Background - The wide range of clinical presentation of orthostatic vasovagal syncope suggests different underlying changes in the cardiac autonomic modulation. Methods and Results - To evaluate the beat-by-beat modifications in the neural control of heart period preceding a syncopal event, we studied RR interval variability in 22 healthy subjects who experienced fainting for the first time during a 90°head-up tilt and in 22 control subjects by means of time-variant power spectral analysis. Sympathetic and vagal modulations to the sinoatrial node were assessed by the normalized power of the low-frequency (LF, ≃0.1-Hz) and high-frequency (HF, ≃0.25-Hz) oscillatory components of RR variability. When the patients were supine, no differences were observed in the hemodynamic and spectral parameters of the 2 groups. During the tilt procedure, RR, LF(NU), and HF(NU) (NU=normalized units) values were relatively stable in control subjects. During early tilt (T1), subjects with syncope had reduced RR intervals compared with control subjects. In 13 subjects with syncope, RR decreased while LF(NU) and LF/HF increased in the last minute of tilt before syncope (T2). Conversely, in the remaining 9 fainters, LF(NU) and LF/HF decreased from T1 to T2 and HF(NU) increased slightly. Conclusions - Two different patterns may be recognized in the cardiac autonomic changes preceding an occasional vasovagal event, namely, one characterized by a progressive increase of the marker of cardiac sympathetic modulation up to the onset of syncope, the other by a sympathetic inhibition with an impending vagal predominance. The recognition of different pathophysiological mechanisms in fainters may have important therapeutic implications.
|Number of pages||6|
|Publication status||Published - Oct 27 1998|
- Nervous system, autonomic
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine