Insulin therapy improves cardiac autonomic function in type 2 diabetic patients

Background and Aim: There is scintigraphic evidence that insulin improves cardiac autonomic innervation in diabetic patients. The aim of the study was to assess the effects of insulin therapy on parameters of cardiac reflex tests in type 2 diabetic patients. Patients and Methods: 30 type 2 diabetic patients with an HbA(1c) of > 7.5% under oral antidiabetic agents were included into the 4-month follow-up. Insulin therapy was performed according to standardized clinical guidelines. Parameters of five cardiac reflex tests were assessed to study cardiac autonomic function: Coefficient of variation (CV) of heart rate variation (HRV) at rest and during deep breathing, HRV in response to standing (max./min. 30:15-ratio), Valsalva ratio, systolic blood pressure response (> 1 test abnormal = cardiac autonomic neuropathy [CAN]). QT(QTc)-interval was also assessed in the patients. Results: At 4-months follow-up, mean insulin dosage in the patients was 25 +/- 8 IU/day. HbA(1c) was decreased from 9.2 +/- 0.7 to 7.2 +/- 0.6 % (p < 0.001). Three parameters of cardiac autonomic function were significantly improved: CV of HRV at rest 2.79 +/- 0.84 versus 2.96 +/- 0.85 (P < 0,001), CV of HRV during deep breathing 4.15 +/- 1.46 versus 4.38 +/- 1.68 (P = 0.002), 30:15 ratio 1.06 +/- 0.05 versus 1.09 +/- 0.04 (P < 0.05). Length of QTc-interval changed significantly from 417 +/- 12 ms at month 0 to 398 +/- 11 ms at month 4 (P < 0.05). Conclusions: The study demonstrates that insulin therapy with regular insulin optimizes cardiac autonomic function in type 2 diabetes mellitus. It emphasizes the value of cardiac reflex tests with regrad to follow-up of cardiac autonomic function in diabetes.