![]() ![]() ![]() Nine of the 9 SSS dogs were treated with medical therapy as a bridge until PAP was necessary (which averaged 11 months until PAP was performed). Two dogs were euthanized due to progressive syncope. Approximately half of these SSS dogs (n=21/46) were treated lifelong with medical therapy only of these, 10 had adequate control of their syncope until the time of their death. These medications were prescribed in 49 dogs (the majority having SSS, n=46) with the goal of decreasing the frequency of syncope (SSS) or increasing the baseline heart rate (SND). Medical treatment in these dogs included the use of oral positive chronotropes such as theophylline (which was used most commonly in 41/49 dogs), propantheline, hyoscyamine, and/or terbutaline. Also, 43% of dogs (40/93) had concurrent disease of a type that could contribute to elevated autonomic (vagal) tone, including general categories of respiratory, ocular, endocrine (e.g., hypothyroidism), neurologic, gastrointestinal, or neoplastic disease (e.g., adrenal mass). In this study, the majority of dogs (85%) had some degree of structural heart disease on echocardiography, but virtually all were mitral valve endocardiosis with simply varying degree of left atrial enlargement (defined as mild, moderate, or severe). The dogs with SSS were more likely to have no response to atropine as compared to SND dogs. 22% (13/59) of dogs had no response to atropine. 26/59 (44%) of the dogs had an adequate response (defined as a heart rate > 150 bpm), while 20/59 (34%) of dogs had a partial response (defined as a HR 25% improvement from baseline). Atropine response testing (when you administer 0.04 mg/kg atropine SQ) was performed in 63% (n=59) of the total dogs (of which 40 had SSS and 19 dogs had SND). 21% (n=20) of the dogs had bradycardia-tachycardia syndrome. 74/93 of these dogs had sinus arrest (which is defined as a pause longer than 2 x R-R interval) on ECG. In this study, there was no statistically significant differences in ECG or Holter monitor findings between these two groups of dogs. 34% (n=32) of the dogs were asymptomatic, and therefore classified as SND. 66% of the dogs had clinical signs of their bradyarrythmia and were therefore considered to have SSS the most common clinical signs was syncope in 95% of these dogs (58/61). Certain breeds were overrepresented, including Miniature Schnauzers, West Highland White Terriers, and Cocker Spaniels. Females were overrepresented, with 63% (n=59) being female and 37% (n=34) being male. ![]() The average age at the time of diagnosis was 11 years, with no difference between the SSS and SND group. So, what’d they find? In this retrospective study, they included a total of 93 dogs defined with SSS or SND. Surprisingly, no large-scale studies with this specific aim had been previously reported in the veterinary literature. The goal of this study was to evaluate SSS patients from the time of presentation or diagnosis through treatment (including modality), effectiveness of treatment, and overall outcome. So Ward et al out of the North Carolina State University Veterinary Hospital wanted to evaluate SSS in dogs in a paper called Outcome and survival in canine sick sinus syndrome and sinus node dysfunction: 93 cases (2002-2014), which was published in the Journal of Veterinary Cardiology in 2016. In reality, SND and SSS likely represent a continuum of conduction systemic disease. ![]() Some feel that ECG findings described above in patients with no clinical signs should be termed sinus node dysfunction (SND) as opposed to SSS, while others contend that SSS classification should also not include patients who show a response to anticholinergic administration – drugs like atropine (indicating autonomic (vagal) dysfunction). Typical ECG findings of SSS include inappropriate sinus arrhythmia (e.g., during exertion, stress, etc., when tachycardia would be expected), sinus bradycardia, sinus arrest, and in some cases supraventricular tachycardia (SVT) as part of a bradycardia-tachycardia syndrome. Definitive diagnosis of SSS technically requires electrophysiologic studies, but in most cases the practical/clinical diagnosis of SSS in dogs is made based on identification of sinoatrial dysfunction on an ECG in conjunction with clinical signs (e.g., syncope, weakness, etc). SSS is the second most common reason for permanent artificial pacemaker implantation (PAP) intervention in dogs. In this VETgirl online veterinary CE podcast, we review the outcome and survival in dogs with sick sinus syndrome, a life-threatening bradyarrhythmia.įirst, let’s review sick sinus syndrome (SSS). ![]()
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