex: Parasympathetic Stimulation

Surgery involving this region of the brainstem can result in stimulation of the TCR.

Figure 5: The Central Reflex results in parasympathetic stimulation resulting in bradycardia, hypotension, hypopnea, increased gastric motility, increased acid production in the stomach.

 

The Brainstem Reflex: Parasympathetic Stimulation

Surgery involving this region of the brainstem can result in stimulation of the TCR.

Figure 6: The Brainstem Reflex results in parasympathetic stimulation resulting in bradycardia, hypotension, hypopnea, increased gastric motility, increased acid production in the stomach.

 

The TCR is considered to be the most powerful of the many cranial reflexes and head and neck surgeons deal with this regularly. The drop in heart rate and blood pressure is life-threatening and may be fatal in some cases. There are numerous case studies describing near fatalities during various surgeries in the region of the trigeminal nerve.

In addition to the six above reflexes, two more subtypes have been identified recently. The first, the Photic reflex, occurs as a sneeze when looking at a bright light. This is considered a subtype of the Occculo-Cardiac reflex. The second, TCR activation during non-surgical endodontic procedures on cuspids and 1st bicuspids, is considered to be a subtype of the Maxillo-Mandibular reflex. There will likely be other subtypes described in the future as the trigeminal nerve is the largest of the cranial nerves with an extensive innervation in the head and neck.