Beyond Angiotensin-Converting Enzyme Inhibitors: Modulation of the Renin-Angiotensin-Aldosterone System to Delay or Manage Congestive Heart Failure

The renin-angiotensin-aldosterone system (RAAS) consists of bioactive angiotensin peptides, enzymatic pathways, receptors, and the steroid hormone aldosterone. The RAAS regulates blood pressure, sodium, and electrolyte homeostasis and mediates pathologic disease processes. Within this system is an alternative arm that counterbalances the vasoconstrictive, sodium and water retentive, and pro-fibrotic and inflammatory effects of the classical arm. Improved biochemical methodologies in RAAS quantification are elucidating how this complex system changes in health and disease. Future treatments for cardiovascular and kidney disease will likely involve a more nuanced manipulation of this system rather than simple blockade.

Use of serum osmolality to identify heart disease stage in dogs and relationship to mathematical chloride correction

BACKGROUND

Heart failure-associated hypochloremia can be depletional from diuretics or dilutional from water retention. Serum osmolality reflects water balance but has not been evaluated in dogs with heart disease.

HYPOTHESIS

To determine if serum osmolality is related to heart disease stage and amount of mathematical correction of serum chloride (Cl- ) concentrations in healthy dogs and dogs with myxomatous mitral valve degeneration (MMVD).

ANIMALS

Seventy-seven dogs (20 healthy, 25 Stage B MMVD, 32 Stage C/D MMVD).

METHODS

Serum Cl- concentrations were mathematically corrected. Osmolality was calculated (calOsm) and directly measured by freezing point depression (dmOsm) and compared by Bland-Altman analysis. Biochemical variables and osmolality were compared among healthy, Stage B, and Stage C/D dogs. Correlations were explored between osmolality and biochemical variables. Median and range are presented. P < .05 was considered significant.

RESULTS

The calOsm was different among groups (P = .003), with Stage B (310 mOsm/kg; 306, 316) and C/D dogs (312 mOsm/kg; 308, 319) having higher calOsm than healthy dogs (305 mOsm/kg; 302, 308). Osmolality methods were moderately correlated (P < .0001, rs  = .46) but with proportional bias and poor agreement. The amount of Cl- correction was negatively correlated with calOsm (P < .0001, rs  = -.78) and dmOsm (P = .004, rs  = -.33). Serum bicarbonate concentration was negatively correlated with Cl- (P < .0001, rs  = -.67).

CONCLUSIONS AND CLINICAL IMPORTANCE

Dogs with Stage B and Stage C/D heart disease had higher calOsm than healthy dogs. Osmolality was inversely related to the amount of Cl- correction, which supports its use in assessing relative body water content. Poor agreement between calOsm and dmOsm prevents methodological interchange.

Angiotensin-converting enzyme 2 in dogs with Dirofilaria immitis

BACKGROUND

Infection by the canine heartworm, Dirofilaria immitis, causes significant cardiopulmonary disease, with progression impacted by increasing parasite numbers and duration of infection. The renin-angiotensin-aldosterone system (RAAS) is an important mediator of cardiac and pulmonary disease. Angiotensin-converting enzyme 2 (ACE2) mitigates the maladaptive effects of angiotensin II by converting it to angiotensin (1-7). We hypothesized that circulating ACE2 activity would be altered in dogs with high heartworm infection intensities relative to dogs without heartworms.

METHODS

Frozen serum samples (-80 °C) from 30 dogs euthanized at Florida shelters were analyzed for ACE2 activity using liquid chromatography-mass spectrometry/mass spectroscopy and a kinetics approach with and without an ACE2 inhibitor. A convenience sample of 15 dogs without heartworms (HW0) and 15 dogs with > 50 heartworms (HW>50) was included. Heartworm number and microfilariae presence were determined at necropsy. The effects of heartworm status, body weight, and sex on ACE2 were evaluated using regression analysis. Values of P < 0.05 were considered significant.

RESULTS

All HW0 dogs were D. immitis microfilariae-negative and all HW>50 dogs were D. immitis microfilariae-positive with a median adult worm count of 74 (minimum = 63, maximum = 137). The ACE2 activity of HW>50 dogs (median = 28.2 ng/ml; minimum = 13.6, maximum = 76.2) was not different from HW0 dogs (median 31.9 ng/ml; minimum = 14.1, maximum = 139.1; P = 0.53). The ACE2 activity was higher in dogs with high body weight (median 34.2 ng/ml minimum = 14.1, maximum = 76.2) than in dogs with low weight (median 27.5 ng/ml; minimum = 16.4, maximum = 139.1; P = .044).

CONCLUSIONS

Heartworm infection did not impact ACE2 activity in shelter dogs with or without heartworms, but heavier dogs had higher ACE2 activity compared to lighter dogs. Comprehensive RAAS evaluation and additional clinical information would aid in understanding how ACE2 activity relates to the entire cascade and clinical status in dogs with heartworm disease.

Metabolomic profiling in dogs with dilated cardiomyopathy eating non-traditional or traditional diets and in healthy controls

Dilated cardiomyopathy (DCM), caused by genetic and environmental factors, usually progresses to heart failure, a major cause of death in elderly people. A diet-associated form of DCM was recently identified in pet dogs eating non-traditional (NT) diets. To identify potential dietary causes, we analyzed metabolomic signatures and gene set/pathway enrichment in (1) all dogs based on disease, diet, and their interactions and (2) dogs with DCM based on diet. Metabolomic analysis was performed in 38 dogs with DCM eating NT diets (DCM-NT), 8 dogs with DCM eating traditional diets, 12 healthy controls eating NT diets, and 17 healthy controls eating traditional diets. Overall, 153 and 63 metabolites differed significantly between dogs with DCM versus healthy controls and dogs eating NT versus traditional diets, respectively, with 12 metabolites overlapping both analyses. Protein-protein interaction networks and gene set enrichment analysis identified 105 significant pathways and gene sets including aging-related pathways (e.g., nuclear factor-kappa B, oxidative damage, inflammation). Seventeen metabolites differed significantly in dogs with DCM eating NT versus traditional diets (e.g., fatty acids, amino acids, legume biomarkers), suggesting different mechanisms for primary versus diet-associated DCM. Our multifaceted metabolomic assessment of DCM in dogs highlighted diet's role in some forms of DCM.

Influence of sex on renin-angiotensin-aldosterone system metabolites and enzymes in Doberman Pinschers

BACKGROUND

Estrogen modulates the renin-angiotensin-aldosterone system (RAAS) in women, but sex differences have not been fully explored in dogs.

OBJECTIVE

We hypothesized that the RAAS profile of intact female (IF) Doberman Pinschers (DP) would differ from spayed female (SF) and intact male (IM) DP.

ANIMALS

Eighteen healthy DP (6 IF, 6 SF, 6 IM).

METHODS

Absolute and indexed RAAS metabolites, angiotensin-converting enzyme (ACE) and ACE2 activities, and genotypes (pyruvate kinase dehydrogenase 4, titin, and ACE variants) were compared among sex groups using Kruskal-Wallis or chi-square tests, and linear regression controlling for age. Data are expressed as median (minimum, maximum) and P < .05 was considered significant.

RESULTS

The ACE activity was higher in IF DP (656 pmol/L; 436, 784) compared to SF DP (411 pmol/L; 287, 451; P = .01) and IM DP (365 pmol/L; 276, 1200; P = .04) after controlling for age. Angiotensin II, angiotensin I, and plasma renin activity marker (PRA-S) were higher in IF DP compared to SF DP, but not significantly (P ≤ .25). After controlling for age, angiotensin 1-7/angiotensin I was lower in IF DP compared to SF DP (P = .01). Genotypes did not differ among groups. Most DP (94%) were ACE variant positive.

CONCLUSIONS AND CLINICAL SIGNIFICANCE

Sex and reproductive status influenced the RAAS of DP, with IF DP showing genotype-independent higher ACE activity. These findings hold implications for sterilization practices in female dogs, and support sex and reproductive status as a source of variability in RAAS studies. Additionally, the frequency of the ACE gene variant was very high in this group of DP.

Retrospective evaluation of risk factors for development of kidney injury after parenteral furosemide treatment of left-sided congestive heart failure in dogs

BACKGROUND

Kidney injury (KI) has been documented in dogs treated with furosemide for left-sided congestive heart failure (CHF).

HYPOTHESIS/OBJECTIVES

Determine risk factors for development of KI in furosemide-treated dogs and determine the effect of KI on survival.

ANIMALS

Seventy-nine client-owned dogs receiving parenteral furosemide for CHF.

METHODS

Serum creatinine (sCr) and electrolyte concentrations were determined during hospitalization and at first outpatient reevaluation to detect and stage KI (increase in sCr ≥0.3 mg/dL). Furosemide dosage administered between timepoints was calculated. Multivariable modeling was performed to identify predictors of KI and percent change in serum biochemistry results over time.

RESULTS

Kidney injury was identified in 38/79 (48%) dogs and mostly occurred during hospitalization. Kidney injury was Grade I in 25 dogs, Grade II in 9 dogs, and Grade III in 4 dogs. Higher blood pressure was associated with acute KI during hospitalization (odds ratio, 1.03; 95% confidence interval [95% CI] 1.01-1.07; P = .03) whereas PO furosemide dosage was associated with KI after hospital discharge (odds ratio, 7.77; 95% CI, 2.05-68.6; P = .02). Baseline sCr and use of a furosemide continuous rate infusion were not associated with increased risk of KI. Kidney injury was not associated with long-term outcome. Of 13 dogs with Grade II-III KI, azotemia was reversible in 9 dogs, and 6 dogs survived >1 year after KI.

CONCLUSIONS AND CLINICAL IMPORTANCE

In this cohort of dogs receiving parenteral furosemide for CHF, KI was common, mostly nonazotemic (Grade I), and did not impact survival.

Untargeted global metabolomic profiling of healthy dogs grouped on the basis of grain inclusivity of their diet and of dogs with subclinical cardiac abnormalities that underwent a diet change

OBJECTIVE

To compare metabolomic profiles of dogs eating grain-free (GF) versus grain-inclusive (GI) diets (1) for healthy dogs at baseline and (2) for dogs with subclinical cardiac abnormalities at 12 months after a diet change.

SAMPLE

Serum samples from 23 dogs eating GF diets and 79 dogs eating GI diets, of which 17 (8 eating a GF diet and 9 eating a GI diet) were reevaluated 12 months after a diet change.

PROCEDURES

Metabolomic profiles were developed by means of ultrahigh-performance liquid chromatography-tandem mass spectroscopy of serum samples. Baseline results for the GF group were compared with those for the GI group. Dogs from both groups with subclinical cardiac abnormalities were transitioned to a GI, pulse-free, intervention diet, and samples collected 12 months later were compared between diet groups. Statistical significance for biochemical group differences was defined as P < .05 with a false discovery rate (q) < .10.

RESULTS

Baseline differences in lipid metabolism and amino acid metabolism were found between the GF and GI diet groups. There were 46 metabolites that were higher and 82 metabolites that were lower in the GF group (n = 23), compared with the GI group (79). Comparison of the GF (n = 8) and GI (9) groups 12 months after the diet change showed only 6 metabolites that were higher and 11 metabolites that were lower in the GF group, compared with the GI group.

CLINICAL RELEVANCE

Metabolomic pathway differences between dogs eating GF versus GI diets highlight the important effect of diet in metabolomics analyses. The clinical importance of these differences and how they might relate to cardiac disease in dogs remains undetermined.

Association of diet with clinical outcomes in dogs with dilated cardiomyopathy and congestive heart failure

INTRODUCTION

Dilated cardiomyopathy (DCM) in dogs has been associated with feeding of grain-free (GF), legume-rich diets. Some dogs with presumed diet-associated DCM have shown improved myocardial function and clinical outcomes following a change in diet and standard medical therapy.

HYPOTHESIS

Prior GF (pGF) diet influences reverse cardiac remodeling and clinical outcomes in dogs with DCM and congestive heart failure (CHF).

ANIMALS AND METHODS

A retrospective study was performed with 67 dogs with DCM and CHF for which diet history was known. Dogs were grouped by diet into pGF and grain-inclusive (GI) groups. Dogs in the pGF group were included if diet change was a component of therapy. Survival was analyzed using Kaplan-Meier curves and the Cox proportional-hazards model.

RESULTS

The median survival time was 344 days for pGF dogs vs. 253 days for GI dogs (P = 0.074). Statistically significant differences in median survival were identified when the analysis was limited to dogs surviving longer than one week (P = 0.033). Prior GF dogs had a significantly worse outcome the longer a GF diet was fed prior to diagnosis (P = 0.004) or if they were diagnosed at a younger age (P = 0.017). Prior GF dogs showed significantly greater improvement in normalized left ventricular internal diastolic diameter (P = 0.038) and E-point septal separation (P = 0.031) measurements and significant decreases in their furosemide (P = 0.009) and pimobendan (P < 0.005) dosages over time compared to GI dogs.

CONCLUSIONS

Prior GF dogs that survived at least one week after diagnosis of DCM, treatment of CHF, and diet change had better clinical outcomes and showed reverse ventricular remodeling compared to GI dogs.

Myxomatous mitral valve disease in Miniature Schnauzers and Yorkshire Terriers: 134 cases (2007-2016)

OBJECTIVE

To characterize features of myxomatous mitral valve disease (MMVD) in Miniature Schnauzers and Yorkshire Terriers.

ANIMALS

69 Miniature Schnauzers and 65 Yorkshire Terriers, each with MMVD.

PROCEDURES

Medical record data for each dog were collected; the study period was January 2007 through December 2016. If available, radiographic data were evaluated, and a vertebral heart scale score was assigned for each dog. Statistical analysis was performed with Student t and Fisher exact tests.

RESULTS

Compared with Yorkshire Terriers, the prevalence of MMVD was significantly higher in Miniature Schnauzers and affected dogs were significantly younger at the time of diagnosis. Miniature Schnauzers were significantly more likely to have mitral valve prolapse and syncope, compared with Yorkshire Terriers. Yorkshire Terriers were significantly more likely to have coughing and have had previous or current treatment with cardiac medications, compared with Miniature Schnauzers. There was no statistical difference between breeds with regard to abnormally high vertebral heart scale scores or radiographic evidence of congestive heart failure.

CONCLUSIONS AND CLINICAL RELEVANCE

With regard to MMVD, features of the disease among Miniature Schnauzers and Yorkshire Terriers were similar, but there were also a few discernable differences between these 2 breeds and from historical findings for dogs with MMVD of other breeds. Clinical signs at the time of diagnosis differed between the 2 breeds, which may have reflected concurrent breed-specific conditions (sick sinus syndrome or airway disease [eg, tracheal collapse]). Future work should include prospective studies to provide additional information regarding the natural progression of MMVD in these dog breeds.

Prevalence of an angiotensin-converting enzyme gene variant in dogs

Background

Genetic heterogeneity of the canine angiotensin converting enzyme (ACE) gene is functionally important because the degree of aldosterone breakthrough with ACE-inhibitor therapy is greater in variant positive dogs compared to variant negative dogs, but the prevalence of the variant is not known. The purpose of this study was to determine ACE gene variant-positive prevalence in a population of 497 dogs of different breeds.

Results

Overall variant-positive prevalence was 31%, with 20% of dogs heterozygous and 11% of dogs homozygous. The variant was overrepresented in Irish Wolfhounds (prevalence 95%; P < .001), Dachshunds (prevalence 90%; P < .001), Cavalier King Charles Spaniels (prevalence 85%; P < .001), Great Danes (prevalence 84%; P < .001), and Bull Mastiffs (prevalence 58%; P = .02). Irish Wolfhounds were more likely to be homozygous than heterozygous (P < .001).

Conclusions

Nearly one-third of dogs in this study were positive for a functionally important ACE gene variant, with wide prevalence variability between breeds. The clinical importance of high ACE gene variant-positive prevalence in some breeds requires further study because the highest prevalences were found in breeds that are predisposed to heart disease and therefore may be treated with ACE-inhibitors.

Genetic differences in the angiotensin converting enzyme (ACE) have been shown to affect the way dogs respond to ACE-inhibitors, a class of medication which is used to treat dogs with heart disease. Dogs that have a genetic mutation of the ACE gene show less benefit with ACE-inhibitor medications than dogs without the mutation, but it is not known how common the mutation is in dogs. The purpose of this study was to determine the prevalence of this mutation (variant) in a large population of dogs of different breeds. The overall variant-positive prevalence in this population of 497 dogs was 31%. The variant was overrepresented in Irish Wolfhounds (prevalence 95%), Dachshunds (prevalence 90%), Cavalier King Charles Spaniels (prevalence 85%), Great Danes (prevalence 84%), and Bull Mastiffs (prevalence 58%). Irish Wolfhounds were more likely than other breeds to have 2 copies of the mutation (homozygous) than 1 copy of the mutation (heterozygous). The clinical importance of high ACE gene variant-positive prevalence in some breeds will require additional studies because some breeds are predisposed to heart disease, for which treatment with ACE-inhibitor medication might be recommended.

A deleterious mutation in the ALMS1 gene in a naturally occurring model of hypertrophic cardiomyopathy in the Sphynx cat

BACKGROUND

Familial hypertrophic cardiomyopathy is a common inherited cardiovascular disorder in people. Many causal mutations have been identified, but about 40% of cases do not have a known causative mutation. Mutations in the ALMS1 gene are associated with the development of Alstrom syndrome, a multisystem familial disease that can include cardiomyopathy (dilated, restrictive). Hypertrophic cardiomyopathy has not been described. The ALMS1 gene is a large gene that encodes for a ubiquitously expressed protein. The function of the protein is not well understood although it is believed to be associated with energy metabolism and homeostasis, cell differentiation and cell cycle control. The ALMS1 protein has also been shown to be involved in the regulation of cell cycle proliferation in perinatal cardiomyocytes. Although cardiomyocyte cell division and replication in mammals generally declines soon after birth, inhibition of ALMS1 expression in mice lead to increased cardiomyocyte proliferation, and deficiency of Alstrom protein has been suggested to impair post-natal cardiomyocyte cell cycle arrest. Here we describe the association of familial hypertrophic cardiomyopathy in Sphynx cats with a novel ALMS1 mutation.

RESULTS

A G/C variant was identified in exon 12 (human exon 13) of the ALMS1 gene in affected cats and was positively associated with the presence of hypertrophic cardiomyopathy in the feline population (p < 0.0001). The variant was predicted to change a highly conserved nonpolar Glycine to a positively charged Arginine. This was predicted to be a deleterious change by three in silico programs. Protein prediction programs indicated that the variant changed the protein structure in this region from a coil to a helix. Light microscopy findings included myofiber disarray with interstitial fibrosis with significantly more nuclear proliferative activity in the affected cats than controls (p < 0.0001).

CONCLUSION

This study demonstrates a novel form of cardiomyopathy associated with ALMS1 in the cat. Familial hypertrophic cardiomyopathy is a disease of genetic heterogeneity; many of the known causative genes encoding for sarcomeric proteins. Our findings suggest that variants in genes involved with cardiac development and cell regulation, like the ALMS1 gene, may deserve further consideration for association with familial hypertrophic cardiomyopathy.

A deleterious mutation in the ALMS1 gene in a naturally occurring model of hypertrophic cardiomyopathy in the Sphynx cat

Background

Familial hypertrophic cardiomyopathy is a common inherited cardiovascular disorder in people. Many causal mutations have been identified, but about 40% of cases do not have a known causative mutation. Mutations in the ALMS1 gene are associated with the development of Alstrom syndrome, a multisystem familial disease that can include cardiomyopathy (dilated, restrictive). Hypertrophic cardiomyopathy has not been described. The ALMS1 gene is a large gene that encodes for a ubiquitously expressed protein. The function of the protein is not well understood although it is believed to be associated with energy metabolism and homeostasis, cell differentiation and cell cycle control. The ALMS1 protein has also been shown to be involved in the regulation of cell cycle proliferation in perinatal cardiomyocytes. Although cardiomyocyte cell division and replication in mammals generally declines soon after birth, inhibition of ALMS1 expression in mice lead to increased cardiomyocyte proliferation, and deficiency of Alstrom protein has been suggested to impair post-natal cardiomyocyte cell cycle arrest. Here we describe the association of familial hypertrophic cardiomyopathy in Sphynx cats with a novel ALMS1 mutation.

Results

A G/C variant was identified in exon 12 (human exon 13) of the ALMS1 gene in affected cats and was positively associated with the presence of hypertrophic cardiomyopathy in the feline population (p < 0.0001). The variant was predicted to change a highly conserved nonpolar Glycine to a positively charged Arginine. This was predicted to be a deleterious change by three in silico programs. Protein prediction programs indicated that the variant changed the protein structure in this region from a coil to a helix. Light microscopy findings included myofiber disarray with interstitial fibrosis with significantly more nuclear proliferative activity in the affected cats than controls (p < 0.0001).

Conclusion

This study demonstrates a novel form of cardiomyopathy associated with ALMS1 in the cat. Familial hypertrophic cardiomyopathy is a disease of genetic heterogeneity; many of the known causative genes encoding for sarcomeric proteins. Our findings suggest that variants in genes involved with cardiac development and cell regulation, like the ALMS1 gene, may deserve further consideration for association with familial hypertrophic cardiomyopathy.

Visual representations of canine cardiac arrhythmias with Lorenz (Poincaré) plots

OBJECTIVE

To characterize the patterns associated with Lorenz plots (LPs) or Poincaré plots derived from the Holter recordings of dogs with various cardiac rhythms.

ANIMALS

77 dogs with 24-hour Holter recordings.

PROCEDURES

A 1-hour period from the Holter recordings from each of 20 dogs without arrhythmias and from each of 57 dogs with arrhythmias (10 each with supraventricular premature complexes, complex supraventricular ectopy, ventricular premature complexes, complex ventricular ectopy, and atrial fibrillation, and 7 with high-grade second-degree atrioventricular block) were used to generate the LPs. Patterns depicted in the LPs were described.

RESULTS

Arrhythmia-free Holter recordings yielded LPs with a Y-shaped pattern and variable silent zones. Recordings with single premature complexes yielded LPs with double side and triple side lobes. Complex ectopy was denoted by dots clustered in the lower left corner of the LPs. The LPs of recordings with atrial fibrillation had fan patterns consistent with a nonlinear relationship between atrial electrical impulses and atrioventricular nodal conduction. The recordings with atrioventricular block yielded LPs with island patterns consistent with variable atrioventricular nodal conduction.

CONCLUSIONS AND CLINICAL RELEVANCE

Distinct LP patterns were identified for common cardiac rhythms of dogs, supportive of nonrandom mechanisms as the cause of most rhythms. Visual interpretation of an LP generated from a Holter recording may aid in determining the arrhythmia type and understanding the arrhythmia's mechanism in dogs and other species.

Cross-Sectional Assessment of the Emotional Intelligence of Fourth-Year Veterinary Students and Veterinary House Officers in a Teaching Hospital

Emotional intelligence (EI) is the recognition and management of emotions. This skill set is important to work relationships and professional success. In this cross-sectional, observational study, we investigated EI scores of 4th-year veterinary students, interns, and residents in a teaching hospital, using a psychometric tool with professional population norms. Participants' EI scores were compared with professional norms and between the sample groups. Scores were examined on the basis of demographics and residency program type. Twenty-four 4th-year students and 43 interns and residents completed the survey. Total, composite, and subscale scores for all groups were lower than professional means. We noted no statistically significant differences in EI scores between training levels, but evaluation of effect sizes showed a medium negative effect of higher training levels on Self-Perception Composite, Self-Regard, Emotional Expression, Interpersonal Composite, Flexibility, and Optimism and a medium positive effect of higher training levels on Impulse Control. Medium effects for residency type were found for Stress Tolerance, Flexibility, and Stress Management, with higher scores for residencies with heavy inpatient loads. Medium effects for residency type were found on Flexibility scores, with higher scores for residents in disciplines with a perceived high stress level. We found that baseline EI scores of 4th-year veterinary students, interns, and residents at a teaching hospital were similar to, but uniformly lower than, those of other professionals and did not increase with training level. These results may be used to build on strengths and address weaknesses associated with EI of students and house officers at this institution.

Cardiac Leiomyosarcoma in a Cat Presenting for Bilateral Renal Neoplasia

A 10-year-old neutered female domestic longhair cat was presented to a tertiary care veterinary hospital for evaluation of a right renal mass that was identified incidentally on abdominal radiographs and classified further as a sarcoma based on fine needle aspiration cytology. Further diagnostic workup, including ultrasound and cytology, identified a sarcoma in the left kidney. After approximately 1 month of conservative medical management, the clinical condition deteriorated and the cat was humanely destroyed. Post-mortem examination confirmed bilateral renal masses with multifocal infarction and extensive necrosis, and further identified a large mass at the apex of the heart as well as multiple pulmonary nodules. Microscopical examination of the masses identified a population of poorly-differentiated neoplastic spindle cells, consistent with sarcoma. Immunohistochemically, the neoplastic cells expressed smooth muscle actin and muscle-specific actin, but were negative for myoglobin and factor VIII. Phosphotungstic acid-haematoxylin staining was unable to identify cross-striations in the neoplastic cells. Based on these results and the pattern of lesion distribution, the cat was diagnosed with cardiac leiomyosarcoma with pulmonary and bilateral renal metastasis.

Effect of atenolol on heart rate, arrhythmias, blood pressure, and dynamic left ventricular outflow tract obstruction in cats with subclinical hypertrophic cardiomyopathy

OBJECTIVE

To investigate the negative chronotropic, antiarrhythmic, and obstruction-relieving effects of atenolol in cats with subclinical hypertrophic cardiomyopathy (HCM).

ANIMALS

Seventeen cats with HCM.

METHODS

Results for echocardiography, electrocardiography, Doppler blood pressure, and 24 h Holter monitoring were compared in cats before and 2-4 weeks after atenolol therapy (6.25-12.5 mg PO q 12 h).

RESULTS

The left ventricular outflow tract maximum velocity (LVOT Vmax) decreased after atenolol administration (mean Vmax pre-treatment 3.3 m/s ± 1.8 m/s; post-treatment 1.6 m/s ± 1.0 m/s, p < 0.0001). Heart rate (HR) decreased after atenolol for all HR modalities. The total number of ventricular origin complexes (TotVent) and ventricular premature complexes (VPCs) decreased after atenolol. The VPCs decreased from a geometric mean of 61 complexes/24 h (range, 11-620 complexes/24 h) to 15 complexes/24 h (range, 1-1625 complexes/24 h) (p < 0.0001). Murmur grade decreased after atenolol from a median grade of 3/6 to 2/6 (p < 0.0001). The systolic blood pressure did not change (mean pre-treatment 130 mmHg ± 16 mmHg, mean post-treatment 123 mmHg ± 20 mmHg, p = 0.2).

CONCLUSION

Atenolol decreases HR, murmur grade, and LVOT obstruction, and to a lesser degree, frequency of ventricular ectopy, in cats with subclinical HCM. Further studies are needed to determine if sudden cardiac death or long-term outcome is influenced by atenolol administration.

Heart rate and arrhythmia frequency of normal cats compared to cats with asymptomatic hypertrophic cardiomyopathy

OBJECTIVES

To compare heart rate and arrhythmia frequency and complexity in a normal population of cats to a population of cats with hypertrophic cardiomyopathy (HCM).

ANIMALS

17 cats with HCM and 15 cats with normal echocardiograms.

METHODS

Results for echocardiography, electrocardiography, Doppler blood pressure, and 24-h Holter monitoring were compared between groups.

RESULTS

There was no difference in heart rate between HCM cats and normal cats regardless of modality used. All (17/17) HCM cats had ventricular arrhythmias (geometric mean 124 complexes/24 h) with 82% (14/17) exhibiting complex arrhythmias (couplets, triplets, or ventricular tachycardia). Most (14/15) normal cats had ventricular arrhythmias (geometric mean 4 complexes/24 h), but only 20% (3/15) exhibited complexity. HCM cats had significantly more total ventricular complexes, ventricular premature complexes and accelerated idioventricular rhythm than normal cats (P < 0.0001, P < 0.0001, and P = 0.01, respectively). Eighty eight percent (15/17) of HCM cats had supraventricular arrhythmias (geometric mean 9 complexes/24 h) with 23% (4/17) exhibiting complexity. Sixty percent (9/15) of normal cats had supraventricular arrhythmias (geometric mean 1 complex/24 h) with 13% (2/15) exhibiting complexity. Cats with hypertrophic cardiomyopathy had significantly more supraventricular complexes than normal cats (P = 0.0148).

CONCLUSION

Cats with asymptomatic HCM have more frequent and complex ventricular and supraventricular arrhythmias than normal cats but do not have different overall heart rates compared to normal cats. Further studies are needed to determine if these arrhythmias are associated with an increased risk of sudden cardiac death or influence long-term survival.

Cardiac troponin I concentrations in normal dogs and cats using a bedside analyzer

OBJECTIVE

To develop reference ranges for cardiac troponin I (cTnI) in normal dogs and cats using the Biosite Triage Meter((R)).

BACKGROUND

Reference ranges for cTnI in dogs and cats have not yet been reported for this inexpensive bedside analyzer.

METHODS

Purified free canine cTnI was diluted to 5 known concentrations to assess linearity and recovery. Interassay and intraassay precision were evaluated using 3 dilutions obtained from a dog with an elevated cTnI concentration. EDTA plasma was obtained from 55 normal dogs and 58 normal cats for analysis of cTnI.

RESULTS

Measured values of purified cTnI closely matched calculated concentrations (r(2)=0.997) and recovery ranged from 107-164%. Intraassay precision was 2.76+/-1.20% and interassay precision was 8.50+/-4.19%. The dogs were 4.8+/-3.1 years and 24.4+/-11.2kg (27 Mc, 19 Fs, 5 M, 4 F). The cats were 4.9+/-2.8 years and 5.1+/-1.19kg (36 Mc, 22 Fs). The median and range (5th and 95th percentile) of cTnI for dogs were <0.05ng/mL (<0.05-0.12). The median cTnI for cats was <0.05ng/mL, as was the range, because only 3 cats (the upper 5% of the population) had detectable cTnI concentrations. The lower limit of detection for this assay is 0.05ng/mL.

CONCLUSIONS

This study provides reference ranges for cTnI in dogs and cats using the Triage Meter((R)), an affordable bedside analyzer. The availability of reference ranges for this machine may increase clinical use and research of this marker in veterinary medicine.

Papillary muscle measurements in cats with normal echocardiograms and cats with concentric left ventricular hypertrophy

BACKGROUND

Papillary muscle hypertrophy can occur in conjunction with, or as the only indication of, hypertrophic cardiomyopathy or other diseases that result in left ventricular concentric hypertrophy (LVCH). Assessment of papillary muscle size is usually subjective because objective measures have not been reported.

HYPOTHESIS

The study hypothesis was that papillary muscle dimensions are different between normal cats and cats with LVCH.

ANIMALS

Echocardiograms from 44 normal cats and 40 cats with LVCH were included in the study.

METHODS

All measurements were taken from the right parasternal short-axis view at the level of the papillary muscles at end-diastole. Three methods were used to assess papillary muscle size: the area subtraction method, the direct area trace method, and the diameter method. Measurements were compared between cat groups and method comparisons were made among methods for area determination.

RESULTS

Cats with LVCH were older and had significantly greater left ventricular septal and free wall thicknesses and larger left atrial measurements than normal cats (P < .0006). Papillary muscle measurements were significantly greater by all measurement methods in cats with LVCH than in cats with normal echocardiograms (P < .0001). The area subtraction method and direct area trace method showed moderate agreement.

CONCLUSIONS AND CLINICAL IMPORTANCE

Papillary muscle measurements were larger for LVCH cats than normal cats; however, some overlap was present. The establishment of these objective measures adds to the echocardiographic examination of cats.

Cardiac evaluation of anesthetized Grevy's zebras(Equus grevyi)

OBJECTIVE

To determine ECG and echocardiographic measurements in healthy anesthetized Grevy's zebras (Equus grevyi).

ANIMALS

20 healthy zebras.

PROCEDURES

Auscultation, base-apex ECG, and echocardiography were performed on anesthetized zebras.

RESULTS

Low-grade systolic murmurs were detected in the left basilar region in 4 of 20 zebras. Evaluation of ECGs from 19 zebras revealed sinus rhythm with a predominantly negative QRS complex and a mean +/- SD heart rate of 67 +/- 10 beats/min. Echocardiograms of sufficient image quality were obtained for 16 zebras. Interventricular septal thickness in diastole, left ventricular chamber in diastole and systole, left atrial diameter, and left ventricular mass were significantly and moderately correlated with estimated body weight (r values ranged from 0.650 to 0.884). Detectable swirling of blood in the right and sometimes the left ventricles was detected in 9 of 16 zebras, whereas physiologic regurgitation of blood was detected for the aortic valve in 3 zebras, pulmonary valve in 2 zebras, mitral valve in 2 zebras, and tricuspid valve in 1 zebra.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this study provide reference information for use in the cardiac evaluation of anesthetized Grevy's zebras.

Comparison of canine cardiac troponin I concentrations as determined by 3 analyzers

BACKGROUND

Recent interest in cardiac biomarkers has led to the validation of several commercial analyzers for cardiac troponin I (cTnI) evaluation in dogs; however, these analyzers have not been standardized.

HYPOTHESIS

It was hypothesized that canine plasma cTnI concentrations as determined by 3 different analyzers would be similar.

ANIMALS

Twenty-three dogs with cardiac disease were studied.

METHODS

Reconstituted purified canine free cTnI was diluted with canine plasma to 8 concentrations (0.01, 0.1, 0.78, 1.56, 3.13, 6.25, 12.5, and 25 ng/mL), for analysis by 3 analyzers, the Biosite Triage Meter, the Dade-Behring Stratus, and the Beckman-Coulter Access AccuTnI. Plasma samples from 23 dogs with cardiac disease were also analyzed for cTnI concentrations on all analyzers.

RESULTS

Troponin I concentrations in sick dogs were <0.05-5.72 ng/mL (Biosite), 0.02-11.1 ng/mL (Access), and 0.02-9.73 ng/mL (Stratus). Analyzer results were highly correlated with each other (r = 0.97 to 1.0 for purified dilutions, r = 0.61 to 0.89 for samples from dogs); however, the limits of agreement were wide for both purified dilutions and clinical samples. Recovery was highest for the Access (334-1467%) and lowest for the Biosite (38-60%); Stratus 52-233%. Analyzer variability was lowest for the Access (1.2-10.4%) and highest for the Stratus (4.8-33.6%); Biosite 2.8-16.5%.

CONCLUSIONS AND CLINICAL IMPORTANCE

Results from this study suggest that although canine cTnI values obtained from the Biosite, Stratus, and Access analyzers are closely correlated, they cannot be directly compared with each other. In the absence of a gold standard none of the analyzers can be considered more correct than the others.

Echocardiographic estimation of systemic systolic blood pressure in dogs with mild mitral regurgitation

BACKGROUND

Systemic hypertension is likely underdiagnosed in veterinary medicine because systemic blood pressure is rarely measured. Systemic blood pressure can theoretically be estimated by echocardiography. According to the modified Bernoulli equation (PG = 4v(2)), mitral regurgitation (MR) velocity should approximate systolic left ventricular pressure (sLVP), and therefore systolic systemic blood pressure (sSBP) in the presence of a normal left atrial pressure (LAP) and the absence of aortic stenosis. The aim of this study was to evaluate the use of echocardiography to estimate sSBP by means of the Bernoulli equation.

HYPOTHESIS

Systemic blood pressure can be estimated by echocardiography.

ANIMAL

Seventeen dogs with mild MR. No dogs had aortic or subaortic stenosis, and all had MR with a clear continuous-wave Doppler signal and a left atrial to aorta ratio of < or = 1.6.

METHODS

Five simultaneous, blinded continuous-wave measurements of maximum MR velocity (Vmax) and indirect sSBP measurements (by Park's Doppler) were obtained for each dog. Pressure gradient was calculated from Vmax by means of the Bernoulli equation, averaged, and added to an assumed LAP of 8 mm Hg to calculate sLVP.

RESULTS

Calculated sLVP was significantly correlated with indirectly measured sSBP within a range of 121 to 218 mm Hg (P = .0002, r = .78). Mean +/- SD bias was 0.1 +/- 15.3 mm Hg with limits of agreement of -29.9 to 30.1 mm Hg.

CONCLUSION

Despite the significant correlation, the wide limits of agreement between the methods hinder the clinical utility of echocardiographic estimation of blood pressure.

Cardiac output measurement by partial carbon dioxide rebreathing, 2-dimensional echocardiography, and lithium-dilution method in anesthetized neonatal foals

The objective of this study was to assess 2 noninvasive methods of measuring cardiac output (CO) in neonatal foals by comparing results to that of the lithium-dilution method. Ten neonatal foals were anesthetized and CO was manipulated by varying the depth of anesthesia and infusion of dobutamine. Concurrent CO measurements were obtained by lithium dilution (reference method), partial carbon dioxide (CO2) rebreathing, volumetric echocardiography (cubic, Teichholz, Bullet, area-length, and single and biplane modified Simpson formulas), and transthoracic Doppler echocardiography. Thirty pairs of lithium-dilution/noninvasive CO measurements were taken from the 10 foals. For each method, relative bias was calculated as a percentage of the average CO. Lithium determinations of CO ranged between 3.09 and 1 1.1 L/min (mean +/- SD = 6.39 +/- 2.1 L/min), resulting in cardiac indices ranging between 79.0 and 209 mL/kg/min (mean +/- SD = 131 +/- 35.9 mL/kg/min). Relative bias of Doppler echocardiography significantly increased (P < .05), whereas that of partial CO2 rebreathing significantly decreased (P = .03) with increasing CO. Other methods were not influenced by the level of CO. Among methods not influenced by the level of CO, relative bias of the Bullet method (-4.2 +/- 20.9%; limits of agreement -45.2 to 36.7%) was significantly lower (P < .05) than that of each of the other noninvasive methods evaluated. Volumetric echocardiography using the Bullet method provides an accurate and noninvasive estimate of CO in anesthetized neonatal foals and warrants investigation in critically ill conscious foals.

Intermittent Bolus Injection versus Continuous Infusion of Furosemide in Normal Adult Greyhound Dogs

Several studies in human subjects have demonstrated greater diuresis with constant rate infusion (CRI) furosemide than intermittent bolus (IB) furosemide. This study was conducted to compare the diuretic efficacy of the same total dose of IB furosemide and CRI furosemide in 6 healthy, adult Greyhound dogs in a randomized crossover design with a 2-week washout period between treatments. For IB administration, dogs received 3 mg/kg at 0 and 4 hours. For CRI administration, dogs received a 0.66 mg/kg loading dose followed by 0.66 mg/kg/h over 8 hours. The same volume of fluid was administered for both methods. Urine output was quantified hourly. Urine electrolyte concentrations, urine specific gravity (USG), packed cell volume (PCV), total protein (TP), serum electrolyte concentrations, total carbon dioxide (TCO2), serum creatinine (sCr), and blood urea nitrogen (BUN) were determined every 2 hours. Urine production and water intake were greater (P < or = 0.05) for CRI than IB. Urine sodium and calcium losses were greater (P < 0.05) and urine potassium loss was less (P = 0.03) for CRI than IB, but there was no evidence of a difference between methods for urine magnesium and chloride losses. Serum chloride concentration was less (P < 0.001), sCr concentration greater (P = 0.04). TP greater (P = 0.01), and PCV greater (P = 0.003) for CRI than IB. No differences in USG, TCO2, BUN, or serum potassium, sodium, and magnesium concentrations were detected between methods. The same total dose of CRI furosemide resulted in more diuresis, natriuresis, and calciuresis and less kaliuresis than IB furosemide in these normal Greyhound dogs over 8 hours, suggesting that furosemide is a more effective diuretic when administered by CRI than by IB.

Short-Term Compatibility Of Furosemide With Crystalloid Solutions

Parenteral veterinary furosemide is a 50-mg/mL solution with a pH of 8.0-9.3. The purpose of this study was to determine whether a commonly used veterinary formulation of 50 mg/mL of furosemide solution could be diluted in vitro without precipitation. Furosemide 50 mg/mL was diluted to concentrations of 10 and 5 mg/mL with 5% dextrose in water (D5W), 0.9% saline, lactated Ringer solution (LRS), and sterile water. Acidic sterile water and basic sterile water solutions were made by the addition of hydrochloric acid and sodium hydroxide, respectively, for use as controls to assess the effect of pH extremes for each concentration. After furosemide dilution, the final pH of each sample was measured, and samples were grossly and microscopically examined for clarity and crystal formation immediately and 1, 3, 5, and 8 hours after dilution. Gross precipitation and microscopic crystals were immediately observed in the acidic controls. Solutions of 5 mg/mL in LRS and 0.9% saline became slightly cloudy immediately, but no crystals were observed microscopically for 8 hours. Solutions of 10 mg/mL in D5W, 0.9% saline, LRS, and sterile water and solutions of 5 mg/mL in D5W and sterile water and the basic control were grossly clear, and no microscopic crystals were observed for 8 hours. On the basis of the results obtained in this in vitro investigation, this veterinary formulation of furosemide 50 mg/mL can be diluted without precipitation to a concentration of 10 mg/mL with D5W, 0.9% saline, LRS, or sterile water and to 5 mg/mL with D5W or sterile water and held for 8 hours.

Evaluation of three peripheral arteriovenous fistulas for hemodialysis access in dogs

OBJECTIVE

To design and create 3 types of arteriovenous fistulas (AVF) in normal dogs, to monitor the dogs for secondary cardiovascular complications, and to verify adequacy of these fistulas for hemodialysis vascular access.

STUDY DESIGN

Experimental study.

ANIMALS

Four normal adult dogs.

METHODS

Cadaveric dissections were performed, and surgical protocols were generated for carotid-jugular (CJ), brachial-cephalic (BC), and distal caudal femoral-lateral saphenous anastomosis (DCFLS) AVF. Each surgical procedure was then performed in 2 live dogs. Echocardiography was performed at days 0, 1, 3, 7, 14, 28, and 56 to evaluate the dogs for evidence of volume overload secondary to AVF formation. Estimation of luminal diameter and confirmation of fistula patency were performed using percutaneous color Doppler ultrasound. At day 56, hemodialysis was performed using each fistula as a vascular access.

RESULTS

No significant changes occurred in the echocardiographic variables over time. All fistulas were patent at day 56 with mean luminal diameters of 4.5 mm (CJ), 4 mm (BC), and 1.5 mm (DCFLS). The BC fistula was superior for ease of needle placement and stabilization and provided adequate blood flow for clinical hemodialysis.

CONCLUSIONS

Based on this short-term study, arteriovenous fistulas appear to be a safe and effective means for hemodialysis access in dogs.

CLINICAL RELEVANCE

The arteriovenous fistulas described provide an alternative to the central venous catheters currently used for chronic hemodialysis access in dogs.

Efficacy of a single oral dose of isorsorbide 5-mononitrate in normal dogs and in dogs with congestive heart failure

Isosorbide 5-mononitrate (5-ISMN) was evaluated in normal dogs and dogs with congestive heart failure (CHF) in a randomized, blinded, and placebo-controlled study. Equilibrium blood pool imaging was used to detect changes in regional blood volume distribution. Six normal dogs were administered placebo, 2, 3, and 4 mg/kg 5-ISMN PO on separate days with a 1-week washout period between randomized dosings. Six dogs with CHF were administered placebo or 4 mg/kg 5-ISMN on separate days with a 1-week washout period between randomized dosings. Data were collected at baseline and at 15, 30, 45, 60, 90, 120, 150, 180, 210, and 240 minutes after dosing. Measured variables included indirect arterial blood pressure (BP), heart rate (HR), packed cell volume (PCV), scintigraphic count rates for normal dogs, and scintigraphic count rates for CHF dogs. Blood for plasma 5-ISMN concentration determination was collected at 60 minutes. Scintigraphic counts were corrected for decay and expressed as a percentage of the whole. No differences were detected in BP, HR, PCV, thoracic blood volume percentage (TBVP), or abdominal blood volume percentage (ABVP) between placebo and 5-ISMN in normal dogs at any dose. No differences were detected in TBVP or ABVP between placebo and 5-ISMN in dogs with CHF Plasma 5-ISMN concentration exceeded the minimum therapeutic concentration in all dogs and at all doses 60 minutes after drug administration. Equilibrium blood pool imaging failed to detect a shift in blood volume with oral 5-ISMN administration at any dose tested in normal dogs and dogs with CHF, despite adequate drug absorption. On the basis of the results of this study, 5-ISMN may not be beneficial in the treatment of dogs with CHF.