The venous system is the main determinant of hypotension in patients with vasovagal syncope
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The venous system is the main determinant of hypotension in patients with vasovagal syncope
Giuseppe Fuc`a 2
Maurizio Dinelli 2
Paolo Suzzani 1
Salvatore Scarf`o 0
Fabio Tassinari 2
Paolo Alboni 2
0 Division of Cardiology, Ospedale del Delta , Lagosanto (Fe) , Italy
1 SEDA , Milano , Italy
2 Division of Cardiology, Ospedale Civile , 44042 Cento (Fe) , Italy
& The European Society of Cardiology 2006. All rights reserved. For Permissions, please e-mail:
eol>Syncope; Haemodynamics; Tilt test
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Aims In patients with vasovagal syncope (VVS), a neural reflex appears the main determinant of
hypotension leading to loss of consciousness; whether hypotension is mainly due to involvement of the
arterial system or the venous system remains a debated issue. The aim of the present study was to assess
which of these two systems is responsible for the fall in blood pressure (BP) in patients with VVS; to
this end, a haemodynamic study was carried out not only before and during loss of consciousness but
also during the recovery phase.
Methods and results Beat-to-beat recordings of heart rate (HR), BP (volume-clamp method) and stroke
volume (SV) (modelflow method), cardiac output (CO), and total peripheral resistance (TPR) were made
at rest, during unmedicated tilt testing (TT) and recovery from loss of consciousness in 18 patients with
a history of syncope (age 45 + 23 years) and positive response to TT. Blood pressure showed a significant
fall during prodromal symptoms and a further fall at the beginning of loss of consciousness, together
with a fall in SV, CO, and HR, and a slight, but significant, increase in TPR. At the beginning of recovery,
BP showed a significant increase and a further increase 5 min later, together with an increase in SV, CO,
and HR without significant changes in TPR.
Conclusion These results suggest that in VVS the fall in BP is mainly caused by reduced venous return to
the heart. The arterial system does not appear to be the main determinant of the fall of BP; however,
the system appears unable to make the appropriate compensatory changes.
Introduction
The haemodynamics of vasovagal syncope (VVS) should be
investigated during spontaneous episodes but, for obvious
reasons, adequate haemodynamic study is practically
impossible. Several observations suggest that the
hypotension and bradycardia induced by tilt testing (TT) are
similar to the spontaneous episodes,1–4 and tilt-induced
syncope is accepted as a model for this condition.5
It has been widely demonstrated that VVS is secondary to
a fall in blood pressure (BP), usually followed by bradycardia
due to withdrawal of sympathetic tone;6–11 however, the
genesis of VVS remains unclear. Blood pressure is dependent
on total peripheral resistance (TPR) and cardiac output
(CO); the latter on stroke volume (SV) and heart rate
(HR). In patients with normal hearts, without systolic
dysfunction, SV and CO are mainly determined by venous
return, whereas the arterial response is mainly manifest as
TPR. Certain data suggest that the fall in BP could be
related to an impairment of venous return due to
inadequate venoconstrictive response during orthostatic or
mental stress;11–19 other data suggest that the fall in BP
could be secondary to inadequate arterial vasoconstriction
during orthostatic or physical stress.20–25
The aim of the present study was to assess whether the
fall in BP responsible for the loss of consciousness is
mainly due to an inadequate compensatory response of
the venous system or the arterial system; to this end, a
haemodynamic study was carried out in patients with
tilt-induced syncope not only before and during loss of
consciousness but also during the recovery phase.
Methods
Patients referred for the evaluation of syncope were regarded as
candidates for the present study if they (i) were aged 18 years;
(ii) did not show any sign of cardiological or neurological disease,
or arterial hypertension; (iii) had negative carotid sinus massage
(not induction of syncope or presyncope during supine or standing
position); (iv) had syncope of unknown origin after the first
evaluation;26 (v) developed syncope associated with hypotension and/
or bradycardia after at least 5 min of unmedicated TT. We selected
this time to ensure that we could separate the haemodynamic
adjustments during the first 2 min of TT27 from those that occurred
during the minutes before loss of consciousness.
From January 2004 to March 2005, 181 patients underwent TT in
the out patient clinic and 22 met the eligibility criteria. The study
was approved by the Ethics Committee of Cento Hospital.
Tilt test protocol
The test was always performed in the morning in a quiet room
(temperature of 21–248C) after overnight fasting without any
medication. The procedure was carried out by means of an electronically
controlled tilt table with a footboard for weight-bearing. No patient
was taking cardioactive medication at the time of the study. After
15 min supine con (...truncated)