Abstract 16079: Association between Impaired Cardiovascular Autonomic Function and Hypoglycemia in Patients with Type 1 Diabetes Mellitus

Abstract

Background and Purpose - Cardiac autonomic neuropathy (CAN), which can be documented by impaired heart rate variability (HRV), is an independent predictor of CVD mortality. In type 1 diabetes (T1DM) the sympathetic/parasympathetic imbalance associated with CAN may increase the risk of arrhythmia during hypoglycemia, with higher risk of sudden death. We evaluated the associations between hypoglycemia (blood glucose < 70 mg/dl), fluctuations between hypo and hyperglycemia (blood glucose > 200 mg/dl), and CAN in patients with T1DM.

Methods - CAN was assessed by standardized cardiovascular reflex testing (CARTs) (paced deep breathing, Valsalva maneuver and postural changes) and by HRV in 26 patients with T1DM and no evidence of ischemic heart disease. Indices of HRV: low frequency (LF) power, high frequency (HF) power and LF/HF at rest and during CARTs were analyzed with the ANX 3.1 (ANSAR Inc, PA) with adjustments for age and sex. Continuous blood glucose recordings were obtained at 5-minute intervals over a period of five days in all patients with the iPro CGM System (Medtronic, Northridge CA). Time spent in hypo and hyperglycemia and associations with CAN were analyzed by Spearman correlations and Wilcoxon rank sum test.

Results - The mean age of the subjects was 29 ±11 years, the mean duration of diabetes was 12 ±4 years, and none were on beta-blockers. The mean hemoglobin A1c was 8.3 ±1.3%; mean systolic blood pressure was 114 ±11 mmHg; mean diastolic blood pressure was 73 ±8 mmHg; and mean LDL cholesterol was 93 ±26 mg/dl. In preliminary analyses, we found a negative correlation between hyperglycemia and R-R variation during deep breathing (P = 0.0166). There was a positive correlation between hypoglycemia and the LF/HF during deep breathing (P = 0.0236), while a negative correlation was seen between hypoglycemia and Valsalva ratio (P = 0.0186).

Conclusions - In this cohort of T1DM patients, a higher incidence of hypoglycemia was associated with indices of HRV and R-R response during deep breathing suggesting parasympathetic/sympathetic imbalance. Prospective studies are ongoing in these patients.