Jordi López-Alvarez, from Davies Veterinary Specialists, works through the causes of the transient loss of consciousness.
This article © Jordi Lopez-Alvarez
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Paroxysmal dyskinesias are episodic movement disorders in which abnormal movements are present only during attacks. Some breeds appear over-represented. Although increasingly being recognized, these are often poorly characterized in veteinary literature and are commonly mistaken for an epileptic seizure or even pre-syncopal episodes.
Patent ductus arteriosus is one of the most common congenital cardiac abnormalities in the dog. A small proportion of these congenital abnormalities are associated with pulmonary hypertension and reversal of the direction of blood from the pulmonic to the systemic circulation (right-to-left shunting PDA). This causes cyanosis, secondary polycythaemia, exercise intolerance, intermittent hindlimb weakness, syncope and even hyperviscosity and seizures.
Aortic thromboembolism is a relatively common complication of feline hypertrophic cardiomyopathy. In dogs, it is much less common and generally no underlying cardiac condition is found in these cases. There may be a breed predisposition for the Cavalier King Charles Spaniel and an association with Cushing's syndrome and hypercoagulable status has been suspected. The embolism of the iliac bifurcation can be subtle, causing mild, uni- or bilateral weakness, or severe, causing complete bilateral paralysis of the hindlimbs; this may be reversible if enough collateral circulation resumes the oxygen provision to the legs or may remain irreversible in a number of cases.
The Boxer is particularly prone to present with collapsing episodes. As part of the work-up investigations, Holter monitor during normal daily activities of the dog (including exercising) as well as recording a video of events to better illustrate these episodes. Vasovagal syncope, subaortic stenosis causing reduced cardiac output and ventricular tachycardia secondary to arrhythmogenic right ventricular cardiomyopathy are the most common causes of syncope in this breed.
