Echocardiographic screening of purebred cats: an overview from 2002 to 2005

Classification of feline hypertrophic cardiomyopathy-associated gene variants according to the American College of Medical Genetics and Genomics guidelines

Introduction

The correct labeling of a genetic variant as pathogenic is important as breeding decisions based on incorrect DNA tests can lead to the unwarranted exclusion of animals, potentially compromising the long-term health of a population. In human medicine, the American college of Medical Genetics (ACMG) guidelines provide a framework for variant classification. This study aims to apply these guidelines to six genetic variants associated with hypertrophic cardiomyopathy (HCM) in certain cat breeds and to propose a modified criterion for variant classification.

Methods

Genetic samples were sourced from five cat breeds: Maine Coon, Sphynx, Ragdoll, Devon Rex, and British Short- and Longhair. Allele frequencies were determined, and in the subset with phenotypes available, odds ratios to determine the association with HCM were calculated. In silico evaluation followed with joint evidence and data from other publications assisting in the classification of each variant.

Results

Two variants, MYBPC3:c.91G > C [A31P] and MYBPC3:c.2453C > T [R818W], were designated as pathogenic. One variant, MYH7:c.5647G > A [E1883K], was found likely pathogenic, while the remaining three were labeled as variants of unknown significance.

Discussion

Routine genetic testing is advised solely for the MYBPC3:c.91G > C [A31P] in the Maine Coon and MYBPC3:c.2453C > T [R818W] in the Ragdoll breed. The human ACMG guidelines serve as a suitable foundational tool to ascertain which variants to include; however, refining them for application in veterinary medicine might be beneficial.

Genetics of feline hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by an abnormal increase in myocardial mass that affects cardiac structure and function. HCM is the most common inherited cardiovascular disease in humans (0.2%) and the most common cardiovascular disease in cats (14.7%). Feline HCM phenotype is very similar to the phenotype found in humans, but the time frame for the development of the disease is significantly shorter. Similar therapeutic agents are used in its treatment and it has the same complications, such as heart failure, thromboembolism and sudden cardiac death. In contrast to humans, in whom thousands of genetic variants have been identified, genetic studies in cats have been limited to fragment analysis of two sarcomeric genes identifying two variants in MYBPC3 and one in MYH7. Two of these variants have also been associated with human disease. The high prevalence of the reported variants in non-affected cats hinders the assumption of their pathogenicity in heterozygotes. An in-depth review of the literature about genetic studies on feline HCM in comparison with the same disease in humans is presented here. The close similarity in the phenotype and genotype between cats and humans makes the cat an excellent model for the pathophysiological study of the disease and future therapeutic agents.

Evaluation of a sensitive cardiac troponin I assay as a screening test for the diagnosis of hypertrophic cardiomyopathy in cats

Background

Hypertrophic cardiomyopathy (HCM) is the most common cardiac disease in cats. However, most cats are not diagnosed until they develop congestive heart failure, arterial thromboembolism (ATE), or sudden cardiac death. Thus, an affordable screening test for early detection of HCM is desirable.

Hypothesis/Objectives

Evaluation of a sensitive cardiac troponin I (cTnI) assay as a screening test for HCM in cats and determination of a cutoff for its early detection.

Animals

One hundred sixty‐six client‐owned cats (male, n = 97) of various breeds were evaluated and classified using echocardiography as being healthy (n = 87), equivocal (n = 15), or having HCM (mild, n = 16; moderate, n = 10; severe, n = 34) or ATE (n = 4).

Methods

All cats were prospectively evaluated by echocardiography, and serum cTnI concentration was determined using the currently most sensitive assay (Siemens ADVIA Centaur TnI‐Ultra).

Results

The median cTnI concentration was significantly different between study groups (P < .000001). A cutoff of 0.06 ng/mL provided good discrimination between healthy cats and cats with HCM (sensitivity, 91.7%; specificity, 95.4%; area under the curve [AUC], 0.95; 95% confidence interval [CI], 0.899‐0.978). Even for asymptomatic cats with HCM, sensitivity and specificity for a cutoff of >0.06 ng/mL remained high at 87.8% and 95.4%, respectively (AUC, 0.93; 95% CI, 0.864‐0.964).

Conclusions and clinical importance

Cardiac troponin I can be used as a sensitive and specific screening test for the diagnosis of HCM in otherwise healthy cats (cutoff, >0.06 ng/mL). However, echocardiography is needed to confirm the diagnosis.

International collaborative study to assess cardiovascular risk and evaluate long-term health in cats with preclinical hypertrophic cardiomyopathy and apparently healthy cats: The REVEAL Study

Background

Hypertrophic cardiomyopathy is the most prevalent heart disorder in cats and principal cause of cardiovascular morbidity and mortality. Yet, the impact of preclinical disease is unresolved.

Hypothesis/Objectives

Observational study to characterize cardiovascular morbidity and survival in cats with preclinical nonobstructive (HCM) and obstructive (HOCM) hypertrophic cardiomyopathy and in apparently healthy cats (AH).

Animals

One thousand seven hundred and thirty client‐owned cats (430 preclinical HCM; 578 preclinical HOCM; 722 AH).

Methods

Retrospective multicenter, longitudinal, cohort study. Cats from 21 countries were followed through medical record review and owner or referring veterinarian interviews. Data were analyzed to compare long‐term outcomes, incidence, and risk for congestive heart failure (CHF), arterial thromboembolism (ATE), and cardiovascular death.

Results

During the study period, CHF, ATE, or both occurred in 30.5% and cardiovascular death in 27.9% of 1008 HCM/HOCM cats. Risk assessed at 1, 5, and 10 years after study entry was 7.0%/3.5%, 19.9%/9.7%, and 23.9%/11.3% for CHF/ATE, and 6.7%, 22.8%, and 28.3% for cardiovascular death, respectively. There were no statistically significant differences between HOCM compared with HCM for cardiovascular morbidity or mortality, time from diagnosis to development of morbidity, or cardiovascular survival. Cats that developed cardiovascular morbidity had short survival (mean ± standard deviation, 1.3 ± 1.7 years). Overall, prolonged longevity was recorded in a minority of preclinical HCM/HOCM cats with 10% reaching 9‐15 years.

Conclusions and Clinical Importance

Preclinical HCM/HOCM is a global health problem of cats that carries substantial risk for CHF, ATE, and cardiovascular death. This finding underscores the need to identify therapies and monitoring strategies that decrease morbidity and mortality.

Reference intervals and allometric scaling of two-dimensional echocardiographic measurements in 150 healthy cats

The objective of the study was to evaluate the effects of body weight (BW), breed, and sex on two-dimensional (2D) echocardiographic measures, reference ranges, and prediction intervals using allometrically-scaled data of left atrial (LA) and left ventricular (LV) size and LV wall thickness in healthy cats. Study type was retrospective, observational, and clinical cohort. 150 healthy cats were enrolled and 2D echocardiograms analyzed. LA diameter, LV wall thickness, and LV dimension were quantified using three different imaging views. The effect of BW, breed, sex, age, and interaction (BW*sex) on echocardiographic variables was assessed using univariate and multivariate regression and linear mixed model analysis. Standard (using raw data) and allometrically scaled (Y=a × M^b) reference intervals and prediction intervals were determined. BW had a significant (P<0.05) independent effect on 2D variables whereas breed, sex, and age did not. There were clinically relevant differences between reference intervals using mean ± 2SD of raw data and mean and 95% prediction interval of allometrically-scaled variables, most prominent in larger (>6 kg) and smaller (<3 kg) cats. A clinically relevant difference between thickness of the interventricular septum (IVS) and dimension of the LV posterior wall (LVPW) was identified. In conclusion, allometric scaling and BW-based 95% prediction intervals should be preferred over conventional 2D echocardiographic reference intervals in cats, in particular in small and large cats. These results are particularly relevant to screening examinations for feline hypertrophic cardiomyopathy.

Toxicity and response in cats with neoplasia treated with toceranib phosphate

Objectives

Toceranib phosphate is a tyrosine kinase inhibitor licensed for the treatment of non-resectable Patnaik grade II/III recurrent cutaneous mast cell tumours in dogs. There is no information in cats regarding the tolerated dose, toxicity or tumour response of this drug. The aim of this study was to analyse retrospectively a cohort of cats with advanced neoplasia treated with toceranib to identify toxicity and response.

Methods

The medical records of the Small Animal Teaching Hospital were reviewed. Cats were included if they had received toceranib for at least 2 weeks for the treatment of histologically or cytologically confirmed neoplastic disease, and had at least one set of monitoring blood tests (haematology, biochemistry) performed after baseline tests. Toxicity was graded according to the Veterinary Comparative Oncology Group – common terminology criteria for adverse events(VCOG-CTCAE) and response was measured according to Response Evaluation In Solid Tumors (RECIST) criteria.

Results

Fourteen cats met the inclusion criteria, the majority of which (13/14) had received previous therapy (surgery, radiotherapy, chemotherapy). The most common tumour types were mast cell tumours or malignant epithelial tumours. Toxicity occurred in 10/14 cats – 10 cats had mild myelosuppression or gastrointestinal effects. Two cats developed severe hepatoxicity. One cat died from congestive heart failure, although whether this was related to toceranib therapy is unknown. Regarding response, one cat achieved complete response; two cats achieved partial response and five cats achieved stable disease: overall biological response rate was 57.1%. All of the cats that achieved either partial or complete response were treated for mast cell disease. Overall median duration of response was 90 days (range 14–570 days). None of the cats with squamous cell carcinoma achieved a response.

Conclusions and relevance

Toceranib phosphate is generally well tolerated in cats, with toxicity limited to mild gastrointestinal or myelosuppressive effects in the majority of cases (10/14) in this study; however, hepatotoxicity is a concern. Response to treatment in this small cohort was similar to that reported in dogs.

Incidental echocardiographic findings of a quadricuspid aortic valve associated with aortic regurgitation in a cat

Case summary

A 10-month-old male domestic shorthair cat was brought to Kitanomori Animal Hospital for routine castration. Preoperative thoracic radiography revealed a mildly enlarged heart silhouette, and transthoracic echocardiography (ECHO) suggested a quadricuspid aortic valve associated with central aortic regurgitation (regurgitant fraction 31%). After sedation with intramuscular medetomidine and midazolam for castration, heart rate decreased from 193 to 76 beats per minute. ECHO under sedation revealed two equally small and two equally large aortic valve cusps, suggesting a type C quadricuspid aortic valve. The findings were confirmed by real-time three-dimensional ECHO.

Relevance and novel information

This case reveals the echocardiographic features of a feline quadricuspid aortic valve and shows that transthoracic ECHO is useful to examine aortic valve morphology in cats. It also suggests that echocardiographic screening may be beneficial for detecting congenital cardiac anomalies in apparently healthy cats.

Comparison of auscultatory and echocardiographic findings in healthy adult cats

OBJECTIVES

This pilot study was performed to investigate murmur prevalence and to explore the association between auscultatory and echocardiographic findings in apparently healthy cats in order to design a larger study.

ANIMALS, MATERIALS AND METHODS

Adult cats in 4 rehoming centres were screened by auscultation and echocardiography (echo) over 2 periods of 2 weeks each. In the first period, echo was attempted only in cats with murmurs. In the second period, all cats underwent auscultation by 2 observers and echo. LVH was defined in 5 ways: maximal diastolic left ventricular (LV) wall thickness ≥ 6 mm or ≥ 5.5 mm with 2D (LVH(6 2D), LVH(5.5 2D), respectively) or M-Mode echo (LVH(6 MM) or LVH(5.5 MM) respectively), or LV wall thickness ≥ 6 mm (2D) for >50% of a wall segment (LVH(50%)).

RESULTS

67/199 (34%) cats had a murmur. Interobserver agreement on murmur presence was moderate (κ 0.47). 61 cats with a murmur and 31 cats without underwent both auscultation and echo. Depending on the criteria, LVH was present in 31 (LVH(6 2D)), 21 (LVH(50%)) and 11 (LVH(6 MM)) scanned cats. 18-62% of cats with murmurs had LVH, depending on the echo criteria used. Agreement was best between observers in identifying LVH using LVH(6 2D) and LVH(50%) (κ = 1.0).

CONCLUSIONS

Heart murmurs are common in apparently healthy cats. The prevalence of LVH varies depending on the criteria used.