Overview of Oculocardiac Reflex
The oculocardiac reflex (OCR), also known as the Aschner reflex or trigeminovagal reflex, is a reaction that can slow down the heart rate when pressure is applied to the eyeball. This was first noticed as far back as 1908. It is generally marked by a decrease in heart rate by over 20% after the eyeball is directly pressed or if the muscles outside the eye are pulled on. However, it can also lead to lowered blood pressure, irregular heartbeat, a pause in the heartbeat, or even a complete stop in the heartbeat. This reflex is often seen during eye procedures like strabismus surgery (a surgery to correct crossed eyes), after facial injuries, during regional anesthesia, or when the eye is physically stimulated.
There’s a pretty wide range in how often OCR happens – anywhere from 14% to as much as 90% – but it’s less common as people get older. Kids are the ones who get it the most, and since they depend more on their heart rate for normal heart function, they’re also the ones who can have serious complications from it. The likelihood and severity of OCR can vary depending on things like low oxygen levels, high carbon dioxide levels, acid build-up, and the kind of anaesthetic used during surgery.
Anatomy and Physiology of Oculocardiac Reflex
The OCR arc, a pathway in our body, has two parts: the sensory (afferent) part and the action (efferent) part. Imagine the sensory part like traffic signals that send signals based on what they ‘see’ and ‘feel’, and the action part like the part of your brain that decides what action to take based on those signals.
The ‘seeing’ and ‘feeling’ part of the OCR arc is the trigeminal nerve, called the 5th cranial nerve. The action part is the vagus nerve, also called the 10th cranial nerve. This whole system gets activated when certain receptors around your eyes detect stretching.
When these signals need to be transported, it uses the short and long ciliary nerves to carry the message to a place called the ciliary ganglion. From there, the message is carried by the ophthalmic division of the trigeminal nerve to another point called the Gasserian ganglion. The final destination of the signal is the trigeminal region in the brain, known as the trigeminal nucleus. Once the signal reaches here, it triggers the action part, which sends instructions from the brain to the heart, particularly the sinoatrial node, causing it to slow down, often resulting in slower heartbeat, or bradycardia.
There are certain situations where this OCR arc can get activated. It often happens when an eye muscle, especially the medial rectus muscle, gets pulled. But research shows, no particular muscle has been significantly associated with increased activation of this OCR pathway. Other triggers can be direct pressure on the eyeball, manipulation on the eye, or pain in the eye. Even certain medical conditions like retrobulbar blocks, ocular hematomas, and facial or orbital trauma that result in increased pressure can wake up this system. However, repeated triggers tend to lessen the intensity of the response from the OCR arc.
Possible Complications of Oculocardiac Reflex
The OCR (oculocardiac reflex) is a bodily response that can sometimes result in complications. These issues can vary and often come from your body’s natural reaction to certain stimuli, guided by a part of the nervous system called the vagus nerve.
These complications can potentially include:
* Slowed heart rate (Sinus Bradycardia)
* Irregular heartbeat patterns (Arrhythmia)
* Lowered pressure in heart chambers (Reduced atrial pressure)
* Accelerated heart rate (Ventricular Tachycardia)
* Rapid and erratic heartbeats (Ventricular Fibrillation)
* Early, unscheduled heartbeats (Multifocal Premature Ventricular Contractions)
* Heartbeats that come in pairs (Ventricular Bigeminy)
* Temporary halt in heart’s electrical activity (Asystole)
* Sudden stop in effective blood flow due to failure of the heart to contract effectively (Cardiac Arrest)
* Feeling of lightheadedness or imbalance (Dizziness)
* A feeling of being on the verge of fainting (Lightheadedness)
* A sickening feeling in the stomach (Nausea)
* Lack of strength or muscle power (Weakness)
Recognizing these symptoms early on and getting management for them is key. If left untreated, they could lead to serious health problems, or even be fatal in some cases.
What Else Should I Know About Oculocardiac Reflex?
Bradycardia, or a slower than normal heart rate, is the usual sign of something doctors call OCR. In some cases, OCR could lead to serious heart issues that could be life-threatening. It is fairly common for patients having eye surgeries to experience OCR, with rates of it happening at around 63-68%. For many patients, this isn’t a big problem, but for some it could result in harmful effects.
OCR can also cause problems not related to the heart such as low blood pressure, fainting, and problems with the stomach like feeling sick or throwing up. This could be due to nerves in our body that are responsible for heart, lung and stomach function. After strabismus surgery (a form of eye surgery), the rates of children feeling sick or vomiting can be as high as 85%. This makes it a major reason for hospital stays after day procedures.
To manage OCR, the most effective treatment is instantly removing whatever caused it in the first place. Easing pressure on the eye or eye socket can stop the reflex. Doctors need to take care after the cause has been removed, but removing the cause can sometimes be difficult, especially if it is the result of an accident. In these cases, doctors may need to use drugs to manage the OCR and keep a close eye on the heart.
Preventing OCR can be achieved by choosing the right anesthetic because some kinds can increase the risk of triggering OCR. Medications like atropine or glycopyrrolate, given through a vein, can lower the chances of experiencing OCR. Atropine works by blocking signals to certain heart receptors, which can increase heart rate and improve heart conduction, counteracting the slow heart rate caused by OCR.
Ketamine, another drug, could also counteract the nerve stimulation by improving the activity of the nervous system. In fact, ESPAHBODI et al. (2015) found ketamine to be more effective than atropine in reducing OCR. Some studies have associated ketamine with lower rates of post-operative nausea, vomiting, and restlessness.
Blocks, which involve the use of a local anesthetic to numb a region of the body, with xylocaine hydrochloride, may also reduce the chances of experiencing OCR. Combining these blocks with other agents like atropine, which are known to decrease OCR, may further lower the risk of activating OCR.
Medications like fentanyl, sufentanil, and remifentanil, often used for their immediate pain-relieving effects, could trigger OCR and cause a slow heart rate. While the effects of many anesthetic drugs on OCR have been studied, some needs more research. Pre-treatment medications such as atropine and blocks should be routinely used during eye procedures or when managing eye injuries to lessen the impact of OCR and protect patients.
