Veterinary Medicine - January 2008 - (Page 31)

Holter recording may be a useful diagnostic test in patients with syncope and episodic weakness when the cause of syncope is not readily apparent on a static ECG.3,11 Neurally mediated bradycardia. Neurally mediated bradycardia and syncope are common in elderly smallbreed dogs.19 Situational syncopes result from vagal triggers caused by coughing, gagging, retching, vomiting, urinating, or defecating.19 Neurocardiogenic syncope is an adrenergic-triggered, vagal-re ex bradycardic syndrome associated with excitement or exertion in elderly smallbreed dogs with advanced mitral valve disease, severe left heart enlargement, and high preload.19 Other than the bradycardia during the syncopal episodes, the heart rates and rhythms of dogs with neurally mediated bradycardia are usually normal.19 Holter recording documents the heart rhythm, as would event recording during syncope. Neurally mediated bradycardia is also a cause of syncope in some largebreed dogs, notably boxers and golden retrievers.20 Some normal dogs experiencing severe ght, fright, or ight stimuli demonstrate an adrenergic-triggered, vagal-re ex bradycardia.20 When cardiomyopathy is absent, these dogs have normal echocardiogram results and no or few VPCs.20 Cardiomyopathic boxers also experience an excitementexertion-startle-triggered neurocardiogenic bradycardia but also have ventricular tachyarrhythmias of variable severity, with or without echocardiographic abnormalities.20 Cardiomyopathic Doberman pinschers can faint because of transient neurocardiogenic bradycardia in response to exertion-excitement or just because of a sudden change from less activity to more activity.11 In Doberman pinschers, neurocardiogenic bradycardia along with syncope is a marker of cardiomyopathy.11 Holter recording helps differentiate neurocardiogenic bradycardia from ventricular tachycardia when no or few VPCs occur in a dog with recent syncope.20 Bradycardia due to sick sinus syndrome. Not all bradyarrhythmias are neurally mediated. Sick sinus syndrome is usually associated with American cocker spaniels, miniature schnauzers, and West Highland white terriers. When the bradycardia of this syndrome causes syncope, it is usually apparent on a static ECG. Advanced atrioventricular (AV) conduction blocks are usually due to degeneration of conduction pathways. AV conduction blocks severe enough to cause syncope are usually evident on a static ECG. Ventricular arrhythmia due to myocardial disease. Patients with myocardial disease (most notably Doberman pinschers and boxers) may present with syncope secondary to ventricular tachycardia. When experiencing syncope, boxers may or may not have evidence of dilated cardiomyopathy (DCM), whereas Doberman pinschers almost always have in dogs with advanced heart disease. In these patients, atrial brillation is evident on a static ECG. The assumption is that poor cardiac function, loss of atrial contraction, and the rapid, irregular rhythm that result from this arrhythmia produce a marked decrease in cardiac output, resulting in syncope. However, in dogs with cardiomyopathy and atrial brillation, syncope may also result from paroxysmal ventricular tachycardia. Holter recording can be a useful tool in diagnosing syncope in which the cause is not readily apparent and is the result of atrial brillation or ventricular tachycardia.3,11-16 Screening Doberman pinschers and boxers for cardiomyopathy Cardiomyopathy is common in Doberman pinschers and boxers.7-9,12,16 Owners and breeders of Doberman pinschers and boxers have become aware of the high In Doberman pinschers, neurocardiogenic bradycardia along with syncope is a marker of cardiomyopathy. obvious DCM. In patients with syncope secondary to ventricular tachycardia, if a static ECG fails to document couplets, triplets, or ventricular tachycardia, Holter recording is indicated. Holter monitoring is especially indicated in boxers, who may have syncope secondary to neurocardiogenic bradycardia or ventricular tachycardia. Atrial ﬁbrillation due to advanced heart disease. Ventricular tachycardia is not the only tachyarrhythmia that can be associated with syncope and episodic weakness. These signs can also occur after the onset of atrial brillation incidence of cardiomyopathy in these breeds and are increasingly seeking diagnostic screening from veterinarians. The earliest marker for cardiomyopathy in these breeds is VPCs.8,9,15,16 Holter recording is a proven diagnostic procedure for detecting occult (presymptomatic) ventricular arrhythmias in Doberman pinschers and boxers.8,9,12,13 Cardiomyopathy is likely if more than 50 to 100 VPCs occur in 24 hours and if any complexity of arrhythmia, such as couplets, triplets, or ventricular tachycardia, is present, unless another cause can be discovered. We recommend all apparently healthy adult Doberman VETERINARY MEDICINE January 2008 31

Table of Contents Feed for the Digital Edition of Veterinary Medicine - January 2008

Veterinary Medicine - January 2008 Contents Digital Extra Letters Toxicology Brief Idea Exchange A Challenging Case: Phimosis in a Young Adult Dog The Indications and Technique for Continuous Ambulatory Electrocardiographic Recording in Dogs A Review of Selected Systemic Antifungal Drugs for Use in Dogs and Cats CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - January 2008

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