Sympathovagal imbalance in acromegalic patients.

CONTEXT: Sympathovagal imbalance 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.
OBJECTIVE: The objective of this study was to evaluate SB in acromegalic patients. PATIENTS: Twenty nondiabetic, nonhypopituitary, acromegalic patients (13 women and seven men; mean age +/- sem, 51.30 +/- 3.09 yr) were compared with age-matched subjects (21 normal subjects, 20 patients with type 1 diabetes mellitus, and 15 patients with type 2 diabetes mellitus).
INTERVENTIONS: Autonomic tests, used to evaluate SB, were performed by power spectral analysis of heart rate variability in clinostatism (c) and orthostatism (o), using a frequency domain method. Power spectral analysis identifies peaks of power: high frequency (HF), which expresses vagal activity, and low frequency (LF), which expresses sympathetic activity.
RESULTS: Acromegalic patients displayed significantly lower LFc/HFc (P = 0.002) and LFo/HFo (P < 0.001) ratios than normal subjects. HFo was significantly higher in acromegalic patients than in normal subjects (P < 0.001) and patients with type 1 diabetes mellitus (P = 0.004), but no different from that in type 2 diabetes mellitus patients (P = 0.069). In untreated acromegalic patients, the alterations found in the whole group were confirmed; no statistically significant differences were found between untreated acromegalic patients and those treated with somatostatin analogs. Similarly, the same alterations found in the whole group were evident in the controlled acromegalic patients, and no significant differences were found between controlled and uncontrolled patients.
CONCLUSION: Our study evidenced that sympathovagal imbalance in acromegalic patients, due to vagal hypertone, is difficult to reverse and is not influenced by medical therapy. This could be a new cardiovascular risk factor.