vasovagal syncope

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Related to Vasovagal reflex: vasovagal syncope, Vagovagal reflex

syncope

 [sing´kah-pe]
faint. adj. adj syn´copal, syncop´ic.
cardiac syncope sudden loss of consciousness, either with momentary premonitory symptoms or without warning, due to cerebral anemia caused by ventricular asystole, extreme bradycardia, or ventricular fibrillation.
laryngeal syncope tussive syncope.
neurocardiogenic syncope a particularly serious type of vasovagal attack; the etiology is unknown.
stretching syncope syncope associated with stretching the arms upward with the spine extended.
swallow syncope syncope associated with swallowing, a disorder of atrioventricular conduction mediated by the vagus nerve.
tussive syncope brief loss of consciousness associated with paroxysms of coughing.
vasovagal syncope vasovagal attack.

va·so·de·pres·sor syn·co·pe

faintness or loss of consciousness due to reflex reduction in blood pressure.
Synonym(s): vasovagal syncope

neurocardiogenic syncope

A syncope with a psychogenic substrate and predisposition to bradycardia, hypotension and peripheral vasodilation.
 
Clinical findings
Abrupt loss of vascular tone; nausea; diaphoresis; pallor.
 
Diagnosis
Tilt test, in which the patient is placed on a tilt table at a 40º to 80º angle from horizontal and maintained in a motionless upright position for 10–15 minutes or more.
 
Management
Beta blockers—e.g., metoprolol, theophylline, disopyramide.

Mechanism
Uncertain; probably activation of myocardial mechanoreceptors (C fibres), with decreased efferent sympathetic tone and increased efferent parasympathetic tone.

vasovagal syncope

Neurocardiogenic syncope, see there.

va·so·va·gal syn·co·pe

(vā'sō-vā'găl sing'kŏ-pē)
Faintness or loss of consciousness due to increased vagus nerve (parasympathetic) activity.
Synonym(s): vasodepressor syncope.

vasovagal syncope

See FAINTING.
References in periodicals archive ?
For needle phobics with the tendency to the vasovagal reflex reaction or with hypersensitivity to pain, Emanuelson recommends Eutectic Mixture of Local Anesthetics or EMLA cream (a prescription topical anesthetic cream).
The vasovagal reflex in needle phobia may include virtually any type and combination of autonomic symptoms, eg, a clammy diaphoresis, pallor, nausea, respiratory disturbances, and various levels of unresponsiveness.(1)(4)(30)(37)(38)(39)(40) Although the onset of the vasovagal reflex from the start of a needlestick is often immediate, ie, within 2 to 3 seconds, a prospective study of 84 blood donors who fainted found that 16.7% experienced syncope from 5 to 30 minutes after phlebotomy.(38) Another series of 64 blood donors who fainted found that 14% fainted after leaving the phlebotomy site and returning to work, sometimes several hours later.(39)
In several case reports, ECG changes during the vasovagal reflex among patients with needle phobia have included sinus arrhythmia, premature atrial contractions, premature junctional contractions, unifocal and multifocal premature ventricular contractions, bigeminy, first- and second-degree block, changes in P waves, ST waves, and T waves, sinus bradycardia, sinus tachycardia, ventricular tachycardia, ventricular fibrillation, and asystole.(1)(2)(5)(26)(27)(28)(37) Presumably, these ECG changes are secondary to vagal influence on the sinoatrial and atrioventricular nodes, and perhaps also to the antagonism between the activated sympathetic and parasympathetic systems on the heart.(27)
Probably because the pituitary perceives a reduced intravascular volume during vasovagal shock, vasopressin or antidiuretic hormone (ADH) rises in the vasovagal reflex with venipuncture,(1)(2)(45) as does endothelin.(45) Renin also increased by 200% in one patient with needle phobia,(46) but aldosterone and angiotensin levels have not yet been tested in needle phobic patients.
Both the vasovagal reflex and needle phobia strongly tend to run in families.(1)(2)(7)(47)(48)(49) The heritability of blood-injury phobia in twin studies, including fear of injections, wounds, blood, and pain, has been estimated to be 48%.(50) Variations in PR, QRS, and QT intervals and heart rate have heritabilities of 30% to 60%,(51) and the autonomic control of the cardiovascular system in general, based on twin comparisons, is probably genetically influenced.(52) Therefore, the plunges in blood pressure and pulse and the ECG anomalies during a needle-phobic response are surely also genetically influenced.
A vasovagal reflex has been found in all patients with needle phobia tested so far, and the medical histories of most of them include an adverse learning experience that triggered the needle fear.(47) Therefore, a reasonable theoretical model might propose that needle phobia depends both on an inherited reflex that is hard-wired in neurocardiovascular and neuroendocrine pathways and on the learning of a conscious fear.
Blood-injury phobia, which is often linked with needle phobia,(3) probably often arises when a patient with a strong vasovagal reflex undergoes a needle procedure or has an accident that results in a vasovagal response.
Over the 4+ million years of human evolution, surely many genes controlling blood pressure, pulse, cardiac rhythm, and stress hormone release were selected for to create the vasovagal reflex.