XXXX . Role of sympathovagal balance.

@entity1 @entity1169 @entity308 @entity591 @entity1817 @entity56 @entity3897 @entity3044 @entity7129
BACKGROUND: "Inappropriate" @entity7129 (IST) is an uncommon and poorly defined @entity591 characterized by inappropriate @entity591 and exaggerated acceleration of heart rate with "normal" P wave. The mechanism of this @entity591 is unknown. The purpose of the present study was to determine the role of autonomic balance in the genesis of IST. METHODS AND RESULTS: Six female @entity1 aged 23 to 38 years with IST and 10 age- and sex-matched control subjects were assessed with the following autonomic function tests: (1) sympathovagal balance to the sinus node assessed by calculating the LF/HF (low frequency/high frequency) ratio using power spectral analysis both in the supine position and after 10 minutes of head-up tilt to 60 degrees, (2) cardiovagal reflex assessed by cold face test (CFT), (3) beta-adrenergic sensitivity as determined by calculating @entity3044 dose-response curves and @entity3044 chronotropic dose 25 (CD25), and (4) intrinsic heart rate (IHR) assessed after autonomic blockade with @entity3897 0.04 mg/kg and @entity1169 0.2 mg/kg administered as an intravenous bolus. No significant differences in the LF/HF ratio both in the supine position (2.8 +/- 0.3 versus 2.6 +/- 0.4) and during upright tilt (8.7 +/- 1.3 versus 8.5 +/- 0.5) were observed between control subjects and IST @entity1 . Cardiovagal response to CFT was markedly @entity308 in all @entity1 (6.3% IST @entity1 versus 24.2% control subjects, P < .001). beta-Adrenergic @entity56 to @entity3044 was noted in all @entity1 (mean CD25, 0.29 +/- 0.10 microgram IST @entity1 versus 1.27 +/- 0.4 microgram control subjects; P < .001), and high IHR was noted in all cases. The @entity1 were treated with high doses of beta-blockers with adequate short-term control. Radiofrequency catheter ablation of the sinus node area was performed in one drug-refractory @entity1 . CONCLUSIONS: These findings suggest that the mechanism leading to IST is related to a primary @entity1817 characterized by a high IHR, @entity308 efferent cardiovagal reflex, and beta-adrenergic @entity56 .
