![]() ![]() Most of these are related to rhythm disturbances which are secondary to inherent cardiac disease. Two-thirds of dogs and cats with syncope also have a cardiac disease. The most common causes we see in our patients are cardiogenic in nature. A sudden decrease in cardiac output (CO) or vascular resistance reduces mean arterial pressure may both result in reduction of cerebral blood flow. The vast majority of syncopal events in veterinary medicine are due to a transient reduction in brain blood flow. There are numerous diseases that can result in any one or a combination of these mechanisms. These mechanisms usually involve reduced cardiac output resulting from arrhythmias or decreased cardiac filling, obstruction of blood flow from the heart, hypoxia or hypoglycemia (with normal cerebral flow) or severe decreased vascular resistance related to neurocardiogenic reflexes. The mechanisms underlying syncope are usually rather acute in nature. Typically CSE are preceded by loss of muscle tone whereas seizure activity is usually preceded by atypical limb or facial movement or even staring spells prior to the loss of body tone. What may often confuse one who witnesses a syncopal event is that on occasion some animals may have "convulsive syncopal episodes" (CSE) that results from severe hypotension or asystole. However it is uncommon to see persistent facial fits, persistent tonic/cloned motion, defecation, postictal dementia and neurologic deficits with cardiovascular mediated syncope. This number may be due to the fact that one it is a referral database and two that often to both the trained and untrained eye it may be difficult to distinguish syncope from seizure activity.ĭuring a syncopal event, animals will usually collapse into lateral recumbency and may have concurrent stiffening of the limbs, opisthotonous, urination and vocalization. The true incidence of syncope is unknown however it has been reported to occur in a referral database in 0.15% of dogs and 0.03% of cats. The therapy of vasovagal syncope, which is based on beta-blockers, scopolamine, dysopiramide and plasma expanders, is reviewed.Syncope is the sudden temporary loss of consciousness that is associated with loss of postural tone as a result of an abrupt decrease in cerebral perfusion or decreased delivery of essential nutrients (i.e. The medical history, clinical examination, electro- and echocardiogram, chest x-ray identify two main groups of patients (with or without cardiopathy) who will follow different diagnostic protocols. In this review a diagnostic pattern for the assessment of the vasovagal syncope is suggested. Others suggest that a reduction in the sympathetic drive to the vessels, responsible for a progressive hypotension in the minutes preceding syncopal episodes, is the origin of the reduced venous return. The discussion is still open about the origin of the reduced venous return: it probably originates from a redistribution in the blood volume, due to a venous pooling in the lower limbs or from a reduced muscle tone, because many subjects with vasovagal syncope are slender and with less developed muscle apparatus. These autonomic changes are responsible for a sudden hypotension and bradycardia. The powerful contraction around an almost empty cardiac chamber induces the activation of ventricular mechanoreceptors, and through a reflex mechanism, a sudden increase in the vagal and a sudden reduction in the sympathetic drive. The nature of the vasovagal reflex is now better understood: in subjects with vasovagal syncope, during prolonged orthostasis, it was observed a fall in the venous return, inducing an increased sympathetic drive to the heart (with positive inotropic and chronotropic effect) and a lower ventricular filling. The transitory loss of consciousness during prolonged orthostasis is typically associated with sudden hypotension and bradycardia, which are commonly preceded by relative tachycardia and by premonitory symptoms such as pallor, nausea, asthenia, yawns, hyperventilation, mydriasis, humming, lasting several minutes. The vasovagal syncope can be clinically diagnosed by means of the tilt test. The nature of most syncopal episodes, previously unknown, was recently elucidated by new diagnostic techniques such as the use of the tilt test. ![]()
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