Combination of the Modified Loop Technique and De Vega Annuloplasty in Dogs with Mitral Regurgitation.

Background: Detailed surgical techniques for treating canine mitral regurgitation have not been previously reported. Method: This case series included six consecutive client-owned dogs with mitral regurgitation. All dogs underwent a combined protocol, including the modified loop technique and De Vega annuloplasty (MODEL surgery), in 2021. Artificial loops covering 80% of the length of the strut chordae tendineae were used for chordal replacement. Mitral annuloplasty was subjectively performed, targeting the circumference of the septal leaflet. Results: The breeds were Chihuahua-mixed breed, Spitz, Pomeranian, Cavalier King Charles Spaniel, and Chihuahua, with average ages and weights of 11.4 ± 2.3 years and 5.49 ± 2.98 kg, respectively. The aortic cross-clamp, pumping, and surgery times were 64.0 ± 7.5 min, 168.5 ± 39.1 min, and 321.0 ± 53.1 min, respectively. After MODEL surgery, left atrial-to-aortic ratios significantly decreased from 2.20 ± 0.18 to 1.26 ± 0.22 (p < 0.01), and left ventricular end-diastolic internal diameter normalized to body weight significantly decreased from 2.03 ± 0.26 to 1.48 ± 0.20 (p < 0.01). In all cases, the clinical signs disappeared or improved significantly. Conclusions: MODEL surgery increased mitral valve coaptation, normalized heart sizes, and significantly improved clinical signs in dogs with mitral regurgitation.

Assessment of left ventricular regional function in affected and carrier dogs with Duchenne muscular dystrophy using speckle tracking echocardiography.

BACKGROUND: Two-dimensional speckle tracking echocardiography (STE) is a relatively new method to detect regional myocardial dysfunction. To assess left ventricular (LV) regional myocardial dysfunction using STE in Duchenne muscular dystrophy model dogs (CXMD(J)) without overt clinical signs of heart failure. METHODS: Six affected dogs, 8 carrier dogs with CXMD(J), and 8 control dogs were used. Conventional echocardiography, systolic and diastolic function by Doppler echocardiography, tissue Doppler imaging (TDI), and strain indices using STE, were assessed and compared among the 3 groups. RESULTS: Significant differences were seen in body weight, transmitral E wave and E' wave derived from TDI among the 3 groups. Although no significant difference was observed in any global strain indices, in segmental analysis, the peak radial strain rate during early diastole in posterior segment at chordae the tendineae level showed significant differences among the 3 groups. CONCLUSIONS: The myocardial strain rate by STE served to detect the impaired cardiac diastolic function in CXMD(J) without any obvious LV dilation or clinical signs. The radial strain rate may be a useful parameter to detect early myocardial impairment in CXMD(J).

Long-term survival of a cow with cervical ectopia cordis.

This study investigated the long-term survival of a calf with cervical ectopia cordis that grew normally, became pregnant, and calved normally. The cow showed normal cardiac function and absence of peripheral circulation abnormalities. This paper documents antemortem characteristics of the affected cow.

Comparison of left ventricular contraction profiles among small, medium, and large dogs by use of two-dimensional speckle-tracking echocardiography.

OBJECTIVE: To assess differences in left ventricular contractile indices among dogs of 3 body sizes via 2-D speckle-tracking echocardiography (STE) and to determine body weight-independent systolic variables. ANIMALS: 37 clinically normal adult dogs. PROCEDURES: Dogs were allocated into 3 groups on the basis of body weight: small (<7kg), medium (7 to 20kg), and large (>20kg). Right parasternal short-axis echocardiographic views were acquired to measure conventional M-mode variables (left ventricular internal diameter at end diastole, left ventricular internal diameter at end systole, and fractional shortening [FS]) and STE indices (peak systolic strain, peak systolic strain rate, synchrony time index [STI], peak systolic apical rotation, peak systolic basal rotation, peak apical twisting rate, and peak systolic torsion). Values were compared among the 3 groups. RESULTS: STE indices, except for peak systolic radial strain (SRad), peak systolic basal rotation, and STI, were significantly decreased in large dogs, compared with values for small and medium dogs. No significant difference was detected in stroke index, peak systolic SRad, and peak systolic basal rotation among the 3 groups. The STI in large dogs was significantly increased, compared with that of medium dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Results revealed that decreased systolic indices in large dogs should not be interpreted as signs of decreased systolic function. Increased STI in large dogs may contribute to decreased FS. Because peak systolic SRad was not affected by body weight, peak systolic SRad might be a better variable than FS for assessing systolic function.

Selective vacuolar degeneration in dystrophin-deficient canine Purkinje fibers despite preservation of dystrophin-associated proteins with overexpression of Dp71.

BACKGROUND: Respiratory support therapy significantly improves life span in patients with Duchenne muscular dystrophy; cardiac-related fatalities, including lethal arrhythmias, then become a crucial issue. It is therefore important to more thoroughly understand cardiac involvement, especially pathology of the conduction system, in the larger Duchenne muscular dystrophy animal models such as dystrophic dogs. METHODS AND RESULTS: When 10 dogs with canine X-linked muscular dystrophy in Japan (CXMD(J)) were examined at the age of 1 to 13 months, dystrophic changes of the ventricular myocardium were not evident; however, Purkinje fibers showed remarkable vacuolar degeneration as early as 4 months of age. The degeneration of CXMD(J) Purkinje fibers was coincident with overexpression of Dp71 at the sarcolemma and translocation of mu-calpain to the cell periphery near the sarcolemma or in the vacuoles. Immunoblotting of the microdissected fraction showed that mu-calpain-sensitive proteins such as desmin and cardiac troponin-I or -T were selectively degraded in the CXMD(J) Purkinje fibers. Utrophin was highly upregulated in the earlier stage of CXMD(J) Purkinje fibers, but the expression was dislocated when vacuolar degeneration was recognized at 4 months of age. Nevertheless, the expression of dystrophin-associated proteins alpha-, beta-, gamma-, and delta-sarcoglycans and beta-dystroglycan was well maintained at the sarcolemma of Purkinje fibers. CONCLUSIONS: Selective vacuolar degeneration of Purkinje fibers was found in the early stages of dystrophin deficiency. Dislocation of utrophin besides upregulation of Dp71 can be involved with this pathology. The degeneration of Purkinje fibers can be associated with the distinct deep Q waves in ECG and fatal arrhythmia seen in dystrophin deficiency.

Comparison of the effects of candesartan cilexetil and enalapril maleate on right ventricular myocardial remodeling in dogs with experimentally induced pulmonary stenosis.

OBJECTIVE: To compare the effects of candesartan cilexetil and enalapril maleate on right ventricular myocardial remodeling in dogs with experimentally induced pulmonary stenosis. ANIMALS: 24 Beagles. PROCEDURES: 18 dogs underwent pulmonary arterial banding (PAB) to induce right ventricular pressure overload, and 6 healthy dogs underwent sham operations (thoracotomy only [sham-operated group]). Dogs that underwent PAB were allocated to receive 1 of 3 treatments (6 dogs/group): candesartan (1 mg/kg, PO, q 24 h [PABC group]), enalapril (0.5 mg/kg, PO, q 24 h [PABE group]), or no treatment (PABNT group). Administration of treatments was commenced the day prior to surgery; control dogs received no cardiac medications. Sixty days after surgery, right ventricular wall thickness was assessed echocardiographically and plasma renin activity, angiotensin-converting enzyme activity, and angiotensin I and II concentrations were assessed; all dogs were euthanatized, and collagenous fiber area, cardiomyocyte diameter, and tissue angiotensin-converting enzyme and chymase-like activities in the right ventricle were evaluated. RESULTS: After 60 days of treatment, right ventricular wall thickness, cardiomyocyte diameter, and collagenous fiber area in the PABNT and PABE groups were significantly increased, compared with values in the PABC and sham-operated groups. Chymase-like activity was markedly greater in the PABE group than in other groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that treatment with candesartan but not enalapril effectively prevented myocardial remodeling in dogs with experimentally induced subacute right ventricular pressure overload.

Effect of isoflurane anesthesia on hemodynamics following the administration of an angiotensin-converting enzyme inhibitor in cats.

The objective of this study was to evaluate the hemodynamics of the anesthetic isoflurane in healthy cats given angiotensin-converting enzyme inhibitor (ACEI). The 7 healthy young cats and 3 old cats were received placebo or enalapril 0.5 mg/kg orally. The change in systolic arterial pressure from the baseline to 30 min postanesthesia in the ACEI group was significantly higher than in the placebo group (mean +/- SD: -39 +/- 13% vs. -17 +/- 12%, respectively). The present study indicated that general anesthesia may induce hypotension after the administration of an ACEI.

Modulation of the tissue reninangiotensin-aldosterone system in dogs with chronic mild regurgitation through the mitral valve.

OBJECTIVE: To investigate whether the tissue and plasma renin-angiotensin-aldosterone system (RAAS) is activated in dogs with mild regurgitation through the mitral valve and determine the contribution of chymase and angiotensin-converting enzyme (ACE) to the activation of the RAAS and potential production of angiotensin II during the chronic stage of mild mitral valve regurgitation. ANIMALS: 5 Beagles with experimentally induced mild mitral valve regurgitation and 6 clinically normal (control) Beagles. PROCEDURES: Tissue ACE and chymase-like activities and plasma RAAS were measured and the RAAS evaluated approximately 1,000 days after experimental induction of mitral valve regurgitation in the 5 dogs. RESULTS: Dogs with experimentally induced mitral valve regurgitation did not have clinical signs of the condition, although echocardiography revealed substantial eccentric hyper- trophy. On the basis of these findings, dogs with mitral valve regurgitation were classified as International Small Animal Cardiac Health Council class Ib. Plasma activity of renin and plasma concentrations of angiotensin I, angiotensin II, and aldosterone were not significantly different between dogs with mitral valve regurgitation and clinically normal dogs. Tissue ACE activity was significantly increased and chymase-like activity significantly decreased in dogs with mitral valve regurgitation, compared with values in clinically normal dogs. CONCLUSIONS AND CLINICAL RELEVANCE: The tissue RAAS was modulated without changes in the plasma RAAS in dogs with mild mitral valve regurgitation during the chronic stage of the condition. An ACE-dependent pathway may be a major route for production of angiotensin II during this stage of the condition.

Cardiac involvement in Beagle-based canine X-linked muscular dystrophy in Japan (CXMDJ): electrocardiographic, echocardiographic, and morphologic studies.

BACKGROUND: Cardiac mortality in Duchenne muscular dystrophy (DMD) has recently become important, because risk of respiratory failure has been reduced due to widespread use of the respirator. The cardiac involvement is characterized by distinctive electrocardiographic abnormalities or dilated cardiomyopathy, but the pathogenesis has remained obscure. In research on DMD, Golden retriever-based muscular dystrophy (GRMD) has attracted much attention as an animal model because it resembles DMD, but GRMD is very difficult to maintain because of their severe phenotypes. We therefore established a line of dogs with Beagle-based canine X-linked muscular dystrophy in Japan (CXMDJ) and examined the cardiac involvement. METHODS: The cardiac phenotypes of eight CXMDJ and four normal male dogs 2 to 21 months of age were evaluated using electrocardiography, echocardiography, and histopathological examinations. RESULTS: Increases in the heart rate and decreases in PQ interval compared to a normal littermate were detected in two littermate CXMDJ dogs at 15 months of age or older. Distinct deep Q-waves and increase in Q/R ratios in leads II, III, and aVF were detected by 6-7 months of age in all CXMDJ dogs. In the echocardiogram, one of eight of CXMDJ dogs showed a hyperechoic lesion in the left ventricular posterior wall at 5 months of age, but the rest had not by 6-7 months of age. The left ventricular function in the echocardiogram indicated no abnormality in all CXMDJ dogs by 6-7 months of age. Histopathology revealed myocardial fibrosis, especially in the left ventricular posterobasal wall, in three of eight CXMDJ dogs by 21 months of age. CONCLUSION: Cardiac involvement in CXMDJ dogs is milder and has slower progression than that described in GRMD dogs. The distinct deep Q-waves have been ascribed to myocardial fibrosis in the posterobasal region of the left ventricle, but our data showed that they precede the lesion on echocardiogram and histopathology. These findings imply that studies of CXMDJ may reveal not only another causative mechanism of the deep Q-waves but also more information on the pathogenesis in the dystrophin-deficient heart.

Feasibility of radial and circumferential strain analysis using 2D speckle tracking echocardiography in cats.

The purpose of the present study is to investigate the feasibility of strain analysis using speckle tracking echocardiography (STE) in cats and to evaluate STE variables in cats with hypertrophic cardiomyopathy (HCM). Sixteen clinically healthy cats and 17 cats with HCM were used. Radial and circumferential strain and strain rate variables in healthy cats were measured using STE to assess the feasibility. Comparisons of global strain and strain variables between healthy cats and cats with HCM were performed. Segmental assessments of left ventricle (LV) wall for strain and strain rate variables in cats with HCM were also performed. As a result, technically adequate images were obtained in 97.6% of the segments for STE analysis. Sedation using buprenorphine and acepromazine did not affect any global strain nor strain rate variable. In LV segments of cats with HCM, reduced segmental radial strain and strain rate variables had significantly related with segmental LV hypertrophy. It is concluded that STE analysis using short axis images of LV appeared to be clinically feasible in cats, having the possibility to be useful for detecting myocardial dysfunctions in cats with diseased heart.

Dynamic left ventricular outflow tract obstruction secondary to hypovolemia in a German Shepard dog with splenic hemangiosarcoma.

Dynamic left ventricular outflow tract obstruction (DLVOTO) is a common condition in cats and humans. In this case report, a dog is described with DLVOTO secondary to severe intra-abdominal hemorrhage caused by a hemangiosarcoma. The dog was a 9-year-old, 35.7-kg, spayed female German Shepard dog that presented with a history of tachypnea and collapse. A Levine II/VI systolic murmur was present at the heart base. Abdominal ultrasonography revealed a splenic mass and a large amount of ascites. Echocardiography showed a reduced left ventricular diameter and an increased aortic velocity caused by systolic anterior motion (SAM) of the mitral valve apparatus. The heart murmur and the SAM were resolved after treatment including a splenectomy and a blood transfusion.

Time course sequences of angiotensin converting enzyme and chymase-like activities during development of right ventricular hypertrophy induced by pulmonary artery constriction in dogs.

ACE and chymase play crucial roles in the establishment of pressure overload-induced cardiac hypertrophy. In the present study, time sequences of ACE and chymase-like activities, and their correlation with hypertrophic changes including free wall thickness and cardiac fibrosis, were elucidated in dogs with constant pressure overload to the right ventricle. Pulmonary artery banding (PAB) was applied so that the diameter of the main pulmonary artery was reduced to 60% of the original size, right ventricular pressure was elevated by about 70%, and pulmonary artery flow was increased by about three times of that in sham operation groups. These increases remained unchanged 15, 60, and 180 days after PAB, suggesting that constant right ventricular pressure overload was obtained, at least during this period. The diameter of the right ventricular myocyte was slightly increased and the percentage of fractional shortening was decreased 15 days after PAB. Right ventricular wall thickness and interstitial collagenous fiber were, however, not different from those of sham-operated dogs, suggesting that this period is a period of adaptation to the overload. Sixty days after PAB, the diameter of the right ventricular myocyte was further increased, and right ventricular wall thickness and interstitial collagenous fiber were also increased. These changes were almost identical even 180 days after PAB. Thus, stable hypertrophy was elicited from 60 through 180 days after PAB. ACE activity was facilitated at the adaptation period to the overload (15 days after PAB), but chymase activity was not facilitated at this period. On the other hand, both ACE and chymase-like activities were unchanged in the earlier phase (60 days after PAB) of stable hypertrophy, but facilitated in the latter phase (180 days after PAB). These findings suggest the pathophysiologic roles of these enzymes may be different over the time course of pressure overload-induced hypertrophy.

Transcatheter closure of congenital ventricular septal defects in 3 dogs with a detachable coil.

The purpose of this study was to evaluate the feasibility, safety, and efficacy of transcatheter closure in dogs with a congenital perimembranous ventricular septal defect (VSD) by using a detachable coil. No dogs showed any symptoms, and results of chest X-rays and ECGs were normal. The diameters of VSD ranged from 2 to 4 mm on echocardiogram. The defect was 2-2.5 mm from the aortic valve. A detachable coil (size 5 mm with 5 loops) designed for patent ductus arteriosus was delivered via the transarterial route. The device was successfully employed in all dogs. A minimal residual shunt was observed in all dogs even though Qp/Qs decreased. Hemolysis and a rate-dependent right-bundle branch block were observed in 1 dog, but there was no clinical significance. No major complication was noted. Pathologic examination after 1 year revealed that the coils were covered with tissue without significant damage to the His-Purkinje conduction system. In conclusion, transcatheter closure of a small perimembranous VSD with a detachable coil can be achieved without major complications or significant pathologic damage at the lesion site.

Primary cardiac fibrosarcoma in a dog.

A primary cardiac fibrosarcoma in the right atrium of a 6-year-old Chihuahua dog is described. At necropsy, there was a firm, whitish and spherical mass in the right atrium. Histopathologically, the mass had moderate cellularity composed of spindle-shaped cells with scattered multinucleated giant cells. The tumor cells were arranged in interwoven bundles and sheets in the collagenous stroma. No metastases were observed. Ultrastructurally, the tumor cells mainly consisted of fibroblasts. Multinucleated giant cells did not have any certain organelles that would indicate a higher order of differentiation. Primary cardiac sarcomas in dogs are extremely rare.

Spectral analysis of heart rate variability in dogs with mild mitral regurgitation.

OBJECTIVE: To assess autonomic function in dogs with mild mitral regurgitation (MR) that did not have clinical signs of the condition. ANIMALS: 6 healthy adult Beagles. PROCEDURE: Mild MR was experimentally induced. A 24-hour ambulatory ECG was recorded before and after induction of MR. Heart rate variability was analyzed in frequency domains by use of the ambulatory ECG. Low-frequency (LF) and high-frequency (HF) power were calculated by integrating over their frequency intervals, and the ratio of LF to HF was also calculated. Measurements of frequency domains were analyzed for 4 time periods (midnight to 6 AM, 6 AM to noon, noon to 6 PM, and 6 PM to midnight). RESULTS: Dogs with experimentally induced MR were classified as International Small Animal Cardiac Health Council class Ia. The HF power of dogs with MR was significantly decreased between 6 AM and noon. The ratio of LF to HF in dogs with MR was significantly increased for the periods between midnight and 6 AM, 6 AM and noon, and noon and 6 PM. CONCLUSIONS AND CLINICAL RELEVANCE: Compensatory response through autonomic modulation was observed in dogs with mild MR that did not have abnormalities, except for cardiac murmur, during clinical examination. This result suggests that treatment during the early stages of mild MR may be beneficial. Additional studies are necessary to determine whether such treatment will delay the onset of congestive heart failure and prolong survival in dogs affected with mild MR.

Scanning electron microscopy of vascular corrosion casts and histologic examination of pulmonary microvasculature in dogs with dirofilariosis.

OBJECTIVE: To characterize structural changes in pulmonary vessels of dogs with dirofilariosis. ANIMALS: 8 dogs with dirofilariosis and 2 unaffected control dogs. PROCEDURE: Pulmonary artery pressure was measured in affected dogs, and dogs then were euthanatized. Scanning electron microscopy was used to examine vascular corrosion casts of pulmonary vasculature. Tissue sections of pulmonary vasculature were evaluated by use of histologic examination. RESULTS: Pulmonary artery pressure was higher in dogs with severely affected pulmonary vessels. In tissue sections, dilatation, as well as lesions in the tunica intima and proliferative lesions resulting in constriction or obstruction, were frequently observed in branches of the pulmonary artery. Numerous dilated bronchial arteries were observed around affected pulmonary arteries. Hyperplastic venous sphincters were observed in small pulmonary veins and venules. In corrosion casts, affected pulmonary lobar arteries had dilatation, pruning, abnormal tapering, constriction, and obstruction. In small arteries and arterioles, surface structures representing aneurisms and edema were seen. Bronchial arteries were well developed and extremely dilated, and they formed numerous anastomoses with pulmonary arteries at all levels, from the pulmonary trunk to peripheral vessels. Capillaries in the lungs were dilated with little structural change. Small pulmonary veins and venules had irregular annular constrictions that were caused by hyperplastic smooth muscle cells of venous sphincters. CONCLUSIONS AND CLINICAL RELEVANCE: Scanning electron microscopy of microvascular casts delineated links between the bronchial and pulmonary circulations in dogs with dirofilariosis. Results of scanning electron microscopy provided a structural explanation for the development of pulmonary circulatory disturbances and pulmonary hypertension in dogs affected by dirofilariosis.

Modified loop technique in three dogs with mitral regurgitation.

Mitral valvuloplasty (MVP) is used in dogs with refractory mitral regurgitation (MR); however, it is difficult to tie the artificial chord, i.e., the expanded polytetrafluoroethylene suture, at the planned height of the mitral valve, because of the slippery nature of the knot. The loop technique has resolved these difficulties in humans. Premanufactured loops (length, 8.0-15.0 mm with 1.0-mm increments) were used in the new modified loop technique. In the current study, cardiac murmurs disappeared, and the MR markedly improved or completely disappeared approximately 3 months after surgery in 3 dogs. Therefore, this new technique might be effective in dogs.

Arteriovenous shunts resembling patent ductus arteriosus in dogs: 3 cases.

Three dogs presented for the evaluation of cardiac murmurs were diagnosed with aberrant arteriovenous shunts. All cases demonstrated the following findings: 1) relatively soft continuous murmur loudest at the left heart base resembling patent ductus arteriosus (PDA); 2) shunt flow signals in the pulmonary artery on echocardiography; and 3) no PDA on selective angiography, but evidence of anomalous shunting vessels from thoracic aorta to pulmonary vasculature. An aberrant arteriovenous shunt should be considered when a continuous murmur of relatively small intensity is heard.

Increased chymase-like activity in a dog with congenital pulmonic stenosis.

OBJECTIVES: This study was intended to compare the tissue chymase-like activity and angiotensin converting enzyme (ACE) activity in the right and left ventricles of a dog with congenital pulmonic stenosis (PS), with normal dogs, and to discuss the potential clinical implications of these findings. ANIMALS, MATERIALS AND METHODS: Study subjects included a one-year-old Beagle dog with spontaneous PS and six clinically normal Beagles. Chymase-like and ACE activities were determined in all hearts by high pressure liquid chromatography. RESULTS: In the PS dog right ventricular (RV) chymase-like activity (49.79 nmol/min/g tissue) and left ventricular (LV) chymase-like activity (36.85 nmol/min/g tissue) were elevated vs normal Beagle dogs (mean+/-standard deviation, RV: 20.17+/-5.24 nmol/min/g, LV: 19.03+/-3.27 nmol/min/g). CONCLUSIONS: Activation of the tissue RAA system was detected in a dog with congenital PS. This interesting finding should be pursued with further studies to validate this result, and to explore whether pharmacological blockade of chymase, or the angiotensin II receptor, represents a useful strategy to prevent myocardial remodeling in this condition.

Coil occlusion of residual shunts after surgical closure of patent ductus arteriosus.

UNLABELLED: OBJECTIVE; To describe use of coil embolization to occlude residual flow through a patent ductus arteriosus (PDA) after incomplete surgical ligation. STUDY DESIGN: Clinical study. ANIMALS: Dogs (n=4) with continuous murmur after surgical ligation of PDA. METHODS: After PDA ligation, residual ductal flow through the PDA was visible on color-flow Doppler examination and left ventricular end-diastolic diameter remained increased. Coil embolization by an arterial approach was performed to achieve complete occlusion of the PDA. RESULTS: Embolization coils were delivered without complications and hemodynamically successful occlusion was achieved. Doppler-visible flow resolved in 2 dogs within 3 months after embolization. Left ventricular end-diastolic diameter indexed to body weight decreased in all dogs. CONCLUSIONS: Transcatheter coil embolization appears to be a safe and minimally invasive procedure for complete occlusion of residual PDA flow after incomplete surgical ligation. CLINICAL RELEVANCE: Transcatheter coil embolization should be considered for correction of hemodynamically significant residual shunts in dogs that have incomplete PDA occlusion after open surgical ligation.