Increased QT dynamicity during hypoglycemia cause for concern
medwireNews: Hypoglycemia is associated with increased nocturnal QT dynamicity in patients with well-controlled sulfonylurea-treated type 2 diabetes, Australian researchers report.
They say that this finding “is concerning in light of previously reported associations of increased QT dynamicity with increased mortality” and therefore warrants further investigation.
Timothy Middleton and colleagues from the Royal Prince Alfred Hospital in Sydney, New South Wales, also found that hypoglycemia was associated with QTc prolongation – a measure of delayed ventricular repolarization – in some participants.
Their study included 30 individuals with sulfonylurea-treated type 2 diabetes who underwent 48 hours of concurrent continuous glucose monitoring and ambulatory electrocardiography.
Although diabetes was well controlled, with a mean glycated hemoglobin (HbA1c) of 6.9% (52 mmol/mol), nine (30%) participants experienced hypoglycemic episodes (HbA1c <3.5 mmol/L for >20 min). These episodes were typically asymptomatic (73%), occurred at night (67%), and ranged from 20 minutes to more than 8 hours in duration.
Five of the nine patients with hypoglycemia experienced QTc prolongation, and there were large variations in individual response, which could not be explained by either the duration or the depth of hypoglycemia, the researchers note.
In addition, nocturnal QT dynamicity was significantly higher among individuals who experienced hypoglycemia compared with those who did not, at 0.193 versus 0.159. Daytime QT dynamicity was higher in the hypoglycemic group, but not significantly so.
Middleton and co-researchers also looked at cardiac ectopy rates and found a trend toward increased ventricular and supraventricular ectopy during hypoglycemia versus euglycemia (HbA1c 4–10 mmol/L).
“Collectively, the results observed in our study of sulfonylurea-treated subjects suggest an association between hypoglycemia and abnormal ventricular repolarization,” the researchers write in Diabetes Care.
To determine whether their findings apply to hypoglycemia per se or more specifically to sulfonylurea-related hypoglycemia, they assessed raw data from a similar study that included 14 insulin-treated individuals.
The findings were comparable to the current study and therefore suggest “an association with iatrogenic hypoglycemia rather than sulfonylurea treatment specifically,” Middleton et al remark.
They conclude that although their findings are “concerning,” the small sample size means that larger, more detailed studies with longitudinal follow-up are needed “to further determine the strength and temporal association of hypoglycemia propensity with QT dynamicity.”
By Laura Cowen
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