Low Blood Sugar & Heartbeat in People With Diabetes
Study found abnormal rhythms when blood sugar dipped at night in people with type 2 disease
The study included 25 people with type 2 diabetes who had a known risk of heart disease. Their average age was 64 years. They were all being treated with insulin, and had been on insulin therapy for at least four years.
All of the study volunteers were monitored with a continuous glucose monitor for five days, as well as a 12-lead Holter monitor that captured heart activity. Both of these devices are portable, which allowed the study volunteers to carry on with normal daily activities.
Overall, the researchers recorded 1,258 hours of time with normal blood sugar levels, 65 hours with high blood sugar levels and 134 hours of low blood sugar levels. Low blood sugar was defined as a blood sugar of less than 63 milligrams per deciliter. These low blood sugar levels often went unrecognized, according to the study.
The risk of a slow heart rate was eight times higher when blood sugar was low at night compared to when it was normal. Slow heart rates didn't occur during the day, according to the study. Other types of abnormal heartbeats (arrhythmias) were also significantly higher at night when blood sugar was low compared to when blood sugar was normal. No irregular heartbeats occurred when low blood sugar symptoms were felt by the study participants.
"This study noted that spontaneous insulin-induced episodes of hypoglycemia were associated with asymptomatic mild heart arrhythmias. We have performed similar studies in animals, and noted similar arrhythmias during insulin-induced hypoglycemia," Fisher said.
"However, in animal studies, when blood sugar became severely low, more severe abnormal cardiac rhythms -- in other words, fatal heart rhythms -- were noted. So, based on existing animal and human data, we speculate that severe hypoglycemia-induced arrhythmias may contribute to sudden death in patients with insulin-treated diabetes," Fisher said.
He continued, "Nocturnal hypoglycemia is a major problem. People are less likely to wake up and treat their hypoglycemia at night. They're less likely to appreciate the normal warning symptoms of hypoglycemia because the entire sympathetic response is relatively blunted at night."
While the study found an association between low blood sugar levels and abnormal heart rhythms in people with type 2 diabetes, it did not prove a cause-and-effect relationship.
Another expert said the new findings highlight the dangers of hypoglycemia.
"This study suggests that the deeper the hypoglycemia, the more abnormal the heart rhythms. There seems to be some real scientific plausibility that recurrent episodes of hypoglycemia can cause abnormal disturbances of the heart. Each episode of hypoglycemia may have some element of risk," said Dr. John Anderson, the immediate past president of the American Diabetes Association.
"It may be that tight control of blood sugar might not be as important as safe control of blood sugar. Avoiding severe hypoglycemia should be a primary goal of therapy, especially for those who have a lot of risk for heart disease. That's why the American Diabetes Association said in 2012 that glycemic goals should be individualized. And, if you have to use insulin, avoiding those 3 a.m. hypoglycemias may be even more important," Anderson said.