Context: sympathovagal imbalance (SI) is a common finding in diabetes and is considered to be a cardiovascular risk factor. No data are available on sympathovagal balance (SB) in acromegalic patients (ACRO).

Objective: to evaluate SB in ACRO.

Patients: 20 non-diabetic, non-hypopituitary acromegalic patients, 13 women and 7 men (mean age 51.30 ± 3.09 yr, mean ± SEM), compared with age-matched subjects (21 normal, 20 patients with type 1 diabetes mellitus, T1DM, and 15 patients with type 2 diabetes mellitus, T2DM).

Autonomic tests, used to evaluate SB, were performed by Power Spectral Analysis (PSA) of heart rate variability (HRV) in clinostatism (c) and orthostatism (o), using a frequency domain method. PSA identifies peaks of power: high frequency (HF), which expresses vagal activity, and low frequency (LF), which expresses sympathetic activity.

Results: ACRO displayed significantly lower LFc/HFc (P = 0.002) and LFo/HFo (P < 0.001) ratios than normal subjects. HFo was significantly higher in ACRO than in normal subjects (P < 0.001) and T1DM (P = 0.004), but no different from T2DM (P = 0.069). In untreated ACRO, the alterations found in the whole group were confirmed; no statistically significant differences were found between untreated ACRO and those treated with somatostatin analogs. Similarly, the same alterations found in the whole group were evident in the controlled ACRO, and no significant differences were found between controlled and uncontrolled patients.

Conclusion: our study evidenced a sympathovagal imbalance in acromegalic patients, which was due to vagal hypertone, was difficult to reverse and was not determined by medical therapy. This could be a new cardiovascular risk factor.