Syncope is a syndrome of decreased blood supply to the whole cerebral hemisphere and brainstem, resulting in episodic transient loss of consciousness with loss of postural tone, which can be caused by vasovagal reflexes, upright hypotension, decreased cardiac output causing whole brain hypoperfusion, or by selective brainstem hypoperfusion due to vertebrobasilar artery ischemia.
Clinically, they can be divided into three categories according to the etiology and pathogenesis.
1, reflex syncope: due to blood pressure regulation, heart rate reflex arc dysfunction and autonomic insufficiency resulting in a sudden drop in blood pressure and a sudden decrease in cardiac output. These include vasovagal syncope (simple syncope), upright hypotensive syncope, idiopathic hypotensive syncope, carotid sinus syncope, urinary syncope, swallowing syncope, cough syncope, and glossopharyngeal neuralgia syncope.
(1) Vasovagal syncope (simple syncope): It can be seen in all ages, mostly in young and frail women, and the attacks often have obvious triggers (such as pain, emotional stress, fear, minor bleeding, various punctures and minor surgeries, etc.), and are more likely to occur in hot and muggy weather, dirty air, fatigue, fasting, insomnia and pregnancy. The syncope is preceded by dizziness, vertigo, nausea, epigastric discomfort, pallor, limb tenderness, fidgeting and anxiety, and lasts for several minutes followed by a sudden loss of consciousness, often accompanied by a drop in blood pressure and a weak pulse, which can wake up spontaneously after a few seconds or minutes, without sequelae. The mechanism of occurrence is due to various stimuli through the vagal reflex, causing transient vascular bed dilation, reduced return blood volume, reduced cardiac transfusion bleeding, and decreased blood pressure resulting in insufficient cerebral blood supply.
(2) Upright hypotension (postural hypotension): manifests as syncope when there is an abrupt change in position, mainly when standing up suddenly from a lying or squatting position. It can be seen in.
① certain people who stand in a fixed position for a long time and those who are bedridden for a long time.
②Taking certain drugs, such as chlorpromazine, guanethidine, nitrites, or post-sympathectomy patients.
③ Certain systemic diseases, such as spinal cavernous disease, polyneuritis, cerebral atherosclerosis, recovery from acute infectious diseases, chronic malnutrition, etc. The mechanism of occurrence may be due to factors such as low venous tone in the lower extremities, blood accumulation in the lower extremities (postural), dilated peripheral vascular stasis (taking nitrite drugs), or impaired reflex regulation of blood circulation, resulting in decreased return blood volume, decreased cardiac output, and decreased blood pressure leading to insufficient cerebral blood supply.
(3) Carotid sinus syndrome: Due to lesions near the carotid sinus, such as local arteriosclerosis, arteritis, lymphadenitis or lymph node enlargement around the carotid sinus, tumor and scar compression or stimulation of the carotid sinus, resulting in vagal nerve excitation, heart rate slowdown, reduced cardiac output, and blood pressure drop, resulting in insufficient cerebral blood supply. It may manifest as episodic syncope or with convulsions. The common triggers are hand pressure on the carotid sinus, sudden head turn, and tight collar.
(4) Urinary syncope: Mostly seen in young men, it occurs during or at the end of urination, lasts about l-2 min, and awakens on its own without sequelae. The mechanism may be comprehensive, including autonomic instability, sudden change of position (getting up at night), breath-holding action during urination or reduction of cardiac output by vagal reflex, blood pressure drop, and cerebral ischemia.
(5) Cough syncope: seen in people with chronic lung disease and occurs after a violent cough. The mechanism may be due to increased intrathoracic pressure during severe coughing, obstruction of venous blood return, decreased cardiac output, decreased blood pressure, and cerebral ischemia, or a rapid increase in cerebrospinal fluid pressure during severe coughing, resulting in a shocking effect on the brain.
2, cardiogenic syncope: occurs rapidly, without any premonition, unrelated to upright position, motion-induced syncope suggests cardiac causes, but also various heart diseases are unique features.
(1) Cardiac arrhythmias
① Slow arrhythmias: bradycardia and arrest, sick sinus syndrome, heart block, etc.
(2) Rapid arrhythmias: paroxysmal supraventricular tachycardia, ventricular tachycardia, etc.
(3) Long QT syndrome
(2) Instrumental heart disease
① Acute cardiac output obstruction Left ventricular outflow tract obstruction: aortic stenosis, left atrial mucus aneurysm, valve thrombosis, etc Right ventricular outflow tract obstruction: pulmonary stenosis, primary pulmonary hypertension, pulmonary embolism, etc
② Cardiomyopathy and congenital heart disease: acute myocardial infarction, Fallot’s tetralogy, etc. 3, cerebral syncope As a result of circulatory disorders in the blood vessels of the brain or blood vessels supplying blood to the brain, resulting in momentary widespread cerebral insufficiency of blood supply.
For example, cerebral arteriosclerosis causes narrowing of the lumen, hypertension causes cerebral artery spasm, migraine and basilar artery diastolic disorder in cervical spondylosis, and various causes of cerebral artery microembolism, arteritis and other lesions can cause syncope. Among them, transient ischemic attack can manifest as a variety of neurological dysfunction symptoms. The manifestations are diversified due to different damaged blood vessels, such as hemiparesis, limb numbness, speech impairment, etc.
3. Other syncope: such as crying syncope (emotional response), hyperventilation syndrome, hypoglycemic syncope and severe anemic syncope.
The presence of head-heavy prodromal symptoms before loss of consciousness suggests syncope caused by cerebral underperfusion, usually due to vasovagal emission, upright hypotension or cardiac insufficiency. Episodic loss of consciousness in the recumbent position can exclude vasovagal reflexes and upright hypotension, etc., and may be due to cardiac insufficiency or seizures. Exercise-induced syncope is suggestive of cardiac origin.