Spinal cord injuries (SCIs) directly affect the heart, but the extent of any damage done is reliant on the severity of an SCI, new research out of the University of British Columbia, Canada, states.

In a study published this week in Experimental Physiology, first author and graduate student Jordan W. Squair and colleagues wrote SCIs can have a significant impact on a patient’s heart health, depending on the extent of their injury. While the heart undergoes inevitable change following an SCI, only a small number of preserved nerve fibers are necessary for it to function normally.

However, following a primary SCI injury patients often experience an exacerbation of that initial trauma known as a “secondary injury.” Complex cellular processes dictate the spread of this injury, Squair et al. wrote, but a secondary injury can result in growth and spreading of the first SCI—growth that can reach a patient’s heart.

The researchers used rodent models to compare different severities of SCIs. Since it’s impossible to mimic the symptoms of a spinal cord injury and its implications on the heart in a human patient, Squair and his team mirrored those symptoms in clinically-relevant rodent models where they could carefully control the amount of damage to the spinal cord, as well as definitively assess heart function after an injury.

According to the study, Squair et al. tested three different severities of T3 spinal cord contusions—MODERATE, 200Kdyn contusions, SEVERE, 400kdyn contusions and SHAM—and combined both standard echocardiography and speckle tracking analyses to investigate in vivo cardiac function and deformation after experimental SCI in rat models.

They found that SEVERE SCI induced a decline in left-ventricular chamber size in the rats, as well as a reduction in in vivo left ventricular deformation throughout the systolic portion of the cardiac cycle. This severity also caused structural changes in cardiomyocytes, the researchers reported, including decreased length and width and an increase in the length/width ratio.

“This is the first study to demonstrate that the severity of SCI determines the course of changes to the intrinsic structure of cardiomyocytes, which are directly related to contractile function of the LV,” Squair and colleagues wrote.

MODERATE SCI-simulated rats saw no changes in any metric vs. those with SHAM, the authors wrote.

Squair and co-authors said their findings could have important clinical implications—namely the fact that they now know heart injury could be spared or downsized if doctors are able to preserve more nerve fibers following an SCI. Just these simple steps, the authors wrote, could result in huge improvements in heart function for spinal cord injury patients who are already at a higher risk for heart disease than those who haven’t experienced an SCI.