Clinical and necropsy evaluation of endocardial fibroelastosis in a mixed-breed cat with left side heart failure.

A two-month-old, male intact, mixed-breed cat weighing 0.6 kg was presented with respiratory distress and anorexia. From the transthoracic echocardiographic, reduced fractional shortening (FS) and increased endocardial echogenicity were recognised with severe congestive heart failure (CHF). The kitten was administered an antibiotic and pimobendane under oxygen supplementation in an ICU cage. However, the respiratory condition worsened and the cat died the next day, and the subsequent necropsy and histopathology examinations confirmed endocardial fibroelastosis (EFE). There is a lack of information regarding the antemortem cardiac function evaluated by tissue Doppler imaging (TDI) in EFE cases. We report on the echocardiographic findings including the TDI in the EFE cat with a concomitant necropsy and histopathology confirmation in this paper. The echocardiographic findings showed presence of a ventricular false tendon within the left ventricle, a decrease in the left ventricular contractility (FS 11.1%, and a marked CHF). In this case, the echocardiographic findings were consistent with the human counterpart. However, these findings were like those of dilated cardiomyopathy and, hence, non-specific to EFE. As a result, veterinarians should keep in mind that endocardial fibroelastosis might be a possible reason for respiratory distress resulting from CHF with a low fractional shortening in young cats.

Increased proportion of apoptotic cells in cat kidney tissues infected with feline morbillivirus.

In order to study potential pathogenic mechanisms of feline morbillivirus (FeMV) in infected kidney cells, we performed a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and an immunofluorescence assay (IFA) with an anti-FeMV P protein antibody on a total of 38 cat kidney tissues, 12 of which were positive for FeMV. Among these samples, we detected significantly larger numbers of apoptotic cells in FeMV-positive tissues than in FeMV-negative tissues, and in these tissues, a substantial percentage of TUNEL-positive (TUNEL+) cells contained the FeMV P protein (mean, 37.4; range, 17.4-82.9), suggesting that induction of apoptosis may be an important mechanism for pathological changes associated with FeMV infection in cat kidney tissues.

Pathology and Proteomics-Based Diagnosis of Localized Light-Chain Amyloidosis in Dogs and Cats.

Amyloidosis is classified according to the amyloid precursor protein, and accurate diagnosis of the amyloidosis type may guide appropriate treatment. Immunohistochemistry and Congo red staining are the most frequently used methods used to distinguish types of amyloidosis, but problems with specificity and sensitivity indicate the need for an alternative diagnostic method. In this study, we evaluated laser microdissection-liquid chromatography-tandem mass spectrometry (LMD-LC-MS/MS) for the diagnosis of amyloid light-chain (AL) amyloidosis in animals. Plasmacytomas with amyloid deposits from 15 dogs and 2 cats were subjected to Congo red staining with or without potassium permanganate pretreatment, immunohistochemistry for kappa and lambda light chains, and LMD-LC-MS/MS. Congo red staining was diagnostic in 12 of 17 cases based on resistance to potassium permanganate pretreatment, but in 5 of 17 cases the pretreatment unexpectedly reduced Congo red staining or abrogated the birefringence and a definitive diagnosis could not be reached. Immunohistochemistry detected kappa or lambda light chains in 6 of 17 cases. With LMD-LC-MS/MS, immunoglobulin lambda light chain was detected in all 17 cases. The amyloid signature proteins ApoA-I, ApoA-IV, and ApoE were detected in 9, 1, and 3 of the 15 canine cases by LMD-LC-MS/MS, but not in the feline cases. In conclusion, LMD-LC-MS/MS consistently determined the amyloid type in all examined specimens, while Congo red staining after potassium permanganate treatment and immunohistochemistry were less sensitive tests.

Long-term outcomes of 54 dogs with tracheal collapse treated with a continuous extraluminal tracheal prosthesis.

OBJECTIVE: To describe the surgical placement of a continuous extraluminal tracheal prosthesis (CETP) and report the subsequent postoperative clinical outcomes in dogs with tracheal collapse. STUDY DESIGN: Retrospective case series. ANIMALS: Fifty-four dogs. METHODS: Medical records of dogs in which cervical and/or thoracic inlet tracheal collapse was diagnosed and treated by placement of a CETP between 2010 and 2017 were reviewed to evaluate postoperative complications, changes in respiratory function, and survival. Histological examinations of tracheal tissues performed in 2 dogs at 51 and 57 months after surgery were also reviewed. RESULTS: Fifty-three (98%) dogs survived to discharge. Postoperative complications included laryngeal paralysis (1 dog), disseminated intravascular coagulation (1 dog), and recurrent tracheal collapse (2 dogs). None of the dogs exhibited clinical evidence of tracheal necrosis. Preoperative dry, harsh cough resolved in 87% of the dogs after surgery. Goose honking cough was resolved in 25 of 26 (96%) dogs. Median follow-up time was 30 months (range, 16 days to 76 months). The survival rate at 36 months was 86% (CI: 75%-96%). On histological examination in 2 dogs, the tracheal tissue surrounding the prosthesis was well preserved and without evidence of chronic inflammation. CONCLUSION: Continuous extraluminal tracheal prosthesis placement in dogs with tracheal collapse resulted in low postoperative complication rates and good long-term outcomes. CLINICAL SIGNIFICANCE: Continuous extraluminal tracheal prosthesis placement provides a viable alternative surgical option for managing dogs with tracheal collapse.

Overexpression of heart-specific small subunit of myosin light chain phosphatase results in heart failure and conduction disturbance.

Mutations in genes encoding components of the sarcomere cause cardiomyopathy, which is often associated with abnormal Ca2+ sensitivity of muscle contraction. We have previously shown that a heart-specific myosin light chain phosphatase small subunit (hHS-M21) increases the Ca2+ sensitivity of muscle contraction. The aim of the present study was to investigate the function of hHS-M21 in vivo and the causative role of abnormal Ca2+ sensitivity in cardiomyopathy. We generated transgenic mice with cardiac-specific overexpression of hHS-M21. We confirmed that hHS-M21 increased the Ca2+ sensitivity of cardiac muscle contraction in vivo, which was not followed by an increased phosphorylation of myosin light chain 2 isoforms. hHS-M21 transgenic mice developed severe systolic dysfunction with myocardial fibrosis and degeneration of cardiomyocytes in association with sinus bradycardia and atrioventricular conduction defect. The contractile dysfunction and cardiac fibrosis were improved by treatment with the Rho kinase inhibitor fasudil. Our findings suggested that the overexpression of hHS-M21 results in cardiac dysfunction and conduction disturbance via non-myosin light chain 2 phosphorylation-dependent regulation. NEW & NOTEWORTHY The present study is the first to develop mice with transgenic overexpression of a heart-specific myosin light chain phosphatase small subunit (hHS-M21) and to examine the effects of hHS-M21 on cardiac function. Elevation of hHS-M21 induced heart failure with myocardial fibrosis and degeneration of cardiomyocytes accompanied by supraventricular arrhythmias.

Evaluation of endothelialization in the center part of graft using 3 cm vascular grafts implanted in the abdominal aortae of the rat.

In order to develop small-diameter vascular grafts, it is necessary to evaluate endothelialization, especially, in the center part at early stage. For implantation of vascular grafts of 1 cm in length to abdominal aortae of rat, endothelial cells can be formed easily by stretching anastomosis. We evaluated the endothelialization in the center part of vascular grafts by implanting vascular grafts using transgenic (TG) silk fibroin (SF) of 3 cm in length. Vascular grafts were prepared 1.5 mm in diameter and 1 and 3 cm in length using wild type (WT) SF and TG SF by braiding structure, respectively. The grafts were removed after 2 weeks or 3 months and evaluated pathologically. Endothelialization was not confirmed totally after 3 months of implantation. However, endothelialization in the center part of grafts was significantly higher in TG SF than in WT SF. No significant difference was found regarding tissue infiltration and internal diameter. The TG SF revealed migration of the endothelial cells into the center part of the vessels at the early stage. Also, tissue infiltration and remodeling is expected using SF. The 3 cm length vascular grafts can be evaluated as a new experimental system.

Molecular basis for clinical heterogeneity in inherited cardiomyopathies due to myopalladin mutations.

Abnormalities in Z-disc proteins cause hypertrophic (HCM), dilated (DCM) and/or restrictive cardiomyopathy (RCM), but disease-causing mechanisms are not fully understood. Myopalladin (MYPN) is a Z-disc protein expressed in striated muscle and functions as a structural, signaling and gene expression regulating molecule in response to muscle stress. MYPN was genetically screened in 900 patients with HCM, DCM and RCM, and disease-causing mechanisms were investigated using comparative immunohistochemical analysis of the patient myocardium and neonatal rat cardiomyocytes expressing mutant MYPN. Cardiac-restricted transgenic (Tg) mice were generated and protein-protein interactions were evaluated. Two nonsense and 13 missense MYPN variants were identified in subjects with DCM, HCM and RCM with the average cardiomyopathy prevalence of 1.66%. Functional studies were performed on two variants (Q529X and Y20C) associated with variable clinical phenotypes. Humans carrying the Y20C-MYPN variant developed HCM or DCM, whereas Q529X-MYPN was found in familial RCM. Disturbed myofibrillogenesis with disruption of α-actinin2, desmin and cardiac ankyrin repeat protein (CARP) was evident in rat cardiomyocytes expressing MYPN(Q529X). Cardiac-restricted MYPN(Y20C) Tg mice developed HCM and disrupted intercalated discs, with disturbed expression of desmin, desmoplakin, connexin43 and vinculin being evident. Failed nuclear translocation and reduced binding of Y20C-MYPN to CARP were demonstrated using in vitro and in vivo systems. MYPN mutations cause various forms of cardiomyopathy via different protein-protein interactions. Q529X-MYPN causes RCM via disturbed myofibrillogenesis, whereas Y20C-MYPN perturbs MYPN nuclear shuttling and leads to abnormal assembly of terminal Z-disc within the cardiac transitional junction and intercalated disc.

Pimobendan improves right ventricular myocardial contraction and attenuates pulmonary arterial hypertension in rats with monocrotaline-induced pulmonary arterial hypertension.

PURPOSE: The present study aimed to evaluate the therapeutic effect of pimobendan treatment for pulmonary hypertension (PH) in rats administered monocrotaline (MCT). METHODS: Fifty-four 12-week-old male Sprague-Dawley rats were injected with monocrotaline or saline solution. Serial echocardiography and right ventricular systolic pressure (RVSP) measurement via a cardiac catheter were performed. After injection of MCT, rats received oral pimobendan (MCT/pimobendan group) or no treatment (MCT group) until undergoing echocardiography and cardiac catheter insertion. RESULTS: Right ventricular systolic pressure in the MCT/pimobendan group was lower than that in the MCT group at 6 weeks. Right ventricle free wall (RVFW) myocardial systolic velocity (Sm) in the MCT group showed a reduction compared with the saline group at 2 weeks. RVFW Sm in the MCT/pimobendan group was preserved as compared with the saline group at 2 weeks. RVFW Tei index in the MCT/pimobendan group showed a reduction compared with the saline group and the MCT group at 2 weeks. Echocardiography in the MCT/pimobendan group showed improvement compared with MCT rats. CONCLUSIONS: Both a reduction in RVSP and improvement in myocardial contraction were demonstrated with administration of pimobendan in rats with PH induced by MCT. Echocardiography evaluation of systolic function seems to be useful for monitoring excess administration of pimobendan.

Pathological features of primary cardiac myxoid tumour in dogs: a review of 11 cases (2002-2022).

This report documents the pathological features of primary cardiac myxoid tumour (MT) in 11 dogs. Macroscopically, all the tumours were located in the tricuspid valve (TV), its septal leaflet being predominantly affected. Therefore, it appears that the TV is the most common site of occurrence for cardiac MT in dogs. Two gross anatomical types of canine valvular MT were evident. Seven of the 11 tumours were round or oval with a smooth or gently lobulated and glistening surface, while the other four were gelatinous, multilobulated and polypoid, with an irregular surface. Microscopically, in nine cases the tumours had an abundant myxoid matrix within which elongated spindle-shaped cells with no remarkable cytological atypia were sparsely embedded, suggesting a benign character (ie, myxoma). In the other two cases the tumours consisted of variably dense, haphazardly arranged, interlacing streams of anaplastic spindle-shaped or polygonal cells containing many mitotic figures, indicative of a malignant form of myxoma (ie, myxosarcoma). Isolated or clustered collections of myxoma cells (eg, cords, rings, syncytia) characteristic of human atrial myxoma were only rarely evident or lacking in all 11 cases, indicating that rarity or absence of such structural features may be specific to valvular MTs. Immunohistochemical findings were indicative of smooth muscle differentiation of the neoplastic cells. Tumour embolization to the intrapulmonary arteries and/or tumour implantation on the endocardium of the right heart chambers was evident only in the four cases of irregular-surfaced MT.

The anatomical basis of third-degree atrioventricular block in dogs with atrioventricular valve endocardiosis.

The cardiac conduction system was examined histologically in 13 canine cases of atrioventricular (AV) valve endocardiosis with third-degree AV block. In all cases, gross examination revealed marked thickening and distortion of the base of the central fibrous body (CFB) and varying degrees of endocardial thickening of the upper portion of the ventricular septum (VS) as well as marked thickening of the mitral and tricuspid valve leaflets due to myxomatous degeneration. Microscopically, the thickened and distorted CFB had encased or trapped, either partly or totally, the underlying penetrating and branching portions of the AV bundle. The myxomatous and/or fibrofatty tissue, which had proliferated at the base of the extensive CFB, protruded into or encroached on the AV bundle, causing severe (51-75%) to very severe (76% or more) reduction of the conduction fibres. The upper portions of the left and right bundle branches were involved in the endocardial thickening due to degenerative and fibrotic changes at the uppermost VS; however, both bundle branches were much less severely affected than the AV bundle, the degree of reduction of the conduction fibres ranging from mild (25% or less) to moderate (26-50%). These observations suggest that the sites most vulnerable to lesions in the AV conduction system are the penetrating and branching portions of the AV bundle, which would represent the anatomical basis for third-degree AV block in canine cases of AV valve endocardiosis.