The causes of collapse can be broadly categorised into : syncope, weakness and seizures.

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1 VICAS Winter Conference 2010 Cork, Ireland Mike Martin COLLAPSE & ARRHYTMIAS Mike Martin MVB, DVC, MRCVS. Specialist in Vet Cardiology Veterinary Cardiorespiratory Centre, Thera House, Kenilworth, Warwickshire. This lectures reviews my experience in dogs that present with collapse. Movies will be shown of dogs with both syncope and seizure and the differences discussed. It can be difficult to interpret from an owners description and/or take a history to obtain a reliable description, of a collapse episode. Conseqently, differentiating between sycnope (cardiogenic faint) and true seizures (fits) is often difficult. And in some cases the dog may simple have an episode of weakness, that can mimick collapse. The causes of collapse can be broadly categorised into : syncope, weakness and seizures. Syncope Syncope (fainting) is a sudden, transient loss of consciousness that occurs when cerebral blood flow falls. The reduced blood flow results in a deprivation of energy substrates (oxygen or glucose) which impairs cerebral metabolism. These are often cardiovascular diseases. It should be noted that an acute reduction in cardiac output causes mucous membrane pallor; in contrast cyanosis is more commonly associate with respiratory disease. Causes of syncope Vasovagal syncope (aka: neurally mediated syncope, vasodepressor syncope and faint) - Transient bradycardia and/or systemic hypotension - Triggered by a surge of catecholamines, such as with excitement or sudden exercise. This appears to be a common cause of fainting in Boxers - Tussive-syncope - collapse follows a paroxysm of coughing - Micturition-syncope collapse follows straining to urinate Reduced cardiac output - Profound bradyarrhythmias, eg. sinus arrest. - Profound tachyarrhythmias, eg. ventricular tachycardia - acute forward failure on exertion - Inadequate cardiac output (forward failure) on exertion: dilated cardiomyopathy, hypertrophic obstructive cardiomyopathy, pericardial effusion, aortic stenosis, pulmonic stenosis Hypoxia

2 - Hypoxia can occur with hypoventilation (upper airway obstruction), diffusion abnormalities and ventilation/perfusion mismatch as occurs with severe lung parenchymal disease or cor pulmonale. - Cyanosis is often found with severe airway obstructive disorders such as laryngeal paralysis, tracheal collapse and brachycephalic upper airway syndrome. - While right to left cardiac shunts are rare, they tend to produce cyanosis with polycythaemia. - Anaemia or acute haemorrhage may lead to collapse, often easily recognised but in some case an abdominal bleed can be quite subtle such as haemorrhage due to a splenic haemangiosarcoma. Hypoglycaemia - Insulinoma - Insulin overdose in a diabetic animal. - Working dog hypoglycaemia - Other causes are much less common and include liver disease and sepsis Pre-syncope Transient partial reduction in blood flow to the brain, then an absolute syncopal episode may not occur, but an episode of weakness or ataxia may be the presentation. For example: - Rapid supraventricular tachycardia (SVT) - Dilated cardiomyopathy - Pericardial effusion Weakness Weakness is defined as a loss of muscular strength resulting in an animal becoming completely or partially recumbent, or ataxic. Generalised muscle weakness is referred to as asthenia. Weakness can be continuous or episodic. Many conditions produce a continuing weakness due to advanced disease and the diagnosis is often more apparent (eg. kidney or liver disease, haemorrhage). Heart failure also produces weakness (forward failure). On exertion or exercise the animal becomes weak and may become recumbent (appear to collapse). Causes of weakness Many neurological or neuromuscular diseases can result in weakness - Disorders of neuromuscular transmission Myasthenia gravis - Myopathies Polymyopathy or polymyositis Labrador and golden retriever myopathy Hypokalaemic polymyopathy in cats. - Exercise induced collapse (EIC) - Peripheral neuropathies Non-cardiorespiratory medical conditions 2

3 A variety of medical conditions (eg. endocrinopathies and metabolic diseases) can result in weakness and occasionally collapse, and include: - Hyperkalaemia often results in bradyarrhythmias Addison's disease diabetic ketoacidosis acute/oliguric renal failure obstructive urinary disorders) - Hypocalcaemia - Hypothyroidism may lead to bradyarrhythmias - Hyperadrenocorticism - Phaeochromocytoma - Hyperthermia ( heat stroke ) - Polycythaemia - Severe acid base imbalance Seizures Seizure (epilepsy, fit, convulsion) refers to an involuntary, paroxysmal and uncontrolled muscular activity due to a disturbance in the brain s activity. Seizures can be divided into generalised tonic-clonic (grand mal) or partial seizures (petit mal). The latter can present as a transient loss of consciousness. The classical grand mal seizure is relatively easy to recognise - tonic/clonic contractions, defaecation, a pre-ictal phase and post-ictal dementia or abnormal behaviour are often noted with generalised seizures. - Central CNS disorders hepatic encephalopathy narcolepsy or cataplexy Scottie cramp episodic falling over in Cavalier King Charles Spaniels Partial seizures are relatively rare, but can mimic syncope. Recommended Reading Notes on Cardiorespiratory Diseases of the Dog and Cat, 2 nd edition. Martin & Corcoran (2006) Blackwell Science. ISBN Small Animal ECGs: An Introductory Guide, 2 nd edition. Mike Martin (2007), Blackwell. ISBN

4 Syncope Triggers Excitement: greeting O, start of exercise, rising from rest, no trigger At start Preceded by ataxia or sudden thump to floor Initial phase of collapse Flaccid: sleep-like, dead-like During collapse Unresponsive, eyes can be open (gazing), urination If conscious: struggles to stand (mimic seizure) Mucosal pallor Brief in duration Prolonged Opisthotonus develops Recovery Return on consciousness, looks around, wobbles to feet, stands with ataxia, but for a short duration Often 100% recovery, but may go to bed or continue to play 4

5 Seizure Triggers Often spontaneous, rest, relaxed, sleep, familiar environment At start Prodromal phase, awareness something is about to happen During collapse Unresponsive, eyes can be open (gazing), urination Tonic clonic limb movement Salivation Head not back in opithotonus Often in excess of a minutes, ie. not brief Recovery Prolonged period of being out of sorts, disorientated 5