Syncope in Cavalier King Charles Spaniels
Cavalier King Charles spaniels with mitral valve murmurs from Grade 3 through Grade 6 and enlarged atrial chambers may lose consciousness or display episodic weakness, especially of the hindquarters, ataxia (an inability to coordinate muscular movements), or collapse. This disorder, when loss of consciousness occurs, is called syncope; absent the loss of consciousness, it is called presyncope.
Technically, syncope is the temporary loss of consciousness, or fainting, due to a sudden decline in blood flow to the brain. It is not unique to dogs with heart disorders and generally may be referred to as canine syncope syndrome.
In cavaliers, syncope and presyncope are associated with Mitral Valve Disease because in mid- to late stages of MVD, when the affected dog experiences excessive excitement, stress, or sudden shock, the heart and blood vessels are prompted to constrict, with the heart rate increasing suddenly, depleting the blood volume from the left ventricle and in the blood vessels to the brain. Syncope associated with the heart's reaction to MVD is called vasodepressor syncope.
Common factors which may precipitate vasodepressor syncope in cavaliers with mid- to late stage MVD are excessive exercise, running, stress, coughing, barking, urination, defecation, or pain. Even grooming or bathing, if stressful to the dog, could prompt syncope. Treatment for syncope involves treating the underlying disorder, which in the case of cavaliers suffering from MVD would be treatment of that disease, including adjustment of the medication. Also, cavaliers in the advanced stages of MVD should avoid stress, excitement, and coughing, and excessive exercise.
►January 2014: Holter monitoring shows MVD dogs with syncope had less sinus arrhythmia, and decreased overall heart rate variability. In an international study published in January 2014, of 43 dogs with advanced MVD, which included 21 dogs (6 cavaliers) with syncope and 22 dogs (10 CKCSs) without syncope, cardiologists found that:
"Compared with dogs without a history of syncope, dogs with advanced MMVD and a history of syncope did not have a higher occurrence of arrhythmias, but had less sinus arrhythmia, and had changes in HRV variables representing decreased overall HRV, decreased parasympathetic, and increased sympathetic modulation of heart rate."
Clinical usefulness of cardiac event recording in dogs and cats examined because of syncope, episodic collapse, or intermittent weakness: 60 cases (1997-1999). Bright JM, Cali JV. J Am Vet Med Assoc 2000; 216:1110-1114.
Chronic valvular heart disease in dogs. Rush J.E.. In: Proceedings of the 26th Annual Waltham Diets; OSU Symposium for the Treatment of Small Animal Cardiology, pp. 1-7, 2002.
Mitral valve prolapse in Cavalier King Charles Spaniel: A review and case study. Hyun C. J. Vet. Sci. 2005 Mar;6(1):67-73.
Differential diagnosis of collapse in the dog 3. Cardiovascular and miscellaneous causes. Wray,J, In Practice, 31 Mar 2005;27(3): 128-135(8).
Recurrent syncope: only the heart was considered. Peter Stiefelhagen. MMW Fortschr Med. 2006 Sep 28;148 (39):21.
Syncope in Small Breed Dogs. Marc S. Kraus, Anna R.M. Gelzer. Clinicians Brief. Aug 2009.
A retrospective study of 153 cases of undiagnosed collapse, syncope or exercise intolerance: the outcomes. L. Barnett, M. W. S. Martin, J. Todd, S. Smith, and M. Cobb. J.Sm.Anim.Prac. (Jan 2011) 52(1):26–31. Quote: "Objectives: To retrospectively assess the long-term outcome for dogs that were presented with collapse, syncope or exercise intolerance for which an underlying cause is not identified. ... Results: One hundred and fifty-three cases were successfully followed up. Clinical signs had resolved in 64 cases (42%), 35 dogs (23%) were continuing to exhibit clinical signs, although 22 of these had improved without medical intervention. In 17 cases (11%), a diagnosis had subsequently been made or treatment was being administered and 37 dogs (24%) had died. Of the deaths, 18 (12%) were considered to be related to the original presentation. The overall prevalence of death and deterioration related to the problems investigated was 16·2% of cases. Death in boxers was significantly more common than in other breeds (36%). ... Age at death ranged from 8 months in a cavalier King Charles spaniel to 17 years 3 months in a border collie. ... A total of 21 of the 37 dogs which had died (56·8%) were over the age of 10 at death. Of the 16 dogs that died before 10 years of age, ... two were cavalier King Charles spaniels ... . Clinical Significance: Death and deterioration are uncommon outcomes for dogs other than boxers presenting with collapse, syncope and exercise intolerance for which a definitive diagnosis cannot be made."
Holter Monitoring of Small Breed Dogs with Advanced Myxomatous Mitral Valve Disease with and without a History of Syncope. C.E. Rasmussen, T. Falk, A. Domanjko Petrič, M. Schaldemose, N.E. Zois, S.G. Moesgaard, B. Åblad, H.Y. Nilsen, I. Ljungvall, K. Höglund, J. Häggström, H.D. Pedersen, J.M. Bland and L.H. Olsen. J.Vet.Int.Med. Jan. 2014. Quote: "Background: Syncope is a transient loss of consciousness occasionally occurring in dogs with advanced myxomatous mitral valve disease (MMVD). Objective: (1) To study ECG changes during syncopal episodes in dogs with advanced MMVD and (2) to compare the occurrence of arrhythmias and changes in heart rate variability (HRV) between dogs with advanced MMVD with and without a history of syncope. Animals: Forty-three privately owned dogs (<15 kg) with advanced MMVD: 21 with [including 6 cavalier King Charles spaniels] and 22 without a history of syncope [including 10 CKCSs]. Methods: Prospective study with dogs recruited for an evaluation including history, physical examination, echocardiography, and arrhythmia and HRV analysis performed on 24-hour Holter recordings. Results: A syncopal episode was observed during Holter monitoring in 4 dogs: 3 dogs had sinus rhythm and 1 dog had sinus arrest followed by escape rhythm. An arrhythmia variable representing sinus arrhythmia was significantly lower in dogs with a history of syncope than in those without (P = .008). Eight of 26 HRV variables were significantly different between dogs with and without a history of syncope. Conclusions and Clinical Importance: Compared with dogs without a history of syncope, dogs with advanced MMVD and a history of syncope did not have a higher occurrence of arrhythmias, but had less sinus arrhythmia, and had changes in HRV variables representing decreased overall HRV, decreased parasympathetic, and increased sympathetic modulation of heart rate."