Vasovagal syncope refers to a reflex response that, when triggered, gives rise to vasodilatation and bradycardia, although the contribution of both to systemic hypotension and cerebral hypoperfusion may differ considerably. It is valuable to assess the relative contribution of cardioinhibition and vasodepression before embarking on treatment as there are different therapeutic strategies for the two aspects. The triggering events might vary considerably over time in any individual patient. The ‘classical’ vasovagal syncope is mediated by emotional or orthostatic stress and can be diagnosed by history taking. ‘Non-classical’ presentations are frequent and these forms are diagnosed by minor clinical criteria, exclusion of other causes for syncope (absence of structural heart disease) and the positive response to tilt testing or carotid sinus massage. Examples of non-classical vasovagal syncope include episodes without clear triggering events or premonitory signs.
Criteria for selection of patients
In general, initial ‘treatment’ of all forms of neurally-mediated reflex syncope comprises reassurance on the begnin nature of the syndrome, education regarding avoidance of triggering events and predisposing factors, recognition of premonitory symptoms and maneuvers to abort the episode, the avoidance of volume depletion and prolonged upright posture. The above measures are sufficient for the vast majority of the patients affected by vasovagal syncope. Additional treatment may be necessary in high risk or high frequency settings which have been defined by the ESC Task force on Syncope (1) when:
- syncope is very frequent, e.g. alters the quality of life
- syncope is recurrent and unpredictable (absence of premonitory symptoms) and exposes patients at “high risk” of trauma
- syncope occurs during the prosecution of a ‘high risk’ activity (e.g., driving, machine operator, flying, competitive athletics, etc)
Among those settings, cardiac pacing may be reserved to those patients with cardioinhibitory vasovagal syncope with a frequency >5 attacks per year or severe physical injury or accident and age >40 (1) In order to limit the vasodepressor component of the vasovagal reflex, dual-chamber pacemaker with rate-hysteresis features are usually preferred even though formal comparison studies among modes of pacing have not yet been performed.
Knowledge from randomised controlled trial
Pacing for vasovagal syncope has been the subject of five major multicentre randomised controlled trials (2,3,4,5,6): three gave positive and two gave negative results. Putting together the results of the 5 trials, 318 patients were evaluated; syncope recurred in 21% (33/156) of the paced patients and in 44% (72/162) of not paced patients (p<0.000). However, all the studies have weaknesses and further follow-up studies addressing many of these limitations (particularly the pre-implant selection criteria of the patients who might benefit from pacemaker therapy) need to be completed before pacing can considered an established therapy.
It seems that pacing therapy might be effective in some but not in all patients. This is not surprising if we consider that pacing is probably efficacious for asystolic reflex but has no role in combating hypotension which is frequently the dominant reflex in vasovagal syncope. How to stratify the patients is still uncertain. A recent study using the Implantable Loop Recorder as reference standard (7) showed that only about half of the patients had an asystolic pause recorded at the time of spontaneous syncope which might eventually benefit from a pacemaker. In the other patients a pacemaker is unlikely to be effective. The role of the Implantable Loop Recorder for selecting patients who may benefit from cardiac pacing is actually under evaluation.
A widely used method for selecting patients candidates to cardiac pacing is the finding of a cardioinhibitory form during tilt testing. Nevertheless, recent data showed that the mechanism of tilt-induced syncope was frequently different from that of the spontaneous syncope recorded with the Implantable Loop Recorder (7). These data show that the use of tilt testing for assessing the effectiveness of different treatments has important limitations and its use is now disregarded in the ESC Guidelines (1).
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.