MDUK-funded clinical research fellow, Dr Mark Hamilton, has found that a particular blood test might be useful for flagging potential heart issues in people with myotonic dystrophy type 1.
Background of the study
Checks of the heart form an important part of health screening for people with myotonic dystrophy. This is because the condition can affect the electrical system regulating the heartbeat, meaning some people eventually require a pacemaker device. Less commonly, myotonic dystrophy can also affect the mechanical ’pump’ of the heart; the heart muscle itself.
Doctors generally agree that at least an annual heart rhythm test (electrocardiography, or ‘ECG’) should be offered to everyone with myotonic dystrophy. It is less clear if and when additional tests such as an echocardiogram (looking at the heart muscle) should be recommended, and so practice may vary between different centres.
Cardiac troponin (cTnI) is a heart protein that leaks into the blood if the heart becomes damaged. The cTnI blood test is often carried out in hospital emergency departments for people with chest pain, as a very high level can suggest that a person is having a heart attack.
In this study, Dr Hamilton and colleagues investigated whether much smaller changes in cTnI levels can give useful information about the heart health of people with myotonic dystrophy attending an outpatient clinic.
What did the researchers do?
117 people with myotonic dystrophy type 1 participated while attending routine clinic appointments. All provided blood samples for genetic analysis, and for cTnI levels to be measured.
Relevant information was extracted from medical records, including ECGs, echocardiograms and muscle strength ratings. Further information was gathered for around two years after the blood samples were taken.
What did they find out?
cTnI levels were very variable among the 117 participants, including nine people with levels well above what is typically observed in the general population. These people were more likely to have heart muscle impairment than other participants.
Elevated cTnI levels did not help to distinguish people with significant abnormalities on their ECG. There was also no association between cTnI level and the size of the myotonic dystrophy gene expansion, nor measures of general muscle strength.
Approximately 53% of participants had a very low cTnI level. Among these, only one had any evidence of heart muscle impairment, which was mild. This suggests that a low level of cTnI may help to rule out significant heart muscle involvement.
How might this change care for people with myotonic dystrophy?
This was a relatively small, exploratory study, in which participants only underwent tests that were organised as part of their usual care (for example, only 53 had echocardiography). For these reasons, the study in itself does not provide enough evidence to change current practice.
However, it does suggest that blood biomarker tests, such as the cTnI test, maybe a useful addition to annual ECG screening for people with myotonic dystrophy. They could help to identify those who should have more detailed heart checks or closer follow-up.
The researchers hope that these findings will lead to larger studies exploring heart biomarkers in myotonic dystrophy, working towards a more harmonised approach to cardiac care.
The study was published in the scientific journal, PLOS ONE.
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