Simple syncope

Introduction Simple syncope, also known as vasopressive syncope, vasovagal syncope. This is the most common type of syncope, accounting for about 90% of all syncope. There are often obvious incentives, such as nervousness, fear, anxiety, pain, seeing bleeding, and hearing bad news. Often occurring in frail young women.

Cause

Although Lewis has been diagnosed with vasovagal syncope for nearly 70 years, the etiology and pathogenesis of this disease have not yet been fully elucidated. At present, most scholars believe that the basic pathophysiological mechanism is that the compensatory reflex of the autonomic nervous system of the child is inhibited, and the cardiovascular compensatory response cannot be maintained for the long straight stereo position. When a normal person stands upright, due to the effect of gravity, blood collects in the lower part of the limb, the blood in the head and chest is reduced, the venous return is reduced, the ventricular filling and the baroreceptors located in the ventricle are unloaded, and the brain stem is introduced into the brainstem trunk. Impulsive reduction, reflexively causes increased sympathetic excitability and decreased parasympathetic activity. It usually manifests as an increase in heart rate, a slight decrease in systolic blood pressure and an increase in diastolic blood pressure. Children with vasovagal syncope cannot maintain a compensatory cardiovascular response to long straight steric positions. Studies have reported that vasospasm levels and cardiac adrenergic nerve tensions in circulating blood of patients with vasovagal syncope continue to increase, leading to a high contraction of ventricle relative emptying, which in turn stimulates mechanoreceptors of the posterior wall of the left ventricle (unmyelinated) C nerve fibers), causing a sudden increase in vagal impulses to the brainstem, inducing reflex bradycardia and peripheral vasodilation as opposed to normal people, leading to severe hypotension and bradycardia, causing cerebral hypoperfusion, cerebral hypoxia And fainting.

In addition, studies have also found that neuroendocrine regulation is also involved in the pathogenesis of vasovagal syncope, including renin-angiotensin-aldosterone system, catecholamines, serotonin, endorphin and nitric oxide, but its exact The mechanism is still unclear.

an examination

Related inspection

Blood pressure electrocardiogram cerebrospinal fluid glucose and serum glucose ratio human body weight balance instrument upright tilt test

The diagnosis of neurovascular-mediated vasovagal syncope has long been indirect, time consuming, and expensive, and often has no clear results.

The head-up tilt test (HUT) is a new type of examination method developed in recent years, which plays a decisive role in the diagnosis of vasovagal syncope. The positive reaction was that the sick child had a syncope with a significant decrease in blood pressure or a decrease in heart rate after the patient was tilted from the supine position.

The diagnostic mechanism of the erect tilt test for vasovagal syncope is not fully understood. When the normal person is in the upright tilt position, the ventricular filling is insufficient, the effective stroke volume is reduced, the inhibitory impulse of the arterial sinus and the aortic arch baroreceptor afferent vasomotor center is weakened, and the sympathetic tone is increased, causing the heart rate to increase. Keep blood pressure at a normal level. In children with vasovagal syncope, this autonomic compensatory reflex is suppressed, unable to maintain normal heart rate and blood pressure, plus decreased ventricular volume and increased sympathetic tone in the erect tilt position, especially in the presence of isoproterenol When the positive inotropic force acts, the ventricular contraction is insufficiently enhanced. At this time, the receptors in the posterior wall of the left ventricle are stimulated, the afferent fibers of the vagus nerve are activated, and the afferent center of the impulse is induced, causing central inhibition of the vasoconstriction. Excitement leads to bradycardia and/or decreased blood pressure, which reduces cerebral blood flow and causes syncope. It is believed that bradycardia caused by inhibitory reflex is mediated by the vagus nerve, while hypotension caused by resistance vasodilation and volume vasoconstriction is the result of inhibition of the sympathetic nerve. In addition, Fish believes that the mechanism by which HUT induces syncope is caused by activation of Bezold-Jarisch reflex.

There is no consistent standard in the methodology of the upright tilt test. There are three common methods in summary:

(1) Basic tilt test: All drugs affecting autonomic function were stopped 3 days before the test, and fasted 12 hours before the test. The child was placed supine for 5 minutes, recorded arterial blood pressure, heart rate and II lead ECG, and then stood on a sloping bed (inclination angle of 60 degrees) until a positive reaction occurred or completed for 45 minutes. During the test, blood pressure, heart rate and II lead ECG were measured once every 5 minutes from the start of the test. If the child has symptoms, he can be monitored at any time. The test was terminated immediately in the case of a positive reaction, and the child was placed in the supine position until the positive reaction disappeared and the rescue medication was prepared.

(2) Multi-stage isoproterenol tilt test: The preparation and monitoring indicators before the experiment are the same as the basic tilt test. The experiment was carried out in three stages, each stage was first placed for 5 minutes, and a drug injection (isoproterenol) was performed. After the drug was stabilized, it was tilted to 60° for 10 minutes or until a positive reaction occurred. If the previous stage is negative, the concentration of isoproterenol is sequentially increased in the order of 0.02-0.04 g/Kgmin, 0.05-0.06 g/Kgmin, and 0.07-0.10 g/Kgmin.

(3) Single-stage isoproterenol tilt test: The experimental method is the same as the multi-stage isoproterenol tilt test, but only from the third stage.

The criteria for judging the positive result of the upright tilt test are as follows:

The child has syncope or syncope during the tilting process (dizziness and often accompanied by one or more of the following symptoms: decreased vision, hearing loss, nausea, vomiting, sweating, unstable standing, etc.) accompanied by the following conditions One:

1, diastolic blood pressure;

2, sinus bradycardia (4-6 years old: heart rate sinus arrest > 3 seconds or more;

3, transient II degree or more than atrioventricular block;

4, borderline rhythm (including escape heart rate and accelerated autonomic heart rate).

Type of reaction: According to changes in blood pressure and heart rate during the test, the positive reactions were divided into the following three types:

(1) Cardiac-suppressed response, characterized by a sharp drop in heart rate, showing bradycardia and no decrease in systolic blood pressure;

(2) Angiostatin-type response, blood pressure decreased significantly, with heart rate increased;

(3) Mixed reaction, blood pressure and heart rate were significantly decreased.

The duration and tilt angle of the upright tilt test vary from one report to another. Most scholars advocate that it is more appropriate to tilt 60°-80°. Fitzpatrick et al. compared the different tilt angles, different times, and experimental choices, demonstrating that the syncope patient tilted 60° for 45 minutes, and the average time to induce a positive reaction was 24.5 minutes with a specificity of 93%. According to the research of Pediatrics of Peking University First Hospital, according to the characteristics that children are not easy to tolerate long-term examination, the design of tilting 60° for 45 minutes is selected, which is in line with pediatric characteristics and easy to promote.

Differential diagnosis

For children with repeated syncope episodes, after detailed medical history, understand the symptoms and signs at the time of onset, and then through the necessary auxiliary examinations such as electrocardiogram, EEG, biochemical examination and upright tilt test, it is not difficult to diagnose, but with Identification of the following diseases:

1. Cardiac syncope: The disease is caused by a sudden decrease in cardiac output caused by heart disease or a pause in blood flow, leading to cerebral ischemia. More common in severe aortic valve or pulmonary stenosis, atrial myxoma, acute myocardial infarction, severe arrhythmia, QT interval prolongation syndrome and other diseases. It is easy to identify by carefully asking about medical history, physical examination, and ECG changes.

2, hypoglycemia: This disease often has a history of hunger or the use of hypoglycemic drugs, mainly manifested as fatigue, sweating, hunger, and then appear syncope and unconsciousness, slow syncope, blood pressure and heart rate during the attack Change, can be unconscious, test blood sugar lower, intravenous glucose quickly relieve symptoms.

3, epilepsy: for patients with convulsive syncope episodes of vasovagal syncope should pay attention to the identification of epilepsy, by doing EEG, upright tilt test is not difficult to identify.

4, erect regulation disorder: the child manifested by the erect position of the erect position or the erect time may be slightly longer may have dizziness, vertigo, chest discomfort and other symptoms, severe cases may have nausea, vomiting, or even faint, no treatment can Get awake quickly and return to normal. It can be identified by an upright test, an upright tilt test, or the like.

5, rickets syncope: The disease has obvious mental factors before the onset, and before the crowd. When you have a seizure, you are conscious, have a breath or excessive ventilation, your limbs are struggling, your eyes are tight, and your face is flushed. The pulse and blood pressure are normal, and there are no pathological neurological signs. The episodes last for several minutes to several hours. After the attack, the mood is unstable. If there is fainting, it will be slow and will not be injured. It often has a similar history and is easy to vaginal. Sexual syncope identification.

6, in addition, the disease should be differentiated from hyperventilation syndrome.

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