Bradycardia is when your heart rate beats less than 60 times a minute.
To put this into perspective, 60-100 beats per minute is considered a normal range.
While a resting heart rate below 60 in athletes is often an indicator of efficient heart health, it can also be a serious condition that requires medical attention (especially after a spinal cord injury).
Bradycardia is very common after spinal cord injury, especially in higher-level (T6 and up) injuries.
To help you understand the link between spinal cord injury and heart rate, this article will go over the causes, symptoms, and management for bradycardia after SCI.
Spinal Cord Injury and Bradycardia
Your autonomic nervous system is responsible for regulating body functions that you don’t have conscious control over like heart rate, temperature regulation, digestion, and blood pressure.
It consists of the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system regulates your ‘fight or flight’ response. This is activated in times of stress. Your alertness, heart rate, and blood pressure increase.
In contrast, the parasympathetic nervous system regulates your ‘rest and digest’ response. When stimulated, your heart rate and blood vessels relax.
Sympathetic fibers that regulate your heart rate are located around the T1-T5 segments of the spinal cord. Therefore, higher-level spinal cord injuries will disrupt sympathetic influence over heart rate.
Parasympathetic fibers branch off from the brain stem with the vagus nerve and are unaffected by spinal cord injury.
This results in an imbalance where parasympathetic tone is left unopposed, causing bradycardia.
Signs of Bradycardia After Spinal Cord Injury
Symptoms of bradycardia include:
- Shortness of breath
These symptoms occur because the heart is unable to efficiently pump blood throughout the body.
Blood is rich in oxygen and other nutrients that are essential to fuel cellular activity and keep our bodies running.
Without a sufficient supply of blood, our bodies start to feel weak and cannot function optimally.
Unopposed parasympathetic tone due to loss of sympathetic tone after spinal cord injury can cause neurogenic shock.
During neurogenic shock, heart rate slows and blood vessels expand (vasodilation).
This causes blood to pool in the arms and legs rather than return to the heart.
Neurogenic shock is a serious medical condition that can cause your major organ systems to dysfunction due to poor circulation.
Bradycardia also occurs during autonomic dysreflexia.
Autonomic dysreflexia is when the body overreacts when stimulated below your level of injury.
After a spinal cord injury, you may lose sensation below your level of injury. Think of autonomic dysreflexia as your body’s way of letting you know that something isn’t right.
Common triggers of autonomic dysfunction include:
- Tight clothes
- Extreme temperatures
- Full bladder
- Skin irritations
When stimulated, your sympathetic reflexes will react and tighten blood vessels. As a result, the baroreceptors (nerves that relay information about blood pressure to the brain) tell the brain to send out signals to relax the blood vessels.
However, these brain signals cannot get past the site of injury and only affects the body above your level of injury. This leads to hypertension (high blood pressure) below your level of injury, vasodilation above your level of injury, and bradycardia.
This imbalance can cause you to experience headaches, feelings of anxiety, and warmer temperatures above your level of injury.
Managing Bradycardia After Spinal Cord Injury
Treatments for bradycardia focus on promoting a normal heart rate.
Generally, atropine will be used to reduce vagus nerve activity on the heart, allowing heart rate to increase.
Other treatments for bradycardia include the use of IV fluids to increase volume in the blood vessels and the use of vasopressors like norepinephrine and dopamine.
Vasopressors make the blood vessels tighten to increase heart rate and blood pressure.
This prevents blood from pooling in the arms and legs and promotes stable circulation.
Living With Bradycardia After Spinal Cord Injury
If you’re experiencing weakness, dizziness, or sluggishness, it may be caused by a slow heart rate.
While bradycardia is most common in the first 2-6 weeks following a spinal cord injury, secondary complications like autonomic dysreflexia can also cause your heart rate to slow down.
A decreased heart rate can be a sign that your heart is unable to efficiently pump blood throughout your body, which can affect overall organ functioning and health.
Hopefully, this article helped you better understand how bradycardia can affect your day-to-day life after spinal cord injury.
There are many risks associated with bradycardia after spinal cord injury, so be sure to seek medical assistance and get the treatment you need to optimize your health.
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