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Cardiac Autonomic Nervous Dysfunction and Glycemic Control

Older individuals are at an increased risk for cardiac autonomic nervous dysfunction…

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Cardiac autonomic nervous dysfunction (CAND) is an early subclinical complication of type 1 diabetes. It is also known to be associated with microalbuminuria both in adults and adolescents and with the progression of renal disease in adults. CAND raises the risk of mortality, but the glycemic threshold at which it develops is not quite clear.

Researchers from the German Diabetes Center at Heinrich Heine University, Düsseldorf, Germany examined the prevalence of, risk factors for, and impact of CAND in glucose intolerance and diabetic patients.

A population-based cross-sectional study known as the KORA S4 survey was used, of which there were 1,332 eligible participants between 55 and 74 years of age. After 130 participants who had known diabetes mellitus were excluded, there was a remainder of 1,202 that underwent an OGTT. Other observations were heart rate variability (HRV) and QT variability which were computed from supine 5 min ECGs.

After all data was collected and recorded, 565 participants had normal glucose tolerance (NGT), 336 had isolated impaired fasting glucose (i-IFG), 72 had isolated impaired glucose tolerance (i-IGT), 151 had combined IFG-IGT (IFG-IGT) and 78 had newly detected diabetes mellitus (n-DM). Adjusted normal HRV limits were defined in the NGT population (5th and 95th percentiles). Throughout the study three HRV measures were more frequently abnormal in those with known diabetes mellitus, newly detected diabetes mellitus, impaired fasting glucose-impaired glucose tolerance and isolated impaired fasting glucose than in those with normal glucose tolerance (p < 0.05). The rates of CAND (≥2 of 4 HRV indices abnormal) were shown to be: NGT, 4.5%; i-IFG, 8.1%; i-IGT, 5.9%; IFG-IGT, 11.4%; n-DM, 11.7%; and k-DM, 17.5% (p < 0.05 vs NGT, except for i-IGT). In this study, a reduced HRV was associated with cardiovascular risk factors which was used to construct a screening score for CAND. Results showed that mortality was higher in participants with reduced HRV (p < 0.05 vs normal HRV).

The researchers concluded that in the general population between 55 and 74 years of age, the prevalence of CAND is increased not only in individuals with diabetes, but also in those with impaired fasting glucose-impaired glucose tolerance and, to a smaller extent, in those with isolated impaired fasting glucose. CAND was associated with mortality and modifiable cardiovascular risk factors which could be used to screen for reduced heart rate variability in clinical practice.

Practice Pearls:

  • Overall, three abnormal measures of heart rate variability occurred more frequently in patients with known and newly diagnosed diabetes, IFG-IGT, and isolated IFG compared with those with normal glucose tolerance.
  • The rates of CAND were significantly higher in all groups compared with rates of normal glucose tolerance with the exception of isolated IGT.
  • Patients with reduced heart rate variability had significantly higher mortality than those with normal heart rate variability.

D Ziegler, A Voss, W Rathmann, et al. "Increased Prevalence of Cardiac Autonomic Dysfunction at Different Degrees of Glucose Intolerance in the General Population: The KORA S4 Survey". Diabetologia 2015 Feb 28;[EPub Ahead of Print]