Ventricular dyssynchrony as a cause of structural disease in the heart of Dorper sheep

Ventricular dyssynchrony is a disturbance of the normal, organized electromechanical coupling of the two ventricles. This condition has many causes, such as left bundle branch block, ventricular preexcitation, right ventricular pacing and right ventricular premature ventricular complexes (PVCs). Ventricular dyssynchrony has many adverse haemodynamic effects on the left ventricle and we wanted to know whether these adverse haemodynamic effects might have any structural consequences on the left ventricles of such hearts. Six healthy Dorper wethers were subjected to numerous right ventricular PVCs to induce ventricular dyssynchrony in order to determine whether any structural consequences will occur in the left ventricles of these hearts. Myocarditis in the musculature of the left ventricles of all six these hearts was seen.     

Multiple ventricular bands and the associated trabecula septomarginalis dextra in the right ventricle of the domestic dog (Canis familiaris)

Ventricular bands are strand‐like intraventricular structures extending between adjacent papillary muscles; a papillary muscle and the ventricular wall or the interventricular septum and ventricular wall. Examination of the domestic dog right ventricle documented six ventricular band types. Eighty‐five of the 89 examined hearts had at least one right ventricular band. In the current study, the right ventricle of the 85 dog hearts was re‐examined for more than one ventricular band type. Seven patterns of multiple different bands were identified in the 24 dog hearts. The patterns (i.e., combinations) of different ventricular bands were grouped into three categories. Category 1 had five different patterns of bands. Each pattern had two different band types. Category 2 had one combination of three different bands. Category 3 had one combination of four different bands. The presence of right ventricular bands around the trabecula septomarginalis dextra was also documented. All 24 dog hearts with multiple ventricular bands had a trabecula septomarginalis dextra. The main goal of this study was documentation of multiple right ventricular band patterns. A secondary goal was documentation of the combined presence of these bands and a trabecula septomarginalis dextra. In the dog, the ventricular bands and trabecula are both thin, strand‐like intraventricular structures with variable branching patterns before blending into the ventricular wall. The gross similarity of these structures and lack of information on their combined presence could precipitate their misidentification.     

Electrocardiographic surrogates of structural myocardial alterations in the Dorper sheep heart

In this study we evaluated the validity of well-known human electrocardiographic markers of myocardial pathology in Dorper sheep. These markers include: the duration of the QRS complex of premature ventricular complexes (PVCs), the presence of notching of the QRS complex of PVCs and change of the ST-segment of PVCs. It was shown that these three electrocardiographic phenomena correlate with myocardial pathology in the hearts of Dorper sheep. We also describe a new electrocardiographic indicator of myocardial pathology, namely an increase in the frequency of cardiac memory T waves as a new electrocardiographic surrogate for myocardial pathology in the hearts of Dorper sheep.     

Pathological features of arrhythmogenic right ventricular cardiomyopathy in middle-aged dogs

The hearts of four dogs (a 4-year-old Shetland sheepdog, a 4-year-old Labrador retriever, a 5-year-old English Bulldog, and a 6-year-old Dalmatian; three males and one female), that had died suddenly and had been clinically diagnosed as having arrhythmogenic right ventricular cardiomyopathy (ARVC), were studied post mortem. At the cut surface, all four hearts showed mild to moderate hypertrophy of the left and right ventricular free walls and ventricular septum, with grayish-white tissue replacement of the myocardium to various degrees. Histologically, all had typical right ventricular features of ARVC and morphological evidence of left ventricular and ventricular septal involvement. Two main histological patterns were identified: a fatty type (two cases) and a fibrofatty type (two cases). With either type, myocardial replacement by fatty or fibrofatty tissue were detected in both ventricles, but were more severe in the right ventricle, where they usually became transmural. Furthermore, this myocardial replacement was more severely seen in the epimyocardium and midmyocardium; the endomyocardium was less severely affected. On the basis of the present observation, it is evident that, in dogs, the disease process of ARVC affects both the right and left ventricles, although the striking pathological feature is right ventricular involvement. The pathological evidence of biventricular involvement in these canine cases of ARVC may represent a wider spectrum of the disease than has previously been recognized, suggesting that, in dogs, this disease should no longer be considered as limited to the right ventricle.     

A quantitative study of cardiac ventricular mass in dogs.

This study was undertaken to determine the correlations between heart weight, ventricular weight and body weight in adult dogs. A total of 130 dogs was selected for the study after necropsy and histological examination. The body weights (BW) were obtained and a standardized dissection technique was used to obtain the total heart weight (HW), total ventricular mass (VW), right ventricular mass (RvW) and the left ventricular plus the interventricular septum mass (Lv + SW). A strong and significant correlation was found between all variables (BW, HW, VW, Lv + SW and RvW). The following ratios were calculated: HW/BW, RvW/BW, Lv + SW/BW, RvW/VW, Lv + SW/VW, RvW/HW, Lv + SW/HW and Lv + SW/RvW. No sex effect was observed on any ratios. A straight linear relationship was observed between HW and Lv + SW or RvW and between Lv + SW and RvW. The ratios Lv + SW/HW, RvW/HW and Lv + SW/RvW could then be used to predict a normal value of Lv + SW or RvW from a known HW value, or a normal value of Lv + SW from a known RvW value. The relations between BW and HW, Lv + SW or RvW were best described by second order equations. Such equations should be utilized to predict a normal value of HW, Lv + SW or RvW from a known BW value.     

Age‐ and Gender‐Dependent Changes of Bovine Myocardium Architecture

Growth, gravidity and lactation put high demands on the performance of the myocardium. The aim of this study, which was performed in 40 female and 20 male bovines ranging from 1 to 4.5 years old, was to determine gross and microscopic morphometric data of bovine myocardium to establish a comparative measure of myocardial growth during juvenile development. During the developmental stage of young adulthood, age‐related increases in female myocardial characteristics included cardiac mass, left and right ventricular mass and the ratio of cardiac mass to loose connective tissue. Age‐related decreases were observed in the number of myocyte nuclei per mm² and the thickness of the right ventricular wall. Sex differences in these parameters were found between 2‐year‐old bulls (N = 20) and 2‐year‐old heifers (N = 10), with males having heavier hearts, thicker ventricular walls, less myocytes in the left ventricle and less connective tissue in both ventricles. Age and sex had no influence on the ratio of capillaries to myocytes, estimated at 0.98 in the adult bovine. Capillary density does not change during juvenile development, but cross‐sectional capillary area does adapt to myocyte cross‐sectional area, accounting for this relatively constant ratio.     

Swine Hearts: Quantitative Anatomy of the Right Ventricle

The right ventricle was studied in 75 anatomically normal swine hearts, using, in all, nine geometric and volumetric parameters: ventricular-wall thickness, length of the right-ventricular inflow and outflow tracts, and volume of the right-ventricular inflow and outflow tracts. The data for these parameters were compared with previously published patterns for human hearts and volumetric data were compared with patterns of normality found in human hearts. As in the human heart, the ventricular inflow tract in swine hearts was significantly shorter than the outflow tract (P < 0.0001).     

A genome-wide analysis of cardiac lesions of pigs that die during transport: Is heart failure of in-transit-loss pigs associated with a heritable cardiomyopathy?

While heart failure is a primary cause of death for many in-transit-loss (ITL) pigs, the underlying cause of these deaths is not known. Cardiomyopathies are considered a common cause of heart failure in humans and often have a genetic component. The objective of this study was to determine if genes associated with cardiomyopathies could be identified in ITL pigs. Samples from the hearts of pigs that died during transport to an abattoir in Ontario, Canada were collected and genotyped along with samples from pigs that did not die during transport (ILT hearts: n = 149; non-ITL/control hearts: n = 387). Genome-wide analyses were carried out on each of the determined phenotypes (gross cardiac lesions) using a medium density single nucleotide polymorphism (SNP) chip and 500 kb windows/regions for analysis, with 250 kb regions of overlap. The distribution derived by a multidimensional scaling (MDS) analysis of all phenotypes demonstrated a lack of complete separation between phenotypes of affected and unaffected animals, which made diagnosis difficult. Although genetic differences were small, a few genes associated with dilated cardiomyopathy (DCM) and arrhythmogenic right ventricular cardiomyopathy (ARVM) were identified. In addition, multiple genes associated with cardiac arrhythmias and ventricular hypertrophy were identified that can possibly result in heart failure. The results of this preliminary study did not provide convincing evidence that a single, heritable cardiomyopathy is the cause of heart failure in ITL pigs.     

Osteocartilaginous metaplasia in the right atrial myocardium of healthy adult sheep.

Among 172 hearts from clinically normal adult sheep aged 1.5 to 7 years evaluated for the presence of cartilage and/or bone in the right atrial myocardium, 3.49% (6/172) had palpable evidence of osteocartilaginous foci. An additional 8% prevalence was estimated based on radiographs of hearts that contained < or =1 mm foci of nonpalpable, radiographically dense bone. Microscopically, the nodules in the atria were characterized by mature lamellar bone enclosing adipose tissue, with occasional new bone formation by endochondral ossification. No degenerative changes were evident in the affected atrial myocardium, suggesting that these lesions were clinically insignificant background changes.     

Plastinated heart slices aid echocardiographic interpretation in the dog

Our aim was to compare plastinated sections of the canine heart with corresponding two-dimensional (2D) echocardiographic images. Thirteen dog hearts were fixed by dilation and then processed by the S10 silicon plastination method (Biodur). Two dogs without evidence of cardiac disease were imaged using 2D echocardiography so as to obtain a complete series of the standard right and left parasternal images, which were compared with corresponding plastinated slices obtained by knife sectioning of the hearts. The plastinated slices revealed the internal anatomy of the heart with great detail and were particularly useful to display the spatial relationship between complex anatomic structures. The plastinated slices corresponded accurately with the echocardiographic images. Because of the dilation of the right heart during the fixation process, it was not possible to obtain plastinated specimens in ventricular systole. This paper may be a reference atlas for assisting 2D echocardiography interpretation.     

绵羊心壁组织学结构特征的研究

分别制作绵羊左、右心房,左、右心室石蜡组织切片,通过HE、改良PTAH染色法研究绵羊心壁的组织结构特征。结果发现绵羊心壁由心内膜、心肌膜和心外膜构成,心内膜中富含浦肯野纤维;心肌膜最厚,心肌纤维较细,呈螺旋状环绕分层排列;心外膜内可见大量脂肪细胞。改良PTAH染色将肌纤维染成紫蓝色,闰盘着色深蓝,纤维结缔组织染成玫瑰红色。研究结果表明,绵羊心肌纤维较细,肌纤维横纹清晰,闰盘较稀疏。H2O2因其氧化和漂白作用,在改良PTAH染色中有一定的作用。     

The heart remembers: observations of cardiac memory in the Dorper sheep heart

Memory is a property common to a diverse range of tissues. Cardiac memory has been demonstrated in the human, dog, rat and rabbit. This is a peculiar phenomenon, reflected in the T wave of the electrocardiogram. The heart is able to remember periods of alterations in the sequence of ventricular activation and once there is a return to a normal sequence of ventricular activation the T waves may manifest memory. Cardiac memory is noted when the T wave during normal ventricular activation retains the vector of the previous abnormal QRS complex, caused by a period of altered ventricular activation. Possible mechanisms of memory in the heart are alterations of the transient outward potassium current (I10) in ventricular myocytes and new protein synthesis inside myocytes. These two mechanisms operate in short- and long-term cardiac memory respectively. Currently, it is unknown whether memory may have adverse structural consequences in the heart. We were able to demonstrate memory in the hearts of Dorper wethers and this is the first report of cardiac memory in Dorper sheep.     

A morphometric study of foetal and newborn cardiac growth in the horse

A morphometric study of hearts in 81 equine foetuses, ranging in age from 190 to 330 days of foetal age, and in 26 newborn foals is reported. The mean weight, external dimensions, ventricular wall thickness and circumference of the atrio-ventricular orifice were measured. Features of the main associated vessels of the heart were also recorded. All cardiac measurements of foetuses increased linearly throughout the latter half of pregnancy and were highly correlated with foetal age. This linear growth pattern was also found in the parameters of the associated arterial trunks. The ratio of the right ventricular weight to the total ventricular weight in the equine foetuses increased gradually from 0.27 (Day 190) to 0.34 (full term), but in newborn foals, this ratio began to decrease soon after birth, declining from 0.32 to 0.28 by 11 days of age. The interventricular septum was thickest followed by the right ventricular wall, and the left ventricular wall was thinnest during the period of gestation studied. The right ventricle was 3.2 per cent to 31.5 per cent thicker than the left ventricle.     

Pathophysiologic mechanism of cardiac dysfunction in experimentally induced heartworm caval syndrome in dogs: an echocardiographic study

In dogs with experimentally induced heartworm infection, the onset of caval syndrome (CS) was characterized by a murmur, loudest over the tricuspid valve, and a large worm mass in the right ventricular lumen detectable during diastole by use of M-mode echocardiography. Two-dimensional echocardiography indicated that the worm mass was located in the right atrium and venae cavae and was "flowing" into the right ventricle during rapid diastolic filling. Paradoxical septal motion and vigorous right ventricular cranial wall motion also were observed. Other echocardiographic changes included decreased size of the left atrium and ventricle, aortic root, and ratio of left-to-right ventricular diastolic luminal diameter, compared with values obtained 6 months after experimentally induced heartworm infection. Right ventricular end diastolic diameter increased considerably. Most echocardiographic indices of left ventricular function (fractional shortening, velocity of circumferential fiber shortening, ejection fraction, and preejection period) were not altered appreciably, but estimates of cardiac index and stroke volume were markedly decreased. Electrocardiography revealed ventricular and supraventricular premature complexes in 7 of the 8 dogs studied, evidence of right ventricular enlargement in 6 of the 8 dogs studied, and increased mean heart rate, compared with that measured 6 months after inoculation of infective larvae, before the onset of CS. Cardiac catheterization was performed in 3 days at the onset of CS. Severe pulmonary arterial and right ventricular hypertension and decreased cardiac index (compared with values obtained before inoculation) were observed. Evidence of right ventricular inflow obstruction was not detected. Mean aortic blood pressure decreased with the onset of CS, but right ventricular end diastolic pressure increased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Morphology and Classification of Right Ventricular Bands in the Domestic Dog (Canis familiaris)

Ventricular bands, also designated as ‘false tendons’, are described as single or multiple strands that cross the ventricles and have no connection to valvular cusps. Previous work indicates these strands are present in the ventricles of humans and some animal hearts and not always associated with cardiac pathologies. Despite these previous studies, the published literature is limited in documenting the morphology of these strands and incidence in animals. In this study, examination of 89 hearts showed six types of ventricular bands in the right ventricle of the domestic dog. These bands were classified according to their prevalence and points of attachment. Type I extended from the interventricular septum to the ventricular free wall, type II connected a musculus papillaris parvus to the ventricular free wall and type III connected trabeculae carneae on the interventricular septum. Type IV connected the trabeculae carneae on the ventricular free wall, type V interconnected papillary muscles and type VI connected the interventricular septum to a papillary muscle. While the study of these ventricular bands provided additional information on the cardiac anatomy of the domestic dog, it also showed their clinical importance. Several studies have proposed that their position in the ventricle may interfere with cardiac catheterization and pacemaker lead placement or be misinterpreted during echocardiography.     

Ultrastructural and molecular changes in the left and right ventricular myocardium associated with ascites syndrome in broiler chickens raised at low altitude

The present study examines ultrastructural and molecular changes in ventricular myocardium associated with ascites cases in fast-growing broilers raised at low altitude. Extensive ultrastructural lesions were seen in the left and right ventricular myocardium of broilers with fulminant heart failure and ascites. Significant changes included lesions in the myofibril contractile apparatus, altered mitochondria, marked reduction in the myofibril component, and changes in the extracellular matrix (ECM) architecture. No lesions were observed in hearts of slow growing broilers, but mild to moderate changes (predominantly in the left ventriculum) were apparent in the hearts from some clinically normal, fast-growing broilers. SDS-PAGE profiles of washed myofibrils showed several distinctly different bands in preparations from left ventricular myocardium of ascitic birds. Western blot analysis of these samples revealed several fragments of myosin heavy chain, M-protein, and titin. Based on gelatinolytic activity, matrix metalloproteinases (MMP) in the cytosolic fraction of ventricular myocardium homogenates were identified as MMP-2. The relative activity of this enzyme appears to be considerably higher in preparations from broilers, particularly in the preparations from the left ventriculum of fast-growing broilers, in comparison to leghorns or slow growing broilers. The nature and distribution of the changes in the heart indicate that chronic cardiomyopathic process in the left ventricular myocardium occurs during the development of ascites. It is postulated that progressive deterioration of the left heart pump function caused by initial lesions in the left ventricular myocardium is a significant factor in the development of pulmonary hypertension and the pathogenesis of ascites in broilers raised at low altitude.     

CORYNEBACTERIUM PSEUDOTUBERCULOSIS INFECTION OF SHEEP: ROLE OF SKIN LESIONS AND DIPPING FLUIDS

Caseous lymphadenitis (CLA) infection was established experimentally in a total of 30, 2-tooth merino wethers. In the first experiment a broth culture of the causative organism, Corynebacterum pseudotuberculosis was placed directly on to a freshly shorn area on the right shoulder of 21 sheep after pretreatment with a defatting agent, water or 4 different commercial sheep dips. Within 6–13 days focal skin lesions appeared on 7 sheep and these were followed by abscessation of the right prescapular lymph node. Lung lesions of CLA developed in 6 sheep; 5 of which had skin lesions. In the second experiment C. Pseudotuberculosis broth culture was applied over the right shoulder region of 14 sheep, 24 hours post shearing. The 7 animals had only 1 application of the culture and the remaining 7 had 4 applications on consecutive days. A total of 9 of the 14 sheep developed skin lesions and subsequent CLA in the right prescapular lymph nod but there was no significant difference between the 2 methods of application. As part of the second experiment a broth culture of C. pseudotuberculosis was added to a commercial arsenical sheep dip and 2 hours later sprayed on to the right side of sheep shorn 24 hours or 2 weeks previously. Within 6–13 days all 14 sheep treated in this way developed skin lesions from which C. pseudotuberculiosis was recovered in dense pure growth. Healing time of skin lesions in all affected sheep ranged from 17–72 days post inoculation. A serological test to detect the presence of C. pseudotuberculosis antitoxin was used at regular intervals on all experimental sheep. The earliest positive reaction in an affected sheep was recorded 4 weeks post inoculation. In 23 known affected sheep tested at 35 weeks post inoculation, 10 were positive to the Zaki test. No false positive reactors were recorded. The localisation of focal lung lesions in the interstitial tissue suggests that pulmonary abscessation caused by C. pseudotuberculosis develops via the haematogenous route.     

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.