Effect of hypoglycemia on measures of myocardial blood flow and myocardial injury in adults with and without type 1 diabetes: a prospective, randomized, open-label, blinded endpoint, cross-over study

Aims: Hypoglycemia provokes a profound autonomic response in humans including cardiovascular effects. This study examined the effect of experimentally-induced hypoglycemia on measures of myocardial blood flow and myocardial injury in adults with, and without, type 1 diabetes.Methods and Results: In a prospective, randomized, open-label, blinded, endpoint cross-over study, 17 young adults with type 1 diabetes with no cardiovascular risk factors, and 10 healthy non-diabetic volunteers, underwent hyperinsulinemic euglycemic (blood glucose 4.5-5.5 mmol/L) and hypoglycemic (2.2-2.5 mmol/L) clamps. Myocardial blood flow was assessed using transthoracic echocardiography Doppler coronary flow reserve (CFR) and myocardial injury using plasma high-sensitivity cardiac troponin I (hs-cTnI) concentration.During euglycemia, a non-significant trend for lower CFR was observed in participants with type 1 diabetes than in those without type 1 diabetes (3.66±0.47 versus 3.92±0.85), and a non-significant lower trend also occurred during hypoglycemia (type 1 diabetes: 3.54±0.58 versus non-diabetes: 3.80±0.84). A generalized linear mixed-model analysis was performed, with diabetes status and euglycemia or hypoglycemia as factors affecting CFR. No significant statistical difference in CFR was observed for diabetes status (p=0.23) or between euglycemia and hypoglycemia (p=0.31). No changes in hs-cTnI occurred during hypoglycemia or in the recovery period (p=0.86).Conclusions: While the observed reduction in coronary flow reserve did not achieve significance during exposure to insulin-induced hypoglycemia in healthy young men with type 1 diabetes, with no evidence of myocardial injury, adverse cardiovascular effects of hypoglycemia cannot be excluded in older people who have coronary disease. Further studies are required to investigate this putative problem.