Synkopen - eine systematische Übersicht zur Klassifikation, Pathogenese, Diagnostik und Therapie

Zusammenfassung

Als Synkope wird die vorübergehende Unterbrechung der Hirndurchblutung mit konsekutivem Verlust des Bewusstseins, des Haltetonus, aber auch spontaner Erholung bezeichnet. Etwa ein Drittel der Bevölkerung erleidet einmal im Leben eine Synkope. Vor dem Bewusstseinsverlust treten Prodromi auf, wie Schwächegefühl, Kopfschmerzen, Sehstörungen, Schwitzen, Übelkeit; anschließend bestehen Müdigkeit, Kopfschmerzen, gelegentlich Übelkeit oder Unruhe. Pathogenetisch lassen sich kardiovaskuläre, nicht kardiovaskuläre und ungeklärte Ursachen unterscheiden. Unter kardiogenen Ursachen sind strukturelle Herzerkrankungen, koronare Herzkrankheit und Rhythmusstörungen zu nennen. Nicht-kardiovaskuläre Synkopen sind neurologisch, metabolisch, psychiatrisch-psychogen oder psychosomatisch bedingt.

Zu den häufigsten Ursachen von Synkopen zählt die orthostatische Hypotonie. Ihre Ursachen sind vielfältig und umfassen neurologische und internistische Erkrankungen. Nach plötzlichem Aufstehen kommt es zu obigen Prodromi und dann zum Bewusstseinsverlust, der Blutdruck fällt deutlich ab, meist steigt die Herzfrequenz nicht an. Die autonome Testung zeigt oft eine Einschränkung der autonomen kardiovaskulären Modulation.

Bei vielen Patienten mit scheinbar „ungeklärter Synkope” liegen neural-vermittelte Synkopen (neurally mediated syncope) oder neurokardiogene bzw. vasovagale Synkopen vor. Meist ist die Herz-Kreislaufregulation unter orthostatischer Belastung über längere Zeit zunächst stabil. Erst nach längerer orthostatischer Belastung fallen Blutdruck und Herzfrequenz plötzlich ab. Oft findet sich unmittelbar vor der Synkope eine autonome Überaktivität. Neurokardiogene Synkopen treten unter emotional belastenden und schmerzhaften Situationen auf oder - als sogenannte „Situations- oder Reflex-Synkopen” - nach langem Stehen, während Miktion, Defäkation, Husten und Niesen oder im Zusammenhang mit einer Trigeminus- oder Glossopharyngeus-Neuralgie. Die Entstehungsmechanismen der neurokardiogenen Synkopen sind zum Teil noch ungeklärt.

Diagnostisch ist eine Kipptischuntersuchung mit 60 °-Neigung des Patienten hilfreich. Die Sensitivität dieser Untersuchung kann durch die gleichzeitige Gabe einer Synkopen-provozierenden Medikation oder durch zusätzliche orthostatische Belastung mittels Unterdrucksaugung im Bereich der unteren Körperhälfte erhöht werden.

In der Behandlung von Synkopen sind zuerst nicht-pharmakologische Maßnahmen angezeigt. Bei orthostatischen Regulationsstörungen sind plötzliches Aufstehen sowie Situationen, die zur Vasodilatation der Hautgefäße führen, z. B. hohe Umgebungstemperaturen, zu vermeiden. Kochsalzreiche Diät und Flüssigkeitszufuhr sowie leichte körperliche Übungen oder sogenannte „counter-maneuvers” sind oft hilfreich. Medikamentös werden z. B. Mineralokortikoide, vasokonstriktorische, α₁-Adrenozeptor simulierende Substanzen (Ephedrin oder Midodrin), Adenosin-blockierende Medikamente wie Theophyllin, aber auch β₂-Blocker sowie anticholinerge Substanzen wie Scopolamin oder Disopyramid, zentral wirksame, selektive Serotonin-Wiederaufnahmehemmer (z. B. Fluoxetin oder Sertralin), der α₂-Agonist Clonidin, aber auch Stimulanzien wie Methylphenidat empfohlen. Herzschrittmacher scheinen eher zu ungezielt und zu häufig empfohlen zu werden.

Das intravaskuläre Volumen kann auch durch vasopressorische Substanzen, z. B. das antidiuretisch wirksame Vasopressin-Analogon Desmopressin erhöht werden. Erythropoetin soll positive Wirkung auf Hämatokrit, Blutdruck und zerebrale Oxygenierung entfalten. Zur Behandlung der postprandialen Hypotonie werden u. a. das Somatostatin-Analogon Octreotid, Prostaglandin-Synthesehemmer, z. B. Indomethacin oder Ibuprofen, Metoclopramid sowie Kaffee-Konsum empfohlen.

Abstract

Syncope is defined as a temporary interruption of cerebral perfusion with a sudden and transient loss of consciousness and spontaneous recovery. Approximately one third of the population experiences syncope at least once during a lifetime.

Presyncopal signs and symptoms, including weakness, headache, blurred vision, diaphoresis, nausea, and vomiting are sometimes present for seconds or minutes prior to loss of consciousness. After syncope, the patients may present with persisting drowsiness, headache, dizziness, nausea, but not usually confusion.

Causes of syncope have been categorized as cardiovascular, non-cardiovascular, and unexplained. Cardiovascular causes can be subdivided into structural heart disease, coronary heart disease, and arrhythmia. Non-cardiovascular causes include neurological, metabolic, psychiatric and other disorders.

Orthostatic hypotension - one of the most frequent causes of syncope - has manifold etiologies comprising various neurological and internal diseases. Orthostatic hypotension usually can be attributed to an impairment of peripheral vasoconstriction or to a reduction of the intravascular volume. Signs and symptoms, including the above prodromi are often present just after rising from a supine or sitting position. Frequently, blood pressure decreases significantly without an increase in heart rate. Autonomic cardiovascular modulation is often reduced.

Many of the patients with “unexplained” syncope experience neurally mediated (i. e. neurocardiogenic or vasovagal) syncope. In these patients, cardiovascular control may be stable for an extended period of time during orthostatic stress, then there is a sudden decrease in blood pressure and heart rate. Neurocardiogenic or neurally mediated syncope can be associated with painful or emotionally stressful situations such as anxiety or fear, with prolonged standing or specific trigger situations such as micturition, defecation, coughing or sneezing, visceral or carotid sinus stimulation, or with trigeminal or glossopharyngeal neuralgia. So far, the mechanisms of neurocardiogenic syncope are not completely understood.

The passive 60 ° to 70 ° head-up tilt test is useful for the diagnosis of orthostatic and neurally mediated syncope. The sensitivity of the test can be improved by additional pharmacological provocation, e. g. by isoproterenol, or by increased orthostatic stress using lower body negative pressure stimulation.

For the treatment of syncope one should first consider non-pharmacological options. Patients with orthostatic hypotension should avoid rapid changes of the body position from supine to standing, as well as high room temperature or other situations inducing peripheral vasodilatation. An increased intake of sodium and fluids, mild physical exercise or so-called postural counter-maneuvers can improve orthostatic tolerance.

Among the drugs recommended for pharmacologic treatment are mineralocorticoids (e. g. fludrocortisone), vasoconstrictor agents (e. g. ephedrine, midodrine), adenosine receptor blockers (theophylline) and β₂-blockers (propanolol), anticholinergic agents, e. g. scopolamine or disopyramide, and negative cardiac inotropes, e. g. β₁-adrenergic blockers or disopyramide. Serotonin reuptake inhibitors (e. g. fluoxetine, sertraline), α₂-adrenergic agonists (clonidine), central nervous system stimulants such as methylphenidate or phentermine are thought to be beneficial in specific cases. Cardiac pacemakers often seem to be recommended without adequate indication.

The antidiuretic, V2-receptor specific, vasopressin analogue desmopressin increases the intravascular volume. Erythropoietin improves anemia and red blood cell decrease and augments blood pressure and cerebral oxygenation. In postprandial hypotension, octreotide, a somatostatin analogue, prostaglandin inhibitors such as indomethacin or ibuprofen, as well as metoclopramide or two cups of coffee per day might be beneficial.

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