The Effect of Ramipril on Left Ventricular Mass, Myocardial Fibrosis, Diastolic Function, and Plasma Neurohormones in Maine Coon Cats with Familial Hypertrophic Cardiomyopathy without Heart Failure

Advancing Treatments for Feline Hypertrophic Cardiomyopathy: The Role of Animal Models and Targeted Therapeutics

Feline HCM is the most common cardiovascular disease in cats, leading to devastating outcomes, including congestive heart failure (CHF), arterial thromboembolism (ATE), and sudden death. Evidence demonstrating long-term survival benefit with currently available therapies is lacking. Therefore, it is imperative to explore intricate genetic and molecular pathways that drive HCM pathophysiology to inspire the development of novel therapeutics. Several clinical trials exploring new drug therapies are currently underway, including those investigating small molecule inhibitors and rapamycin. This article outlines the key work performed using cellular and animal models that has led to and continues to guide the development of new innovative therapeutic strategies.

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.

Circulating renin‐angiotensin‐aldosterone system activity in cats with systemic hypertension or cardiomyopathy

Background

Activity of the circulating renin‐angiotensin‐aldosterone system (RAAS) has not been comprehensively characterized in cats with systemic hypertension (SH) or cardiomyopathy (CM), and the effects of furosemide or amlodipine treatment on the RAAS have not been fully evaluated in cats.

Hypothesis/Objectives

To document RAAS activity in cats with SH or CM compared to healthy cats and determine how RAAS profiles change with furosemide or amlodipine treatment.

Animals

Sixty‐six client‐owned cats: 15 with SH (7 amlodipine‐treated, 8 untreated), 17 with advanced CM (7 furosemide‐treated, 10 not furosemide‐treated), and 34 healthy cats.

Methods

Equilibrium concentrations of RAAS peptides and aldosterone were quantified in serum samples by liquid chromatography‐mass spectrometry. Variables were compared between groups using Kruskal‐Wallis analysis with post hoc Holms‐corrected Dunn's testing.

Results

Compared with healthy cats, cats with CM had higher concentrations of angiotensin I, aldosterone, and plasma renin activity (all P < .01), and these differences remained significant (P < .03) after considering subgroups of untreated or furosemide‐treated cats. Compared with healthy cats, untreated cats with SH showed no differences in RAAS biomarkers, whereas amlodipine‐treated cats had higher concentrations of angiotensins I, II, III, IV, and 1‐7, aldosterone, and plasma renin activity (all P < .03). Multivariable analysis determined that furosemide and amlodipine treatments were independent predictors of increased RAAS biomarker concentrations.

Conclusions and Clinical Importance

Cats with CM had increased RAAS activity, whereas cats with untreated SH did not. Furosemide and amlodipine both led to nonspecific activation of both classical and alternative RAAS pathways in cats.

The Feline Cardiomyopathies: 2. Hypertrophic cardiomyopathy

Practical relevance:

Hypertrophic cardiomyopathy (HCM) is the most common form of feline cardiomyopathy observed clinically and may affect up to approximately 15% of the domestic cat population, primarily as a subclinical disease. Fortunately, severe HCM, leading to heart failure or arterial thromboembolism (ATE), only occurs in a small proportion of these cats.

Patient group:

Domestic cats of any age from 3 months upward, of either sex and of any breed, can be affected. A higher prevalence in male and domestic shorthair cats has been reported.

Diagnostics:

Subclinical feline HCM may or may not produce a heart murmur or gallop sound. Substantial left atrial enlargement can often be identified radiographically in cats with severe HCM. Biomarkers should not be relied on solely to diagnose the disease. While severe feline HCM can usually be diagnosed via echocardiography alone, feline HCM with mild to moderate left ventricular (LV) wall thickening is a diagnosis of exclusion, which means there is no definitive test for HCM in these cats and so other disorders that can cause mild to moderate LV wall thickening (eg, hyperthyroidism, systemic hypertension, acromegaly, dehydration) need to be ruled out.

Key findings:

While a genetic cause of HCM has been identified in two breeds and is suspected in another, for most cats the cause is unknown. Systolic anterior motion of the mitral valve (SAM) is the most common cause of dynamic left ventricular outflow tract obstruction (DLVOTO) and, in turn, the most common cause of a heart murmur with feline HCM. While severe DLVOTO is probably clinically significant and so should be treated, lesser degrees probably are not. Furthermore, since SAM can likely be induced in most cats with HCM, the distinction between HCM without obstruction and HCM with obstruction (HOCM) is of limited importance in cats. Diastolic dysfunction, and its consequences of abnormally increased atrial pressure leading to signs of heart failure, and sluggish atrial blood flow leading to ATE, is the primary abnormality that causes clinical signs and death in affected cats. Treatment (eg, loop diuretics) is aimed at controlling heart failure. Preventive treatment (eg, antithrombotic drugs) is aimed at reducing the risk of complications (eg, ATE).

Conclusions:

Most cats with HCM show no overt clinical signs and live a normal or near-normal life despite this disease. However, a substantial minority of cats develop overt clinical signs referable to heart failure or ATE that require treatment. For most cats with clinical signs caused by HCM, the long-term prognosis is poor to grave despite therapy.

Areas of uncertainty:

Genetic mutations (variants) that cause HCM have been identified in a few breeds, but, despite valiant efforts, the cause of HCM in the vast majority of cats remains unknown. No treatment currently exists that reverses or even slows the cardiomyopathic process in HCM, again despite valiant efforts. The search goes on.

Multiple corticosteroid abnormalities in cats with hyperaldosteronism

Background

The frequency with which multiple corticosteroid abnormalities occur in cats with aldosterone secreting adrenocortical tumors is unknown.

Objectives

To evaluate adrenal‐derived corticosteroids in cats in which blood samples were submitted for measure of aldosterone.

Animals

Two hundred ninety‐seven cats.

Methods

Retrospective study. Analysis of a convenience sample of previously submitted serum or plasma. Progesterone, corticosterone, and cortisol were measured in feline serum or plasma samples submitted to an endocrinology laboratory for aldosterone measurements. Demographics and clinical history were retrieved from submittal forms when provided. Statistical testing was performed to investigate associations among the adrenal corticosteroids.

Results

Progesterone and corticosterone concentrations were strongly correlated (ρ = 0.74; P < .001). Progesterone (median, 5 nmol/L; interquartile range, 3‐10 nmol/L) and corticosterone (113 nmol/L, 38‐250 nmol/L) in cats with markedly increased aldosterone concentrations (≥3000 pmol/L) were higher than progesterone (1 nmol/L, 1‐2 nmol/L) and corticosterone (12 nmol/L, 3‐25 nmol/L) in cats with normal aldosterone concentrations (P < .001 for both comparisons). Progesterone concentrations ≥10 nmol/L (normal, ≤2 nmol//L) occurred in 24 of 76 (32%) cats with aldosterone concentrations ≥3000 pmol/L. Cortisol was lower in cats with aldosterone concentrations ≥3000 pmol/L as compared to those with aldosterone concentrations <500 pmol/L (59 nmol/L, 27‐103 nmol/L vs 103 nmol/L, 49‐182 nmol/L; P = .002).

Conclusions and Clinical Importance

Multiple corticosteroid abnormalities occur in a subset of cats with hyperaldosteronism. The magnitude of increases in progesterone and corticosterone in some cats with hyperaldosteronism is likely to be clinically relevant.

Effect of angiotensin receptor blockers and angiotensin-converting enzyme 2 on plasma equilibrium angiotensin peptide concentrations in cats with heart disease

Background

Little is known about the effect of renin angiotensin aldosterone system‐inhibiting (RAASi) drugs on alternative angiotensin peptides (APs) such as angiotensin 1‐7 (Ang1‐7), which are mediated by angiotensin‐converting enzyme 2 (ACE2).

Hypothesis/Objectives

Angiotensin receptor blockers (ARBs) would alter balance of APs and differences would be magnified in vitro by incubation of plasma samples with recombinant human ACE2 (rhACE2).

Animals

Six cats with cardiomyopathy (CM), 8 healthy cats.

Methods

Prospective open label trial. Plasma equilibrium concentrations of APs were measured in healthy cats as well as in CM cats that first received no RAASi drugs (CM_noRAASi) and then after 14 days of PO telmisartan (CM_ARB). Plasma APs also were measured after in vitro incubation with rhACE2.

Results

No significant differences were found between healthy and CM_noRAASi groups. Concentrations of several APs, including angiotensin I (AT1) and angiotensin II (AT2) were significantly different between CM_noRAASi and CM_ARB groups. Incubation with rhACE2 decreased AT1 and AT2 in both groups. The geometric mean concentration of Ang1‐7 was significantly higher in CM_ARB (4.9 pg/mL; 95% confidence interval [CI], 3.7‐6.4 pg/mL) vs CM_noRAASi (3.2 pg/mL; 95% CI, 2.2‐4.7 pg/mL; P = .01) and in CM_ARB + ACE2 (5.0 pg/mL; 95% CI, 3.9‐6.4 pg/mL) vs CM_noRAASi + ACE2 (3.0 pg/mL; 95% CI, 1.7‐5.5 pg/mL; P = .01). The most favorable theoretical AP profile that maximized Ang1‐7 and other alternative APs was CM_ARB + ACE2.

Conclusions and Clinical Importance

Balance between traditional and alternative APs can be favorably shifted using ARBs and in vitro incubation with rhACE2. These data shed light on new AP‐targeting strategies in cats with CM.

ACVIM consensus statement guidelines for the classification, diagnosis, and management of cardiomyopathies in cats

Cardiomyopathies are a heterogeneous group of myocardial disorders of mostly unknown etiology, and they occur commonly in cats. In some cats, they are well‐tolerated and are associated with normal life expectancy, but in other cats they can result in congestive heart failure, arterial thromboembolism or sudden death. Cardiomyopathy classification in cats can be challenging, and in this consensus statement we outline a classification system based on cardiac structure and function (phenotype). We also introduce a staging system for cardiomyopathy that includes subdivision of cats with subclinical cardiomyopathy into those at low risk of life‐threatening complications and those at higher risk. Based on the available literature, we offer recommendations for the approach to diagnosis and staging of cardiomyopathies, as well as for management at each stage.

Evaluation of benazepril in cats with heart disease in a prospective, randomized, blinded, placebo-controlled clinical trial

Background

Heart disease is an important cause of morbidity and mortality in cats, but there is limited evidence of the benefit of any medication.

Hypothesis

The angiotensin‐converting enzyme inhibitor benazepril would delay the time to treatment failure in cats with heart disease of various etiologies.

Animals

One hundred fifty‐one client‐owned cats.

Methods

Cats with heart disease, confirmed by echocardiography, with or without clinical signs of congestive heart failure, were recruited between 2002 and 2005 and randomized to benazepril or placebo in a prospective, multicenter, parallel‐group, blinded clinical trial. Benazepril (0.5‐1.0 mg/kg) or placebo was administered PO once daily for up to 2 years. The primary endpoint was treatment failure. Analyses were conducted separately for all‐cause treatment failure (main analysis) and heart disease‐related treatment failure (supportive analysis).

Results

No benefit of benazepril versus placebo was detected for time to all‐cause treatment failure (P = .42) or time to treatment failure related to heart disease (P = .21). Hazard ratios (95% confidence interval [CI]) from multivariate analysis for benazepril compared with placebo were 1.00 (0.57‐1.74) for all‐cause failure, and 0.99 (0.50‐1.94) for forward selection and 0.93 (0.48‐1.81) for bidirectional selection models for heart disease‐related failure. There were no significant differences between groups over time after administration of the test articles in left atrium diameter, left ventricle wall thickness, quality of life scores, adverse events, or plasma biochemistry or hematology variables.

Conclusions and Clinical Relevance

Benazepril was tolerated well in cats with heart disease, but no evidence of benefit was detected.

Anatomical assessment of intrathoracic cardiovascular structures using fast spin-echo double inversion recovery and steady-state free precession magnetic resonance imaging in a normal cat

In human medicine, non-contrast cardiac magnetic resonance imaging (CMRI) is routinely used to assess the cardiovascular system. In this study, using non-contrast CMRI, we provide a thorough description of the normal appearance of the intrathoracic cardiovascular structures in one healthy cat using a magnet operating at a field of 1.5-Tesla. The CMRI protocol was based on the use of fast spin-echo double inversion recovery and steady-state free precession pulse sequences in oblique short-axis, vertical long-axis, and horizontal long-axis imaging planes. After imaging the feline heart, four cadaver cats injected with latex substance into their arterial and venous systems were sectioned to facilitate interpretation of the intrathoracic cardiovascular structures to the corresponding CMRI. The fast spin-echo double inversion recovery images showed the best evaluation of gross intrathoracic anatomy, giving excellent contrast of the myocardium and vessels walls as they appeared with intermediate signal intensity compared to the lumen that appeared with low signal intensity. By contrast, steady-state free precession images showed details of the heart cavities and vascular lumen due to the high signal intensity of fast-flowing blood. The results of this study provide some anatomic detail for the heart and associated vessels as seen by non-contrast CMRI in the domestic cat.

The renin-angiotensin-aldosterone system and its suppression

Chronic activation of the renin-angiotensin-aldosterone system (RAAS) promotes and perpetuates the syndromes of congestive heart failure, systemic hypertension, and chronic kidney disease. Excessive circulating and tissue angiotensin II (AngII) and aldosterone levels lead to a pro-fibrotic, -inflammatory, and -hypertrophic milieu that causes remodeling and dysfunction in cardiovascular and renal tissues. Understanding of the role of the RAAS in this abnormal pathologic remodeling has grown over the past few decades and numerous medical therapies aimed at suppressing the RAAS have been developed. Despite this, morbidity from these diseases remains high. Continued investigation into the complexities of the RAAS should help clinicians modulate (suppress or enhance) components of this system and improve quality of life and survival. This review focuses on updates in our understanding of the RAAS and the pathophysiology of AngII and aldosterone excess, reviewing what is known about its suppression in cardiovascular and renal diseases, especially in the cat and dog.

Antihypertensive treatment with telmisartan in a cat with amlodipine-induced gingival hyperplasia

Case summary

Systemic arterial hypertension is commonly reported in middle-aged-to-older cats. Amlodipine is recommended as the initial antihypertensive drug in cats. In this case report, gingival hyperplasia secondary to the use of amlodipine in a cat is described. Benazepril as a monotherapy was unsuccessful in reducing blood pressure in this cat. After replacement of benazepril by telmisartan, gingival hyperplasia disappeared and blood pressure was well controlled.

Relevance and novel information

This case report describes the first reported case of reversible gingival hyperplasia as a result of the treatment with amlodipine. It also contains the first published data on the effect of telmisartan in a hypertensive cat.

Genetics and Genomics of Single-Gene Cardiovascular Diseases: Common Hereditary Cardiomyopathies as Prototypes of Single-Gene Disorders

This is the first of 2 review papers on genetics and genomics appearing as part of the series on "omics." Genomics pertains to all components of an organism's genes, whereas genetics involves analysis of a specific gene or genes in the context of heredity. The paper provides introductory comments, describes the basis of human genetic diversity, and addresses the phenotypic consequences of genetic variants. Rare variants with large effect sizes are responsible for single-gene disorders, whereas complex polygenic diseases are typically due to multiple genetic variants, each exerting a modest effect size. To illustrate the clinical implications of genetic variants with large effect sizes, 3 common forms of hereditary cardiomyopathies are discussed as prototypic examples of single-gene disorders, including their genetics, clinical manifestations, pathogenesis, and treatment. The genetic basis of complex traits is discussed in a separate paper.

Feline Congestive Heart Failure: Current Diagnosis and Management

Congestive heart failure (CHF) is a well-known disorder in feline practice, having been recognized as the most common clinical syndrome in cats with hypertrophic cardiomyopathy, for example. This article identifies the reasons why an accurate diagnosis of CHF is important and the means by which to obtain one; pharmacologic and nonpharmacologic methods for controlling signs of CHF; and recommendations for follow-up evaluations, monitoring, and troubleshooting.

Management of asymptomatic (occult) feline cardiomyopathy: Challenges and realities

BACKGROUND

Cardiomyopathy distinguishes a heterogeneous group of myocardial disorders that represent the most prevalent cause of feline heart disease. Etiology is uncertain and the natural history is presently unresolved. Hypertrophic cardiomyopathy is the most common of these conditions, and while the majority of affected cats are asymptomatic, a proportion is at risk to develop serious morbidities--the most devastating of which include congestive heart failure, arterial thromboembolism, and cardiac death. Predicting when or whether an asymptomatic cat might develop morbidity is hindered by lack of evidence-based clinical trials. Superimposed, these issues create an irresolvable predicament that presently confounds medical decision-making.

METHODS

Review of current perspectives for managing asymptomatic (occult) feline cardiomyopathy.

RESULTS

Complex pathophysiology and (likely) sarcomeric mutations give rise to heterogeneous cardiac phenotypes and variable clinical findings. Echocardiography remains the gold standard to clarify cardiac morphology. Frequently, however, detection of echocardiographic alterations--though often of unproven clinical significance--extrapolates by inference or implication a specter of disease, and with this, leads to a path of long-term treatment and testing. Presently, there is no proof that any particular therapy reduces morbidity or prolongs survival of cats affected with occult cardiomyopathy. Recently, however, evidence has accumulated to support the belief that certain prognostic indicators suggest risk for poor outcome. Accordingly, and in absence of evidence-based clinical trials, current practice has shifted to view therapy with the intent to target pathophysiology underlying documented or perceived clinical markers, whose presence portends high risk in certain patients. Affected animals and potentially siblings should be monitored using clinical testing that also takes into account age-related comorbidities.

CONCLUSIONS

Asymptomatic (occult) feline cardiomyopathy includes complex and heterogeneous diseases whose outcomes are challenging to predict. Review of available evidence-based treatment data leaves no uncertainties regarding drugs with established efficacy. There presently are none. Current management focuses upon identification of documented risk factors, individualized and tailored therapy, and cogent monitoring. Drugs most commonly considered in this paradigm include those that might reduce thromboembolic risk in cases with substantial left atrial enlargement or dysfunction, agents to counteract left ventricular remodeling, or medications that ameliorate systolic or diastolic dysfunction. Discovering reliable prognostic indicators may further improve stratification to identify patients at highest risk, or detect subsets that respond favorably. These issues shape the challenge to identify sensible preventative management and cost-effective, long-term monitoring strategies.

Pharmacodynamics of alacepril in healthy cats

Objectives The aims of this study were to investigate the pharmacodynamics of alacepril and to determine the appropriate dose for clinical usage in cats. Methods Six experimental cats were used. Each cat received alacepril orally at a single dose of 1 mg/kg, 2 mg/kg and 3 mg/kg. Blood samples were collected before administration and at 2, 4, 6, 8, 12, 24, 36, 48 and 72 h after administration to measure serum angiotensin converting enzyme (ACE) activity. Systolic blood pressure was also measured at the same time point. Results Dose-dependent inhibition of ACE activity was observed. Doses of 2 mg/kg and 3 mg/kg alacepril were considered to effectively inhibit ACE activity. There were no significant differences in systolic blood pressue among groups at any time point. Conclusions and relevance Alacepril 2-3 mg/kg q24h may be an appropriate dosage for clinical use in cats.

Myocardial collagen deposition and inflammatory cell infiltration in cats with pre-clinical hypertrophic cardiomyopathy

The histological features of feline hypertrophic cardiomyopathy (HCM) have been well documented, but there are no reports describing the histological features in mild pre-clinical disease, since cats are rarely screened for the disease in the early stages before clinical signs are apparent. Histological changes at the early stage of the disease in pre-clinical cats could contribute to an improved understanding of disease aetiology or progression. The aim of this study was to evaluate the histological features of HCM in the left ventricular (LV) myocardium of cats diagnosed with pre-clinical HCM. Clinically healthy cats with normal (n = 11) and pre-clinical HCM (n = 6) were identified on the basis of echocardiography; LV free wall dimensions (LVFWd) and/or interventricular septal wall (IVSd) dimensions during diastole of 6-7 mm were defined as HCM, while equivalent dimensions <5.5 mm were defined as normal. LV myocardial sections were assessed and collagen content and inflammatory cell infiltrates were quantified objectively. Multifocal areas of inflammatory cell infiltration, predominantly lymphocytes, were observed frequently in the left myocardium of cats with pre-clinical HCM. Tissue from cats with pre-clinical HCM also had a higher number of neutrophils and a greater collagen content than the myocardium of normal cats. The myocardium variably demonstrated other features characteristic of HCM, including arteriolar mural hypertrophy and interstitial fibrosis and, to a lesser extent, myocardial fibre disarray and cardiomyocyte hypertrophy. These results suggest that an inflammatory process could contribute to increased collagen content and the myocardial fibrosis known to be associated with HCM.

Aldosterone breakthrough with benazepril in furosemide-activated renin-angiotensin-aldosterone system in normal dogs

Pilot studies in our laboratory revealed that furosemide-induced renin-angiotensin-aldosterone system (RAAS) activation was not attenuated by the subsequent co-administration of benazepril. This study was designed to evaluate the effect of benazepril on angiotensin-converting enzyme (ACE) activity and furosemide-induced circulating RAAS activation. Our hypothesis was that benazepril suppression of ACE activity would not suppress furosemide-induced circulating RAAS activation, indicated by urinary aldosterone concentration. Ten healthy hound dogs were used in this study. The effect of furosemide (2 mg/kg p.o., q12h; Group F; n = 5) and furosemide plus benazepril (1 mg/kg p.o., q24h; Group FB; n = 5) on circulating RAAS was determined by plasma ACE activity, 4-6 h posttreatment, and urinary aldosterone to creatinine ratio (UAldo:C) on days -1, -2, 1, 3, and 7. There was a significant increase in the average UAldo:C (μg/g) after the administration of furosemide (Group F baseline [average of days -1 and -2] UAldo:C = 0.41, SD 0.15; day 1 UAldo:C = 1.1, SD 0.56; day 3 UAldo:C = 0.85, SD 0.50; day 7 UAldo:C = 1.1, SD 0.80, P < 0.05). Benazepril suppressed ACE activity (U/L) in Group FB (Group FB baseline ACE = 16.4, SD 4.2; day 1 ACE = 3.5, SD 1.4; day 3 ACE = 1.6, SD 1.3; day 7 ACE = 1.4, SD 1.4, P < 0.05) but did not significantly reduce aldosterone excretion (Group FB baseline UAldo:C = 0.35, SD 0.16; day 1 UAldo:C = 0.79, SD 0.39; day 3 UAldo:C 0.92, SD 0.48, day 7 UAldo:C = 0.99, SD 0.48, P < 0.05). Benazepril decreased plasma ACE activity but did not prevent furosemide-induced RAAS activation, indicating aldosterone breakthrough (escape). This is particularly noteworthy in that breakthrough is observed at the time of initiation of RAAS suppression, as opposed to developing after months of therapy.

Disease pathways and novel therapeutic targets in hypertrophic cardiomyopathy

As described in earlier reviews in this series on the molecular basis of hypertrophic cardiomyopathy (HCM), HCM is one of the archetypal monogenic cardiovascular disorders to be understood at the molecular level. Twenty years after the discovery of the first HCM disease gene, genetic studies still confirm that HCM is principally a disease of the sarcomere. At the biophysical level, myofilament mutations generally enhance Ca(2+) sensitivity, maximal force production, and ATPase activity. These defects ultimately appear to converge on energy deficiency and altered Ca(2+) handling as major common paths leading to the anatomic (hypertrophy, myofiber disarray, and fibrosis) and functional features (pathological signaling and diastolic dysfunction) characteristic of HCM. In this review, we provide an account of the consequences of HCM mutations and describe how specifically targeting these molecular features has already yielded early promise for novel therapies for HCM. Although substantial efforts are still required to understand the molecular link between HCM mutations and their clinical consequences, HCM endures as an exemplar of how novel insights derived from molecular characterization of Mendelian disorders can inform the understanding of biological processes and translate into rational therapies.

Is Treatment of Feline Hypertrophic Cardiomyopathy Based in Science or Faith?

Practical relevance Feline hypertrophic cardiomyopathy (HCM) is the most common cardiac disease of cats. Treatment of HCM is usually directed at controlling signs of congestive heart failure (CHF), preventing occurrence or recurrence of systemic thromboembolism or delaying/preventing/reversing progression of subclinical disease.

Study objective and design Despite the laudable goals of therapy, however, little objective evidence supporting therapeutic decisions has been published. We, therefore, hypothesized that cardiologists base their treatment strategies on information other than published clinically relevant science. To gain insight into therapeutic decisions that cardiologists and clinicians with an interest in cardiology (n = 99) make for cats with HCM, and on what information they base these decisions, we presented participants with, and asked them to select therapy for, 12 hypothetical scenarios of HCM (± CHF). Responses and justifications for treatment choices were compiled and compared with the results of a comprehensive literature search for published information about treatment of feline HCM.

Findings Evaluation of the therapeutic strategies chosen for these hypothetical cases of HCM suggests that cardiologists or clinicians with a strong interest in cardiology often prescribe treatments knowing that little documented evidence supports their decisions.

Feline myocardial disease 2: diagnosis, prognosis and clinical management

Clinical challenges The diagnosis, prognosis and clinical management of feline myocardial disease (cardiomyopathy, CM) represent controversial areas in veterinaty cardiology. Diagnosis is challenging primarily because of the complex classification of feline CM, which is based on a variety of structural and functional phenotypes. Similarly, prognosis is strongly dependent on the underlying aetiology and stage of the disease, which are often unrecognised. These challenges underline the importance of a thonaugh clinical evaluation of the patient and understanding of the underlying pathophysiological mechanisms in order to select the most appropriate treatment and provide the highest standards of care.

Patient group Although a genetic predisposition has been demonstrated in some feline pedigrees (ie, Maine Coons, Ragdolls), CM can potentially affect all breeds and different age groups.

Audience General practitioners, as well as specialists in small animal medicine, cardiology and pathology, deal with feline CM cases on a regular basis.

Diagnostics Diagnosis of feline CM is primarily based on echocardiographic examination. However, even the most sophisticated techniques present important limitations because they do not necessarily identify the primary cause of the disease or recognise the precise origin of an end-stage myocardial disease. Thoracic radiography remains one of the most useful tools for identifying changes consistent with congestive heart failure. Novel diagnostic techniques include cardiac magnetic resonance imaging, positron emission tomography and genetic tests.

Evidence base Although knowledge of feline CM remains fairly rudimentary, important discoveries have been made in the past few years. Evidence-based studies have significantly improved understanding of genetic predisposition, biomarkers and response to pharmacological treatments. Hopefully, many of the unsolved questions raised in this article will find a definitive answer in the near future.

Evaluation of the renin-angiotensin system in cardiac tissues of cats with pressure-overload cardiac hypertrophy

OBJECTIVE

To clarify regulation of the renin-angiotensin (RA) system in cardiac tissues by measuring angiotensin-converting enzyme (ACE) and chymase activities in cats with pressure-overload cardiac hypertrophy.

ANIMALS

13 adult cats.

PROCEDURES

Pressure-overload cardiac hypertrophy was induced by coarctation of the base of the ascending aorta in 6 cats, and 7 cats served as untreated control animals. Cats were examined before and 3 months and 2 years after surgery. Two years after surgery, cardiac hypertrophy was confirmed by echocardiography, and the blood pressure gradient was measured at the site of constriction. Cats were euthanized, and ACE and chymase activities were measured in cardiac tissues.

RESULTS

Mean +/- SD pressure gradient across the aortic constriction was 63 +/- 6 mm Hg. Chymase activity predominated (75% to 85%) in the RA system of the cardiac tissues of cats. Fibrosis in the wall of the left ventricle was detected in cats with hypertrophy, and fibrosis of the papillary muscle was particularly evident.

CONCLUSIONS AND CLINICAL RELEVANCE

Chronic pressure overload on the heart of cats can activate the RA system in cardiac tissues. A local increase in angiotensin II was one of the factors that sustained myocardial remodeling.