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From the Centro Ricerche Cardiovascolari, CNR; Medicina Interna II e
Medicina Interna III (S.P.), Ospedale L. Sacco, Università di Milano;
Divisione di Cardiologia (S.D.), Ospedale Uboldo, Cernusco S/N; Medicina del
Lavoro (F.B.), Ospedale di Novara; and Dipartimento di Bioingegneria (A.B.,
L.M., S.C.), Politecnico di Milano, Milano, Italy.
Correspondence to Dr Raffaello Furlan, Medicina Interna II, Ospedale L. Sacco, Università di Milano, Via G.B. Grassi, 74, 20157 Milano, Italy. E-mail r.furlan{at}planet.it
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,
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.
© 1998 American Heart Association, Inc.
Clinical Investigation and Reports
Cardiac Autonomic Patterns Preceding Occasional Vasovagal Reactions in Healthy Humans
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,
LFNU, and HFNU (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 LFNU and LF/HF increased in the last minute
of tilt before syncope (T2). Conversely, in the remaining 9
fainters, LFNU and LF/HF decreased from T1 to
T2 and HFNU increased slightly.
Key Words: syncope • nervous system, autonomic • spectroscopy
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