This original study gives us a possible new mechanism of how hypoglycemia can lead to cardiac conduction anomalies. Increased QT dynamicity and QTc prolongation was seen in 50% of patients with glucose levels < 70 mg/dL. QT dynamicity is well known to carry poor cardiac prognosis.
Of a concern, sulfonyluria caused hypoglycemia in one third of individuals with "well controlled" diabetes, most of whom were asymptomatic. Although further research is needed, these findings suggest avoidance of insulin injections or secretagogues, if feasible, to minimize hypoglycemic events.
Objective: To determine the effect of sulfonylurea-related hypoglycemia on cardiac repolarization and ectopy in the setting of well-controlled type 2 diabetes.
Research Design and Methods: 30 subjects with sulfonylurea-treated type 2 diabetes underwent 48 hours of concurrent continuous glucose monitoring and ambulatory electrocardiography. Ventricular repolarization (QTc) and QT dynamicity were analyzed during periods of hypoglycemia (<70 mg/dL for >20 min) and compared with periods of euglycemia and hyperglycemia combined. Cardiac ectopy rates during hypoglycemia were compared with ectopy rates when blood glucose was 70-180 mg/dL
Results: Mean HbA1c was 6.9%. Hypoglycemia was detected in 9/30 subjects (30%); episodes were typically nocturnal (67%) and asymptomatic (73%). Hypoglycemia-associated QTc prolongation was seen in 5/9 subjects with a large variation in individual response. Higher QT dynamicity, a poor prognostic factor in cardiac disease, was seen in subjects who experienced hypoglycemia compared with subjects who did not (0.193 vs. 0.159 for the nocturnal period; P = 0.01). This finding persisted after the hypoglycemic event.
The rates of ventricular and supraventricular ectopy demonstrated a nonsignificant trend toward an increase during hypoglycemia (median rate ratio 1.58 and 1.33, respectively). Similar, nonsignificant results were observed in a separate insulin-treated cohort.
Conclusions: Hypoglycemia, often unrecognized, is a frequent finding in well-controlled sulfonylurea-treated type 2 diabetes. It is associated with the novel finding of increased QT dynamicity and QTc prolongation in some individuals. Our findings suggest sulfonylurea-related hypoglycemia can have detrimental cardiovascular sequelae. Similar effects are also seen in the setting of insulin therapy.