Sinus bradycardia 

Understanding bradycardia in spinal cord injury

Bradycardia is defined as a heart rate of less than 60 beats per minute (bpm). It is a common cardiovascular complication in people with cervical or high thoracic level spinal cord injuries.

Cardiac autonomic control

The heart is innervated by two components of the autonomic nervous system: the sympathetic nervous system and the parasympathetic nervous system.

The sympathetic nervous system (SNS) originates from spinal segments T1–T5 and functions to increase heart rate and contractility.

The parasympathetic nervous system (PNS) slows the heart rate and reduces contractility via the vagus nerve. The vagus nerve bypasses the spinal cord and remains intact following a spinal cord injury (SCI).

Causes

In the acute phase of SCI, particularly in cervical or high thoracic injuries, bradycardia may result from:

• Reduced sympathetic outflow, leading to a lower basal heart rate.
• Unopposed parasympathetic activity, which can further suppress heart rate.
• Neurogenic shock or spinal shock, where autonomic regulation is severely disrupted.

Bradycardia is most likely to occur within the first few weeks after injury, typically peaking around days 4–6 following a cervical SCI.

Additional parasympathetic stimulation—such as from endotracheal suctioning or vagal manoeuvres—can worsen bradycardia.

Management 

Check blood pressure to exclude asymptomatic autonomic dysreflexia.

Monitor heart rate and rhythm closely in patients with high-level SCI, especially in the acute phase.

Treatment considerations

Most treatments for sinus bradycardia are pharmacological or surgical in nature.  

However, evidence for pharmacological management in acute SCI is limited, and approaches should be guided by a specialist medical team.