Episode from the podcastVETgirl Veterinary Continuing Education Podcasts

Holter monitoring in dogs with mitral valve disease | VETgirl Veterinary CE Podcasts

Released Monday, 17th August 2015
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In this VETgirl podcast, we review the clinical utility of Holter monitoring in dogs with advanced myxomatous mitral valve disease with or without a history of syncope. Syncope - or fainting - is characterized by a transient loss of consciousness and is generally considered of cardiac or non-cardiac etiology (e.g., neurologic, pulmonary, etc.). Syncopal episodes typically have short duration, rapid recovery, and lack of aura or post-ictal phase. Causes for syncope secondary to cardiac causes is believed to be due to reduced blood flow/nutrient delivery to the brain and can occur for a variety of reasons in patients with cardiac disease. Arrhythmias (either bradyarrhythias or tachyarrhythmias) represent one category of etiologies of cardiac syncope. Determining the exact etiology of syncope via Holter monitoring can be challenging due to the sporadic nature of syncope as a clinical sign and the relatively short duration (24 hours) of most Holter monitor recordings. In other words, it's often hard to catch, even with a Holter! Syncope is associated with increased mortality in dogs with mitral valve disease (MVD). Heart rate variability (HRV) is a complex parameter with many variables that quantifies beat-to-beat rhythmic variability over time. This rhythmic variability is dictated by the two branches of the autonomic nervous system (parasympathetic and sympathetic). Heart rate variability is decreased in dogs with congestive heart failure secondary to MVD, and is associated with an increased risk of death in experimental canine myocardial infarction and various forms of human cardiac disease. So, Rasmussen et al wanted to evaluate the presence of arrhythmic activity and heart rate variability in dogs with stable congestive heart failure secondary to advanced MVD. In this prospective study, they evaluated 42 dogs: 20 with syncope and 22 without syncope. Dogs had the following assessed in this study: history, physical examination, echocardiography, and 24-hour Holter recording (to evaluate for the presence of arrhythmia and heart rate variability analysis). So what'd they find? Overall, there was no significant difference in incidence or severity of pulmonary arterial hypertension between groups. In this study, only 4 dogs experienced a syncopal event during the Holter recording period; of these dogs, one experienced an arrhythmic event at the time of syncope, while the other 3 dogs had normal sinus rhythm at time of syncopal event. Between the two groups (e.g., syncopal vs. non-syncopal), there was no significant difference in arrhythmic activity, and overall, evaluation of heart rate variability (HRV) indicated a statistically lower HRV and incidence of sinus arrhythmia overall in dogs with syncope. So it turns out that dogs with advanced MVD and a history of syncope had reduced heart rate variability overall compared with dogs without syncope and that there was no difference in actual arrhythmic activity. Findings suggest that dogs with syncope and advanced MVD have reduced parasympathetic (and increased sympathetic) influence on cardiac rhythm and may be less likely to have arrhythmic etiologies for their syncope. The complex parameter of HRV in this study is used to evaluate a relatively simple concept: the relative influence of parasympathetic and sympathetic influence on cardiac rate and rhythm. The study results suggest that dogs with syncope and advanced MVD have reduced parasympathetic influence than their counterparts without syncope. We know that parasympathetic influence decreases with severity of cardiac disease (thus the reason an active CHF patient generally does not have a sinus arrhythmia on presentation - and are often tachycardiac) so the results of this study may simply reflect that dogs with syncope have more advanced disease. It could also suggest that the reduced parasympathetic activity plays a causal role in the syncope, but this is speculation only. The lack of significant difference in arrhythmic acti

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