Metabolic and structural abnormalities in dogs with early left ventricular dysfunction induced by incessant tachycardia

OBJECTIVE: To assess morphologic and metabolic abnormalities in dogs with early left ventricular dysfunction (ELVD) induced by rapid right ventricular pacing (RRVP). ANIMALS: 7 Beagles. PROCEDURE: Plasma carnitine concentrations were measured before and after development of ELVD induced by RRVP. At the same times, transvenous endomyocardial biopsy was performed, and specimens were submitted for determination of myocardial carnitine concentrations and histologic, morphometric, and ultrastructural examination. RESULTS: In 4 dogs in which baseline plasma total carnitine concentration was normal, RRVP induced a decrease in myocardial total and free carnitine concentrations and an increase in myocardial esterified carnitine concentration. In 3 dogs in which baseline plasma total carnitine concentration was low, plasma and myocardial carnitine concentrations were unchanged after pacing. Structural changes associated with pacing included perinuclear vacuolization in 3 dogs. Morphometric analyses indicated there was a decrease in myofiber cross-sectional diameter and area following pacing. Electron microscopy revealed changes in myofibrils and mitochondria following pacing. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that moderate to severe alterations in myocyte cytoarchitecture are present in dogs with ELVD induced by RRVP and that in dogs with normal plasma carnitine concentrations, myocardial carnitine deficiency may be a biochemical marker of ELVD. Results also indicated that transvenous endomyocardial biopsy can be used to evaluate biochemical and structural myocardial changes in dogs with cardiac disease.     

Arrhythmogenic right ventricular cardiomyopathy in a dog

An 8-month-old Labrador retriever bitch was evaluated for sudden-onset, progressive abdominal distension. Physical examination revealed an exaggerated inspiratory effort, severe ascites, bilateral jugular vein distension, and hypokinetic femoral arterial pulses. Thoracic auscultation detected tachycardia with muffled heart sounds, without audible cardiac murmurs. Thoracic radiographs identified severe right ventricular enlargement and pleural effusion. The electrocardiogram was consistent with incomplete right bundle branch block or right ventricular enlargement. Echocardiography demonstrated severe right ventricular and atrial dilation, secondary tricuspid regurgitation, and thinning and hypocontractility of the right ventricular myocardium. Left heart chamber sizes were slightly decreased, with normal left ventricular contractility. A diagnosis of arrhythmogenic right ventricular cardiomyopathy was reached, based on the characteristic clinical, electrocardiographic, radiographic and echocardiographic findings, and the exclusion of other causes of isolated right ventricular failure. Treatment effected good control of clinical signs, until acutely decompensated congestive right heart failure led to euthanasia after 4 months. Arrhythmogenic right ventricular cardiomyopathy is a well-described clinical entity in humans, and has previously been documented in 3 male dogs. The condition is characterised by progressive fibro-adipose replacement of right ventricular myocardium, while the left ventricle usually remains unaffected. It should be considered a differential diagnosis in any young dog presented with isolated right heart failure, syncope, or unexplained ventricular tachyarrhythmias. This article reports the 1st case of arrhythmogenic right ventricular cardiomyopathy in a female dog, and highlights its echocardiographic features.     

Endomyocardial fibrosis and restrictive cardiomyopathy: pathologic and clinical features

Restrictive cardiomyopathy (RCM) is a primary myocardial disorder characterized by diastolic dysfunction and wide phenotypic heterogeneity. Clinicopathologic features in cats are currently poorly defined. One form of RCM is associated with endomyocardial fibrosis. The hallmark feature of endomyocardial fibrosis RCM is severe endomyocardial scar that may diffusely involve the left ventricle, or appear as a distinct lesion bridging the ventricular septum and left ventricular free wall. In some cases this may reduce left ventricular chamber volume or result in apical or mid chamber stenosis with associated pressure gradients. Left atrial enlargement is generally severe. Ventricular hypertrophy is variable and is often associated with wall or chamber remodeling. Histopathologic features include striking endocardial scar, myocardial interstitial fibrosis, and in some instances, endomyocarditis.     

Left ventricular outflow tract obstruction caused by a congenital accessory mitral valve leaflet and treated by open-heart surgery in a young dog

A 3-month-old Shetland sheepdog presented with a loud ejection murmur and exercise intolerance. Echocardiography revealed an accessory mitral valve leaflet, characterised by a valve-like structure separate from the mitral valve seen in the subaortic region of the ventricular septum. The left ventricular outflow tract was partially obstructed with a pressure gradient of 12 mmHg. Accessory mitral valve leaflet resection and mitral valvuloplasty were performed during open-heart surgery. Histology performed on the membrane-like structures were indicative of fibrous connective tissues. Postoperative echocardiography confirmed removal of the valve-like structure with resolution of the left ventricular outflow tract obstruction. The pressure gradient was decreased to 4.6 mmHg. The dog was in good condition and no further treatment was required 5 months after surgery. Both cardiac troponin I and NT-proBNP were markedly decreased. In this dog, surgical resection combined with mitral valve plasty resolved the left ventricular outflow tract obstruction and the clinical signs.     

Ultrasound-guided serial transabdominal cardiac biopsies in cats

A percutaneous/transdiaphragmatic core needle biopsy technique was developed in cats to obtain serial biopsies from different locations of the left ventricle, through which morphological and molecular changes within the same individual can be studied to unravel the mechanisms of feline cardiomyopathies. Transmural left ventricular myocardial samples were obtained from 29 anesthetized, healthy, adult cats with ultrasound guidance. An 18G automatic biopsy needle was inserted between the last left rib and the sternum through the diaphragm into the thorax. Biopsies were obtained from the left ventricular wall. In five cats, three single biopsies were taken with 4-week intervals. Autopsy was performed on six cats, of which three cats had serial biopsies. In total, 87 biopsies were obtained without long-term effects on cardiac function or structure. The biopsies caused transient single ventricular premature complexes and mild pericardial effusion without tamponade. Necropsy revealed a minimal amount of fibrous connective tissue in the diaphragm and the heart without any significant microscopic lesions in the adjacent muscle tissue. The high quality biopsy material was suitable for morphological and molecular studies. This minimally invasive, ultrasound-guided cardiac biopsy technique thus allows for the safe collection of serial biopsies to study feline cardiomyopathies in an experimental setting.     

Arrhythmogenic right ventricular cardiomyopathy in two cats

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a disease characterised by infiltration of the myocardium by adipose and fibrous tissue. The disease is an important cause of sudden death in humans, but has rarely been described in animals. This report describes ARVC in two cats with right-sided congestive heart failure. One cat had also experienced previous episodes of syncope. Standard six-lead and 24-hour (Holter) electrocardiogram recording revealed complete atrioventricular block and multiform ventricular ectopics in both cats, with the addition of ventricular tachycardia, ventricular bigeminy and R-on-T phenomenon in one of them. On echocardiography, the right ventricle and atrium were massively dilated and hypokinetic. The survival times of the cats were three days and 16 days following diagnosis. Histopathology in one case revealed fibro-fatty infiltration of the myocardium, predominantly affecting the right ventricular free wall.     

COMPARISON OF ECHOCARDIOGRAPHY-GUIDED AND FLUOROSCOPY-GUIDED ENDOMYOCARDIAL BIOPSY TECHNIQUES

The accuracy of bioptome placement for endomyocardial biopsy was evaluated using standard fluoroscopic guidance and compared simultaneously with two-dimensional echocardiography in six healthy subadult grizzly bears (Ursus arctos horribilis). Despite perceived adequate positioning of the bioptome toward the septum when judged using fluoroscopy, only one out of the six placements were actually positioned in the right ventricular apex toward the septum when evaluated using two-dimensional echocardiography. The bioptome was readily relocated to the right ventricular apex/septal location by echocardiography. The forceps were easily visualized at all times and the open cups were readily directed into the desired location for biopsy. Based on a subjective score for tissue quantity from 1 to 4 (poor to excellent), biopsies collected by echocardiographic-guided technique had a mean score of 3.4, while biopsies collected by fluoroscopic-guided technique had a mean score of 1.8. In summary, this study suggests that endomyocardial biopsy locations can be accurately positioned using two-dimensional echocardiography with the advantages of less radiation, lower procedural costs, and direct visualization of the sampling site. Clear definition of endocardial surface as afforded by echocardiography may enhance tissue sample quality and lower potential complications from this procedure.     

Modified transvenous endomyocardial biopsy technique in dogs

A technique for transvenous endomyocardial biopsy of the right ventricle was developed and evaluated for safety and efficacy in healthy dogs and dogs with dilated cardiomyopathy positioned in lateral recumbency. This technique allowed acquisition of multiple biopsy specimens from the right ventricle of each of 22 hemodynamically normal dogs and 40 of 42 dogs with congestive heart failure. In 2 dogs with dilated cardiomyopathy, transvenous access to the right ventricle could not be achieved, but left ventricular biopsy was performed without complication. Complications were infrequent, and dogs recovered to at least their baseline status within 48 hours. Evaluation of the efficacy and complication rate of the procedure with each of the 2 biopsy instruments currently available identified no differences between them.     

Primary sinonasal malignant melanoma with systemic metastasis in a non-gray horse

A 27-y-old Anglo-Arabian gelding with bay coat color was presented with a swelling of the left maxillary region. Fenestration on the left maxilla revealed that the left maxillary sinus was filled with black-red tissue. A portion of the tissue was excised and diagnosed histologically as malignant melanoma. Genotyping of the STX17 gene for gray coat color revealed that the horse did not have the “gray” factor. The horse was euthanized ~3 mo after first presentation. During autopsy, a black-to-gray mass extended from the left nasal cavity to the surrounding paranasal sinus and invaded the hard palate, cribriform plate, and the cranial portion of the left olfactory bulb. Moreover, identical black nodules were present in lymph nodes from the mandible to the larynx, and in the spleen, liver, kidney, and adrenal glands. However, masses were not found in the skin, perineal region, or pelvic cavity. All of the black-to-gray nodules were malignant melanomas that were histologically identical to the initial biopsy; tumor emboli were also found in the kidney. Sinonasal mucosal melanoma is a rare disease in horses.     

Giant cell tumor of the bone in a scarlet macaw (Ara macao)

A 6-mo-old female scarlet macaw (Ara macao) was presented after a 2-mo period of anorexia and weakness. The bird was reluctant to fly 1 wk before referral due to a painful left wing. Physical examination revealed a firm swelling around the left shoulder. On radiographs, the diaphysis and proximal metaphysis of the left scapula were radiolucent. Computer tomography revealed an osteolytic process, suggestive of a bone tumor, affecting the left scapula. Cytology of a fine needle aspiration biopsy of the mass showed erythrocytes, a proliferation of spindle-shaped mesenchymal cells, and multinucleated giant cells (osteoclasts) suggestive of a giant cell tumor. The left wing, including the scapula, was amputated. The bird showed a fast recovery but died 1 hr later. Findings during the pathological examination were compatible with shock due to blood loss. The shoulder process was characterized as a giant cell tumor. To our knowledge, this is the first complete report of a giant cell tumor of the bone in a bird.     

Permanent Pacemaker Implantation for Treatment of Symptomatic Bradycardia in Two Cats

Two cats with bradycardia and syncope were treated by permanent pacemaker implantation. Cat 1 had multiple episodes of syncope intermittently over a 10-month period and then multiple episodes within 24 hours; cat 2 had episodes of collapse over a 3-month period. Clinical signs included disorientation, vocalization, and collapse. High-grade second-degree AV block was recorded in both cats, with left and right bundle branch block in cat 1 and right bundle branch block in cat 2. Neither responded to pharmacologic therapy. In cat 1, an epimyocardial electrode was implanted into the left ventricular apex by a ventral abdominal transdiaphragmatic surgical approach. Cat 2 had a permanent smooth endocardial pacing lead introduced into the fight external jugular vein and directed into the right ventricular apex. Both cats were clinically normal within three days after implantation. Complications in cat 2 included failure of pacemaker capture, endocardial lead dislodgement, and pulse generator pocket seroma. Cats with symptomatic bradycardia caused by second-degree and third-degree AV block can be effectively treated by pacemaker implantation by surgical endomyocardial or perivenous endocardial lead placement.     

Spontaneous Cardiac Hypertrophy in a Crl:CD(SD) Rat

Cardiac hypertrophy was observed in a 9-week-old Crl:CD(SD) rat that died unexpectedly. The animal was allocated to the control group of a toxicity study, and no abnormalities in its general conditions, body weight or food intake were observed. Necropsy revealed an increase in heart weight. Gross examination indicated cardiac enlargement with thickening of the right and left ventricular walls. Histopathological examination revealed hypertrophy of the cardiomyocytes in the right and left ventricular walls and the interventricular septum. Electron microscopic examination indicated bizarre nuclei and accumulation of an increased number of various sizes of mitochondria in the perinuclear region of the hypertrophied myocytes. Hypertrophied myocytes connected by intensely folded intercalated disks were also observed. Based on these findings, the animal was diagnosed with cardiac hypertrophy. This is the first case report of cardiac hypertrophy in this strain.     

Congenital supravalvular aortic stenosis in a kitten

A three-month-old, male intact Norwegian forest cat without any clinical signs was referred to the cardiology service of the author’s teaching hospital for evaluation of a cardiac murmur. The murmur was systolic with an intensity of 4 out of 6 with the point of maximal intensity at the left heart base. Echocardiography revealed a moderate mitral valve regurgitation and a moderate dynamic left ventricular outflow tract obstruction both resulting from systolic anterior motion of the mitral valve (SAM). Moreover, left ventricular concentric hypertrophy was noted. Oral atenolol therapy was initiated. Recheck examination 3.5 months later revealed unchanged murmur characteristics in the still asymptomatic kitten. Echocardiography showed no SAM, but there was a severe fixed aortic stenosis apparent caused by a discrete supravalvular lesion, 4 mm distal to the valve, with an hourglass morphology. Supravalvular aortic stenosis is a rare congenital anomaly in cats, which has not been reported antemortem yet.     

Arrhythmogenic right ventricular dysplasia/cardiomyopathy in a Siberian husky

A seven-month-old male Siberian husky was presented with a recent history of anorexia, hindlimb weakness and syncope. Physical examination revealed severe tachycardia, tachypnoea and dyspnoea. Mucous membranes were pale and femoral pulses were weak. An electrocardiogram showed sustained ventricular tachycardia with a left bundle branch block configuration. Thoracic radiographs revealed slight right ventricular enlargement and two-dimensional echocardiography revealed mild right ventricular dilation at the cardiac apex and some hyperechogenic areas on the right side of the interventricular septum. Administration of intravenous lignocaine converted the ventricular tachycardia to sinus rhythm. The maintenance antiarrhythmic therapy consisted of oral procainamide and propranolol. Three weeks later the dog died suddenly. On postmortem examination, the right ventricular free wall was very thin at the apex, infundibulum and caudal aspect of the right ventricular parietal wall, similar to the 'triangle of dysplasia' of human patients. Histopathological examination revealed replacement of several areas of right ventricular free wall myocardium with connective tissue and fat. The right atrium and left ventricle were less severely affected by the same lesions. The clinical and pathological findings are similar to those reported in young people with arrhythmogenic right ventricular dysplasia/cardiomyopathy.     

Clinical evaluation of left ventricular moderator band in 12 dogs

We retrospectively examined clinical data for 12 dogs in which echocardiography revealed the presence of left ventricular moderator bands (LMB). Physical examinations, electrocardiography and echocardiography revealed slight cardiac murmurs, increasing QRS complex and left ventricular turbulent flow (6 of the dogs), respectively. No differences were observed with respect to gender, and no specific clinical symptoms or types of dog that frequently develop this disorder were found.     

A case of papillary squamous cell carcinoma in the mandible of a young French bulldog

A 7-month-old castrated French bulldog was presented with a left-sided mandibular tumor. The initial tumor biopsy diagnosis was ameloblastoma. The owner brought this dog the Kitasato University Veterinary Teaching Hospital for more detailed examination and treatment. Computed tomography revealed a tumor on the left lateral mandibular gingiva from the caudal third of the incisor tooth to the right canine tooth, associated with severe amorphous osteolysis of the mandibular bone. The tumor was surgically excised and diagnosed as papillary squamous cell carcinoma. Currently, 2514 d (6.9 y) since the operation, the dog is healthy, without recurrence.Key clinical message:Although papillary squamous cell carcinoma is rare, many cases have been reported in the oral cavity of medium-to large-sized dogs. Based on this report, papillary squamous cell carcinoma can occur in small dogs such as young French bulldogs and a good prognosis can be achieved with proper resection.     

Cardiomyopathy associated with angiomatous pheochromocytoma in a rhesus macaque (Macaca mulatta)

A 24-year-old female rhesus macaque (Macaca mulatta) presented with a clinical history of chronic heart disease and prolonged recovery from sedation and anesthesia. At necropsy, the heart was markedly enlarged, with thinned ventricular walls, dilated chambers, and severe left atrioventricular valvular insufficiency. The ventricular walls contained numerous narrow, pale, often coalescing streaks that often extended along vessels into the deeper myocardium. Histologically, bands of interstitial fibrosis in the heart were associated with areas of myofiber atrophy, myofibril degeneration and loss, and inflammation. The left adrenal gland contained a 2 x 1 x 0.5 cm tumor with an unusual angiomatous pattern consisting largely of blood-filled sinusoids lined by one to four layers of low cuboidal to polyhedral tumor cells. In most sinusoids, the tumor cells appeared to be in direct contact with blood, although endothelial cells lined some sinusoids. Ultrastructurally, the tumor cells contained abundant electron-dense cytoplasmic granules. These granules were argyrophilic by Sevier-Munger staining and intensely immunoreactive for synaptophysin, chromogranin A, neuron-specific enolase, and S-100. These findings helped confirm the diagnosis of angiomatous pheochromocytoma. The heart lesions match those reported for catecholamine cardiomyopathy in other species.     

Partial anomalous pulmonary venous connection in a dog

A 2-year-old male intact Belgian Malinois was presented for exercise intolerance. A grade III/VI left basilar systolic murmur was detected. Echocardiography revealed moderate right atrial and ventricular dilation and increased pulmonic outflow velocity. Thoracic radiographs showed right heart enlargement and a dilated caudal vena cava. In addition, on the left lateral projection, an enlarged aberrant right cranial pulmonary lobar vein was suspected to be diverging ventrally from the course of the right cranial lobar bronchus and inserting more ventrally than normal in the region of the right atrium. A left-to-right pulmonary vascular shunt was suspected, and the patient underwent further diagnostics under general anesthesia. An agitated saline study was positive, suggestive of a concurrent right to left shunt. A right heart catheterization was performed. Angiography was inconclusive. Oximetry testing revealed an increase in oxygen saturation within the right atrium at the level of the caudal cava supportive of a left-to-right shunt in this region. Computed tomography angiography revealed a large single pulmonary vein that anomalously entered into the caudolateral aspect of the right atrium (left-to-right shunt) and was suspicious for a small arteriovenous malformation between the right caudal pulmonary artery and the right pulmonary vein returning to the left atrium (right to left shunt). The patient was diagnosed with a partial anomalous pulmonary venous connection and a possible arteriovenous malformation.     

Vestibular syndrome associated with an ependymoma in a cat

An ependymoma was diagnosed in a 4.5-year-old spayed Siamese cat with clinical signs of vestibular disease. Diagnosis was based on history, results of neurologic examination, and the finding of neoplastic cells in CSF. Necropsy revealed an ependymoma arising from the fourth ventricle of the ventricular CNS and involving the left medullary and cerebellar areas.