Low prevalence of cardiac autonomic neuropathy in Type 1 diabetic patients without nephropathy

To assess the prevalence of cardiac autonomic neuropathy (CAN) in Type 1 diabetic patients with and without nephropathy.

Sixty-six consecutive patients without nephropathy (n = 24), with incipient (n = 26) or overt nephropathy (n = 16) and a diabetes duration between 21 and 31 years were examined. Heart rate variability (HRV) as measure for CAN was investigated with short-term spectral analysis in the low-frequency (LF) band (0.06-0.15 Hz), reflecting sympathetic and vagal activity, and high-frequency (HF) band (0.15-0.50 Hz), reflecting vagal activity. HRV was expressed as spectral power (ms2, log-transformed). Normal, age-corresponding reference values were established in 184 controls. QTc intervals and dispersion were measured.

After adjustment for age, there was no significant difference between healthy controls and patients without nephropathy. After further adjustment for diabetes duration, HbA1c, hypertension and treatment with beta-blockers, HRV in both frequency bands decreased with evidence of nephropathy. LF band (supine): patients without nephropathy 5.56 (4.89-6.21) (least squares means and 95% confidence interval (CI)), incipient nephropathy 5.72 (5.15-6.29) and overt nephropathy 4.11 (3.27-4.96). HF band (supine): without nephropathy 5.93 (5.26-6.60), incipient nephropathy 5.99 (5.41-6.57) and overt nephropathy 4.84 (4.00-5.68). Significant differences were found for patients without and with incipient nephropathy compared with those with overt nephropathy in the LF band and between patients with incipient nephropathy compared with those with overt nephropathy in the HF band. QTc intervals and QTc dispersion increased significantly with increasing nephropathy.

Long-term Type 1 diabetes without nephropathy was not associated with impaired cardiac autonomic function in our study. However, in those with nephropathy, a loss of both vagal and sympathetic activity was present, and the severity of CAN correlated positively with more advanced nephropathy.