Advances in feline cardiomyopathy

Comparison of echocardiography, biomarkers and taurine concentrations in cats eating high- or low-pulse diets

OBJECTIVES

There are ongoing investigations into diet-associated dilated cardiomyopathy in dogs, but there has been minimal investigation into possible diet-associated dilated cardiomyopathy in cats. The objective of this study was to compare cardiac size and function, cardiac biomarkers and taurine concentrations in healthy cats eating high- vs low-pulse diets. We hypothesized that cats eating high-pulse diets would have larger hearts, lower systolic function and higher biomarker concentrations than cats eating low-pulse diets and that there would be no difference in taurine concentrations between the diet groups.

METHODS

Echocardiographic measurements, cardiac biomarkers, and plasma and whole-blood taurine concentrations were compared between cats eating high- and low-pulse commercial dry diets in a cross-sectional study.

RESULTS

There were no differences between the high- (n = 21) and low-pulse (n = 31) diet groups with regard to age, sex and breed, but more cats in the high-pulse group were overweight or obese (67% vs 39%; P = 0.05). Diet duration was not different in the groups, but the range was wide (6-120 months). No differences were found between the diet groups for key cardiac measurements, biomarker concentrations, or plasma or whole-blood taurine concentrations. However, there were significant negative correlations between diet duration and measures of left ventricular wall thickness in the high-pulse, but not the low-pulse, diet group.

CONCLUSIONS AND RELEVANCE

This study did not detect significant associations between high-pulse diets and cardiac size, function and biomarkers, but the secondary observation of significant negative correlations between time on high-pulse diets and left ventricular wall thickness warrants further evaluation.

Pathological Features and Pathogenesis of the Endomyocardial Form of Restrictive Cardiomyopathy in Cats

This study reports pathological and molecular features in 41 cases of feline restrictive cardiomyopathy (RCM). Grossly, there were patchy or diffuse areas of endocardial thickening affecting the left ventricle. The more common patchy endocardial lesions occurred as large trabecular or irregular broad bands of fibrous tissue bridging the left ventricular free wall and ventricular septum. Microscopically, regardless of the gross pattern, the thickened endocardium contained various numbers of stellate, spindle-shaped or elongated mesenchymal cells surrounded by fibrous connective tissue. Immunohistochemical findings were indicative of smooth muscle differentiation in mesenchymal cells. These cells proliferated vigorously and produced alcian blue-positive ground substance and collagen fibres; it was considered that the mesenchymal cells contributed to the formation of the endocardial lesions. In addition, multiple left ventricular ‘false tendons’ were invariably included within the trabecular or broad fibrous bands, providing a framework for formation of those bands. Evidence of endocarditis or endomyocarditis was lacking in all 41 cases, and no viral genomes were detected in any of the DNA or RNA samples obtained from 14 of the hearts. These observations suggest that any relationship between feline RCM and a virus-induced inflammatory response seems unlikely.

Stimulation of the renin-angiotensin system in cats with hypertrophic cardiomyopathy

Feline hypertrophic cardiomyopathy (HCM) is a disease of the ventricular myocardium, which may cause sudden death in cats, but neither the aetiology nor the effect on the circulation are well understood. Fourteen cats of either sex with naturally occurring HCM were studied post mortem. Their ages ranged from 9 months to 10 years with an average age of 4.9 years. Heart weights and heart weight expressed as a percentage of body weight were elevated (27.9 g and 0.65%, respectively) as compared with normal values obtained in previous studies. Myocardial disarray was evident in nine of the 14 cats and moderate to severe fibrosis was present in six animals. To evaluate the renal renin-angiotensin system, semiquantitative morphometric data were obtained by means of renin immunohistochemistry and compared with results from an earlier study of 10 healthy cats by the author. The juxtaglomerular index was 36.8% in the cats with HCM as compared with 30.6% in healthy cats. The renin-positive portion of the afferent arteriole was increased in cats affected by HCM to 86.0 microm as compared with 49.9 microm in normal cats. The increase in kidney renin values in cats with HCM may have been due to decreased blood pressure and reduced renal perfusion resulting from impaired cardiac output.

Feline distal aortic thromboembolism: a review of 44 cases (1990-1998)

The clinical case records of 44 cats with distal aortic thromboembolism were reviewed. These detailed 49 separate episodes of thromboembolism. Of the 44 cats, 33 (75%) were neutered males, and 43 (98%) were domestic shorthairs. The mean age was 8.7 years (age range 2-16 years). Evidence of pre-existing heart disease had been noted in 23% of cases. Heart failure was a concurrent diagnosis in 51% of episodes and 36% of these cases survived their thromboembolic episodes. Overall, cats survived 39% of the episodes. Cats died during 28% of the episodes, while 33% of the episodes resulted in the cats being euthanased. The median survival time was 6 months. Seventeen per cent of cats on prophylactic aspirin therapy experienced an episode of re-embolisation. Forty-three per cent of episodes occurred in the spring.

Antithrombotic and fibrinolytic factors. A review

Excessive or nonphysiologic thrombogenesis and fibrinolysis accompanies many diseases. Several specific proteins involved in the physiologic regulation and maintenance of blood in a fluid state are reviewed in this article. Assays for these proteins or evidence of their function (antithrombin III, protein C, protein S, plasminogen/plasmin, tissue plasminogen activator, plasminogen activator inhibitor I, fibrinogen/fibrin degradation products, and thrombin/antithrombin complexes) are described. Principles, general methodology, and application in veterinary medicine are discussed. Although most of the investigative work and knowledge concerning these proteins and assays has been in human beings, their use and application in veterinary medicine is becoming more available in research laboratories at referral centers and some larger commercial veterinary laboratories. Use and interpretation of these assays will help clinicians and researchers better understand pathophysiologic processes occurring in various diseases associated with thrombogenesis and excessive fibrinolysis.

Evidence for genetic involvement in feline dilated cardiomyopathy

Quantitative genetic evaluation of clinical dilated cardiomyopathy (DCM) was conducted in a large cattery with known history. Data showed that clinically affected cats were significantly more interrelated than randomly chosen case-control populations from the same colony. The results of this study suggest that quantitative inheritance, either interactive with or independent of nutrition or presently unknown factors, is involved in feline dilated cardiomyopathy.

Myocardial damage in cats that died after anaesthesia

The necropsy findings of 85 cats that died up to six weeks after administration of injectable anaesthetics are described. The most obvious findings in these cats were degeneration and necrosis of heart muscle fibres followed and related to time after the administration of the anaesthetics, by infiltration of predominantly mononuclear cells and by an increase in collagenous connective tissue. The lesions were most obvious on the inner side of the myocardium, indicating that hypoxic injury occurred during anaesthesia. The possible mechanism of the damage to the heart and its role in the pathogenesis of cardiomyopathy in the cat is discussed.

Feline aortic thromboemboli and the potential utility of thrombolytic therapy with tissue plasminogen activator

Feline aortic thromboembolism is a common and devastating clinical condition for which there is presently no effective therapy. Thrombolytic therapy with tissue plasminogen activator represents a promising, relatively noninvasive method for resolution of the clinical syndrome. In clinical trials in man, tissue plasminogen activator is proving to have advantages over previously available thrombolytic agents. Previously available thrombolytic agents require intensive monitoring and commonly cause complications that entail large monetary and manpower costs to monitor and control. Being specific for thrombus-associated plasminogen, t-PA enables more safe and effective thrombolysis without the hazards previously associated with thrombolytic therapy. In cats with aortic thromboemboli, early clinical trials are promising with regard to acute thrombolytic efficacy but raise questions concerning the risks and benefits of therapy and will require more controlled studies. It is estimated that t-PA therapy for a cat with aortic thromboemboli will cost approximately +500 to +1500, including hospitalization and drugs. This compares favorably with what most veterinary clients are willing to spend for quality veterinary care. However, before we can look upon t-PA therapy as a useful therapeutic advance, we must consider the etiopathogenesis and probability of rethrombosis. The results of controlled studies have not been published, but it is generally considered that there is a high probability of recurrence in cats. Fifty per cent of cats treated with t-PA have rethrombosed despite aspirin therapy at the recommended dose of 25 mg per kg every third day. Finding a cure for feline myocardial diseases (cardiomyopathies) and/or an effective method for safely anticoagulating cats at risk would help justify the monetary and manpower costs associated with thrombolytic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet aggregation in feline cardiomyopathy

Platelet aggregation in response to adenosine diphosphate (ADP) was evaluated in 16 healthy cats and in 10 cats with cardiomyopathy. The minimum threshold concentration of ADP required to induce irreversible (2nd-phase) aggregation was determined in each cat. The minimum ADP concentration needed for 2nd-phase aggregation in platelets from healthy cats ranged from 1 microM to 100 microM ADP, with 56% (9/16) requiring 100 microM ADP. Of the remaining seven normal cats, three had platelets responding irreversibly to 10 microM ADP, and four had platelets responding to 1 microM ADP. In cats with cardiomyopathy, the threshold concentrations ranged from 0.01 microM ADP to 10 microM ADP. Two cats had platelets responding irreversibly to 0.01 microM ADP, whereas another cat had a threshold response at 0.1 microM ADP. Platelets from the remaining seven cats with cardiomyopathy exhibited 2nd-phase aggregation in response to 1 microM ADP (five cats) or 10 microM ADP (two cats). Platelet counts ranged from 210,000/mm3 to 630,000/mm3 in healthy cats and from 218,000/mm3 to 624,000/mm3 in cats with cardiomyopathy. There was no apparent correlation between the platelet count and the magnitude of the threshold aggregation response, as measured by lag phase and slope of the aggregation curves. The results indicate that some cats with cardiomyopathy have platelets that are hyperaggregable to ADP in vitro.