The venous system is the main determinant of hypotension in patients with vasovagal syncope

EP Europace, Oct 2006

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.

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The venous system is the main determinant of hypotension in patients with vasovagal syncope

Europace 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 - 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)


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Fucà, Giuseppe, Dinelli, Maurizio, Suzzani, Paolo, Scarfò, Salvatore, Tassinari, Fabio, Alboni, Paolo. The venous system is the main determinant of hypotension in patients with vasovagal syncope, EP Europace, 2006, pp. 839-845, Volume 8, Issue 10, DOI: 10.1093/europace/eul095