Identification of 2 loci associated with development of myxomatous mitral valve disease in Cavalier King Charles Spaniels.

Myxomatous mitral valve disease (MMVD) is the most common heart disease in dogs. It is characterized by chronic progressive degenerative lesions of the mitral valve. The valve leaflets become thickened and prolapse into the left atrium resulting in mitral regurgitation (MR). MMVD is most prevalent in small to medium sized dog breeds, Cavalier King Charles Spaniels (CKCS) in particular. The onset of MMVD is highly age dependent, and at the age of 10 years, nearly all CKCS are affected. The incidence of a similar disease in humans-mitral valve prolapse-is 1-5%. By defining CKCSs with an early onset of MMVD as cases and old dogs with no or mild signs of MMVD as controls, we conducted a genome-wide association study (GWAS) to identify loci associated with development of MMVD. We have identified a 1.58 Mb region on CFA13 (P(genome) = 4.0 × 10(-5)) and a 1.68 Mb region on CFA14 (P(genome) = 7.9 × 10(-4)) associated with development of MMVD. This confirms the power of using the dog as a model to uncover potential candidate regions involved in the molecular mechanisms behind complex traits.

Hemostatic biomarkers in dogs with chronic congestive heart failure.

BACKGROUND: Chronic congestive heart failure (CHF) in humans is associated with abnormal hemostasis, and abnormalities in hemostatic biomarkers carry a poor prognosis. Alterations in hemostatic pathways can be involved in the pathogenesis of CHF in dogs, and microthrombosis in the myocardium could contribute to increased mortality. HYPOTHESIS: That plasma concentration or activity of hemostatic biomarkers is altered in dogs with CHF and that these factors predict mortality. ANIMALS: Thirty-four dogs with CHF caused by either dilated cardiomyopathy (DCM, n=14) or degenerative valvular disease (CDVD, n=20) compared with 23 healthy age-matched control dogs were included in this study. Dogs with CHF were recruited from 2 referral cardiology clinics, and control dogs were owned by friends or colleagues of the investigators. METHODS: Clinical examination and echocardiography were performed in all dogs. Plasma fibrinogen and D-dimer concentrations, antithrombin and protein C activity, and thrombin-antithrombin complex (TAT) were measured in all dogs. RESULTS: Dogs with CHF had significantly higher fibrinogen (P = .04), D-dimer (P = .002), and TAT concentration (P < .0001), lower antithrombin (P < .0001) and protein C activity (P < .001) compared with control dogs. None of the hemostatic biomarkers were associated with risk of death. CONCLUSIONS AND CLINICAL IMPORTANCE: There is evidence of a procoagulant state in dogs with CHF. The lack of predictive value for survival might be due to the small number of dogs examined. Further studies are necessary to investigate the presence and importance of microthrombosis in dogs with CHF.

Arteriosclerotic changes in the myocardium, lung, and kidney in dogs with chronic congestive heart failure and myxomatous mitral valve disease.

BACKGROUND: The occurrence of small vessel arteriosclerosis in the myocardium, kidney, and lung in dogs with naturally occurring myxomatous mitral valve disease has not been previously investigated systematically. METHODS: Twenty-one dogs with naturally occurring congestive heart failure and 21 age-matched, sex-matched, and weight-matched control dogs underwent extensive pathological and histopathological examination. Morphometry and scoring of tissue sections were used to measure arterial narrowing and fibrosis in the myocardium, kidney, and lung; and intimal thickness and plaque formation in the aorta and pulmonary artery. RESULTS: Dogs with congestive heart failure had significantly more arterial narrowing in the left ventricle (P < .003), lung (P < .0001), and kidney (P < .02); intimal-medial thickening in the pulmonary artery (P = .04); and fibrosis in the left ventricle (P < .0001) than control dogs. However, they did not have more plaque formation or intimal-medial thickening in the aorta than controls. There was significantly more arterial narrowing in papillary muscles than in all other locations in dogs with congestive heart failure (P < .002). In control dogs, arterial changes were less pronounced and did not differ in different locations. CONCLUSIONS: Dogs with naturally occurring myxomatous mitral valve disease have significantly more arterial changes in the myocardium, lung, and kidney, and significantly more fibrosis in the myocardium than control dogs. This could have important implications in the management of myxomatous mitral valve disease and raises interesting questions about the occurrence and importance of intramural small vessel disease in humans with primary mitral valve prolapse.

Circulating concentrations of insulin-like growth factor-1 in dogs with naturally occurring mitral regurgitation.

Insulin-like growth factor-1 (IGF-1), which mediates most effects of growth hormone, has effects on cardiac mass and function, and plays an important role in the regulation of vascular tone. In humans, an inverse relationship between degree of heart failure (HF) and circulating IGF-1 concentrations has been found in several studies. In dogs with HF, few studies have focused on IGF-1. We examined circulating IGF-1 concentrations in dogs with mitral regurgitation (MR) caused by myxomatous mitral valve disease. Study 1 included 88 Cavalier King Charles Spaniels (CKCSs) with a broad range of asymptomatic MR (median serum IGF-1: 76.7 microg/L; 25-75 percentile, 59.8-104.9 microg/L). As expected, standard body weight and percentage under- or overweight correlated directly with IGF-1. MR (assessed in 4 different ways) did not correlate with IGF-1. In study 2, 28 dogs with severe MR and stable, treated congestive HF had similar serum IGF-1 concentrations (median, 100.8 g/L; 25-75 percentile, 74.9-156.5 microg/L) as 11 control dogs (79.6 microg/L; 25-75 percentile, 64.1-187.4 microg/L; P = .84). In study 3, the plasma IGF-1 concentration of 15 untreated CKCSs with severe MR was 16.4 +/- 24.2 microg/L lower (P = .02) at the examination when decompensated HF had developed (80.8 +/- 30.9 microg/L) than at a visit 1-12 months earlier (97.2 +/- 39.8 microg/L), possibly in part due to an altered state of nutrition. The studies document that circulating IGF-1 concentrations are not altered before development of congestive HF in dogs with naturally occurring MR, but decrease by approximately 20% with the development of untreated HE In treated HF, circulating IGF-1 concentrations apparently return to within the reference range.

Dogs with heart diseases causing turbulent high-velocity blood flow have changes in platelet function and von Willebrand factor multimer distribution.

The purpose of this prospective study was to investigate platelet function using in vitro tests based on both high and low shear rates and von Willebrand factor (vWf) multimeric composition in dogs with cardiac disease and turbulent high-velocity blood flow. Client-owned asymptomatic, untreated dogs were divided into 4 groups: 14 Cavalier King Charles Spaniels (Cavaliers) with mitral valve prolapse (MVP) and no or minimal mitral regurgitation (MR), 17 Cavaliers with MVP and moderate to severe MR, 14 control dogs, and 10 dogs with subaortic stenosis (SAS). Clinical examinations and echocardiography were performed in all dogs. PFA100 closure times (the ability of platelets to occlude a hole in a membrane at high shear rates), platelet activation markers (plasma thromboxane B2 concentration, platelet surface P-selectin expression), platelet aggregation (in whole blood and platelet-rich plasma with 3 different agonists), and vWf multimers were analyzed. Cavaliers with moderate to severe MR and dogs with SAS had longer closure times and a lower percentage of the largest vWf multimers than did controls. Maximal aggregation responses were unchanged in dogs with SAS but enhanced in Cavaliers with MVP (regardless of MR status) compared with control dogs. No significant difference in platelet activation markers was found among groups. The data suggest that a form of platelet dysfunction detected at high shear rates was present in dogs with MR and SAS, possibly associated with a qualitative vWf defect. Aggregation results suggest increased platelet reactivity in Cavaliers, but the platelets did not appear to circulate in a preactivated state in either disease.

Efficacy of enalapril for prevention of congestive heart failure in dogs with myxomatous valve disease and asymptomatic mitral regurgitation.

We evaluated the long-term effect of early angiotensin-converting enzyme (ACE) inhibition (enalapril maleate) as monotherapy to postpone or prevent congestive heart failure (CHF) in asymptomatic dogs with mitral regurgitation (MR) attributable to myxomatous valvular disease (MVD) in a prospective, randomized, double-blinded, placebo-controlled multicenter trial involving 14 centers in Scandinavia. Two hundred twenty-nine Cavalier King Charles (CKC) Spaniels with MR attributable to MVD but no signs of CHF were randomly allocated to treatment with enalapril 0.25-0.5 mg daily (n = 116) or to placebo groups (n = 113). Each dog was evaluated by physical examination, electrocardiography, and thoracic radiography at entry and every 12 months (+/-30 days). The number of dogs developing heart failure was similar in the treatment and placebo groups (n = 50 [43%] and n = 48 [42%], respectively; P = .99). The estimated means, adjusted for censored observations, for the period from initiation of therapy to heart failure were 1,150 +/- 50 days for dogs in the treatment group and 1,130 +/- 50 days for dogs in the placebo group (P = .85). When absence or presence of cardiomegaly at the entrance of the trial was considered, there were still no differences between the treatment and placebo groups (P = .98 and .51, respectively). Multivariate analysis showed that enalapril had no significant effect on the time from initiation of therapy to heart failure (P = .86). Long-term treatment with enalapril in asymptomatic dogs with MVD and MR did not delay the onset of heart failure regardless of whether or not cardiomegaly was present at initiation of the study.

Associations between N-terminal procollagen type III, fibrosis and echocardiographic indices in dogs that died due to myxomatous mitral valve disease.

OBJECTIVES: To evaluate associations between N-terminal procollagen type III (PIIINP), a serum biomarker of collagen biosynthesis, and myocardial fibrosis in dogs with naturally-occurring myxomatous mitral valve disease (MMVD). ANIMALS: Twenty-two dogs with echocardiographically-confirmed MMVD were prospectively recruited from a hospital population. All died as a result of MMVD and their hearts were available for post mortem examination. METHODS: Echocardiographic measurements and serum PIIINP concentrations were obtained from all dogs prior to death or euthanasia. Serum PIIINP concentrations (µg/mL) were measured using a validated commercially available radioimmunoassay. Myocardial tissue samples were collected post mortem and myocardial fibrosis was scored. The average fibrosis score for all cardiac sites in the heart was designated the global fibrosis score (GFS). The average fibrosis score for all papillary muscle sites was designated the papillary fibrosis score (PFS). Univariate and multivariate linear regression analyses were used separately to evaluate associations between GFS and PFS, respectively, and PIIINP and echocardiographic variables. RESULTS: Left ventricular end-diastolic diameter normalized for body weight (LVEDDN) and PIIINP were weakly independently positively associated with both GFS and PFS. LVEDDN and PIIINP were weakly negatively correlated. CONCLUSIONS: Both LVEDDN and serum PIIINP increase with increasing fibrosis score, although these relationships were not strong enough to be clinically useful. Although LVEDDN and PIIINP were positively correlated with fibrosis, PIIINP decreased with increasing LVEDDN, suggesting a complex interplay between fibrosis and remodeling in MMVD.

Circulating cytokine concentrations in dogs with different degrees of myxomatous mitral valve disease.

Cytokines have been associated with the progression of congestive heart failure (CHF) in humans and may be implicated in the pathophysiology of myxomatous mitral valve disease (MMVD) in dogs. The aim of this study was to determine the serum concentrations of cytokines in dogs with MMVD. The study included 16 Cairn terriers with no or minimal mitral regurgitation (MR), 41 Cavalier King Charles Spaniels (CKCS) with different degrees of MR and 11 dogs of different breeds with CHF due to MMVD. Granulocyte-macrophage colony-stimulating factor, interferon-γ, interleukin (IL)-2, IL-6, IL-7, IL-8, IL-10, IL-15, IL-18, keratinocyte-derived chemokine, interferon-γ-induced protein and monocyte chemoattractant protein-1 (MCP-1) were measured using a canine-specific multiplex immunoassay. CHF dogs had significantly higher MCP-1 concentrations than dogs with no or minimal MR. Among the CKCS, IL-2 and IL-7 decreased with increasing left atrial size and IL-7 also decreased with increasing MR. IL-8 decreased with increasing left ventricular end-systolic internal dimensions. MCP-1 was increased in CHF dogs compared to healthy control dogs and IL-2, IL-7 and IL-8 decreased with increasing indices of disease severity. The results suggest a role for these cytokines in canine MMVD and CHF.

Brain-natriuretic peptide and cyclic guanosine monophosphate as biomarkers of myxomatous mitral valve disease in dogs.

Elevations in the plasma concentrations of natriuretic peptides correlate with increased severity of myxomatous mitral valve disease (MMVD) in dogs. This study correlates the severity of MMVD with the plasma concentrations of the biomarkers N-terminal fragment of the pro-brain-natriuretic peptide (NT-proBNP) and its second messenger, cyclic guanosine monophosphate (cGMP). Furthermore, the L-arginine:asymmetric dimethylarginine (ADMA) ratio was measured as an index of nitric oxide availability. The study included 75 dogs sub-divided into five groups based on severity of MMVD as assessed by clinical examination and echocardiography. Plasma NT-proBNP and cGMP concentrations increased with increasing valve dysfunction and were significantly elevated in dogs with heart failure. The cGMP:NT-proBNP ratio decreased significantly in dogs with heart failure, suggesting the development of natriuretic peptide resistance. Although the l-arginine:ADMA ratio decreased with increasingly severe MMVD, this was largely due to the older age of the dogs with heart failure.

Associations between cardiac pathology and clinical, echocardiographic and electrocardiographic findings in dogs with chronic congestive heart failure.

The objective of this study was to correlate defined pathological features with clinical findings in dogs with naturally occurring congestive heart failure (CHF). Fifty-eight dogs with CHF were examined clinically and using echocardiography and electrocardiography. Detailed cardiac post-mortem examination was used to assess intra-myocardial arterial narrowing, myocardial fibrosis and atrophy and myxomatous mitral valve degeneration (MMVD). Arterial narrowing significantly correlated with fibrosis (P<0.0001) and with fractional shortening, an indicator of systolic function (P=0.002). The grade of fibrosis was associated with shorter survival time (P=0.002), and the papillary muscle fibrosis score tended to correlate with proximal isovelocity surface area radius (P=0.03). Data from this study lend support to the hypothesis that naturally occurring canine CHF is affected by several factors such as MMVD, myocardial atrophy and fibrosis, and by arteriosclerosis. Further, more extensive research will be required to establish cause-effect relationships between these cardiac lesions and the pathophysiology of CHF in dogs.