Low glucose blood levels are associated with abnormal cardiac sympatho-vagal balance in type 2 diabetic patients with coronary artery disease

Background and Objectives: Glycemic control has been suggested to improve prognosis in diabetic patients, but recent trials failed to show benefits from intensive glycemic control. Hypoglycaemic episodes or large variability in glucose blood levels causing a sympatho-vagal imbalance of cardiac autonomic function (CAF) might play a role in this result. In our study we assessed whether blood glucose fluctuation may be related to variations in CAF during daily life in diabetic patients with coronary artery disease (CAD). Materials and Methods: Twelve patients with type 2 diabetes mellitus with CAD (65±4 years, 2 women) underwent simultaneous 48-hour ECG Hotter monitoring and continuous interstitial glucose measurements. The highest and lowest glucose levels for each 3-hour segments of the day were identified and heart rate variability (HRV) parameters were measured on Holter recordings on 5-minute intervals centred on these times. Results: Overall, 294 glucose levels were available for analysis. In the whole population several HRV indices were significantly lower in correspondence of the lowest glucose blood levels and this difference was much more evident in patients who were not taking beta-blockers, than in patients who were taking beta-blockers. A significant, although mild, correlation was found between glucose blood levels and several time-and frequency domain HRV variables in patients not taking beta-blockers, but not in these on beta-blockers therapy. Discussion: Our data suggest that, in type 2 diabetic patients with CAD, hypoglycaemic episodes are associated with depressed HRV and that beta-blocking agents are able to contrast this relation. These interesting results merit to be investigated in a larger population of patients.