Long-term Outcome of Irish Wolfhound Dogs with Preclinical Cardiomyopathy, Atrial Fibrillation, or Both Treated with Pimobendan, Benazepril Hydrochloride, or Methyldigoxin Monotherapy

Basic triage in dogs and cats: Part I

Background

Emergency cases can present at any time of the day or night. All small animal practitioners need to have the skills to triage and stabilize common emergency cases even if they ultimately aim to refer the patient to another facility.

Objectives and procedures

The first part of this 3-part review article series covers respiratory distress and seizures. A stepwise approach to categorize and stabilize these cases is outlined, along with helpful tips to optimize the referral experience, if indicated.

Results

Having a strong methodical approach to animals in respiratory distress optimizes treatment. Similarly, achieving cessation of seizures, along with having a good understanding of the causes of seizures, allows for patient stabilization.

Conclusion and clinical relevance

Do NOT refer emergent cases before completing basic stabilization. Many emergency cases do not require emergent referral and can be worked up by the primary veterinarian or sent to a referral clinic on an appointment basis after appropriate stabilization steps are completed.

Genetic Basis of Dilated Cardiomyopathy in Dogs and Its Potential as a Bidirectional Model

Simple Summary

Heart disease is a leading cause of death for both humans and dogs. Inherited heart diseases, including dilated cardiomyopathy (DCM), account for a proportion of these cases. Human and canine patients with DCM suffer from an enlarged heart that can no longer pump efficiently, resulting in heart failure. This causes symptoms or clinical signs like difficulty breathing, irregular heartbeat, and eventually death. The symptoms or clinical signs of this disease vary in age of onset at the beginning of symptoms, sex predisposition, and overall disease progression. Despite the many similarities in DCM in both species, only a few candidate genes so far have been linked to this disease in dogs versus tens of genes identified in human DCM. Additionally, the use of induced pluripotent stem cells, or engineered stem cells, has been widely used in the study of human genetic heart disease but has not yet been fully adapted to study heart disease in dogs. This review describes the current knowledge on the genetics and subtypes of naturally occurring DCM in dogs, and how advances in research might benefit the dog but also the human patient. Additionally, a novel method using canine engineered stem cells to uncover unknown contributions of mistakes in DNA to the progression of DCM will be introduced along with its applications for human DCM disease modeling and treatment.

Abstract

Cardiac disease is a leading cause of death for both humans and dogs. Genetic cardiomyopathies, including dilated cardiomyopathy (DCM), account for a proportion of these cases in both species. Patients may suffer from ventricular enlargement and systolic dysfunction resulting in congestive heart failure and ventricular arrhythmias with high risk for sudden cardiac death. Although canine DCM has similar disease progression and subtypes as in humans, only a few candidate genes have been found to be associated with DCM while the genetic background of human DCM has been more thoroughly studied. Additionally, experimental disease models using induced pluripotent stem cells have been widely adopted in the study of human genetic cardiomyopathy but have not yet been fully adapted for the in-depth study of canine genetic cardiomyopathies. The clinical presentation of DCM is extremely heterogeneous for both species with differences occurring based on sex predisposition, age of onset, and the rate of disease progression. Both genetic predisposition and environmental factors play a role in disease development which are identical in dogs and humans in contrast to other experimental animals. Interestingly, different dog breeds have been shown to develop distinct DCM phenotypes, and this presents a unique opportunity for modeling as there are multiple breed-specific models for DCM with less genetic variance than human DCM. A better understanding of DCM in dogs has the potential for improved selection for breeding and could lead to better overall care and treatment for human and canine DCM patients. At the same time, progress in research made for human DCM can have a positive impact on the care given to dogs affected by DCM. Therefore, this review will analyze the feasibility of canines as a naturally occurring bidirectional disease model for DCM in both species. The histopathology of the myocardium in canine DCM will be evaluated in three different breeds compared to control tissue, and the known genetics that contributes to both canine and human DCM will be summarized. Lastly, the prospect of canine iPSCs as a novel method to uncover the contributions of genetic variants to the pathogenesis of canine DCM will be introduced along with the applications for disease modeling and treatment.

Pharmacokinetics of pimobendan following oral administration to New Zealand White rabbits (Oryctolagus cuniculus)

OBJECTIVE

To determine the pharmacokinetics and potential adverse effects of pimobendan after oral administration in New Zealand White rabbits (Ocytolagus cuniculi).

ANIMALS

10 adult sexually intact (5 males and 5 females) rabbits.

PROCEDURES

2 pilot studies were performed with a pimobendan suspension or oral tablets. Eight rabbits received 7.5 mg of pimobendan (mean 2.08 mg/kg) suspended in a critical care feeding formula. Plasma concentrations of pimobendan and O-demethylpimobendan (ODMP) were measured, and pharmacokinetic parameters were calculated for pimobendan by noncompartmental analysis. Body weight, food and water consumption, mentation, urine, and fecal output were monitored.

RESULTS

Mean ± SD maximum concentration following pimobendan administration was 15.7 ± 7.54 ng/mL and was detected at 2.79 ± 1.25 hours. The half-life was 3.54 ± 1.32 hours. Plasma concentrations of pimobendan were detectable for up to 24 hours. The active metabolite, ODMP, was detected in rabbits for 24 to 36 hours. An adverse event occurred following administration of pimobendan in tablet form in 1 pilot study, resulting in death secondary to aspiration. No other adverse events occurred.

CLINICAL RELEVANCE

Plasma concentrations of pimobendan were lower than previously reported for dogs and cats, despite administration of higher doses, and had longer time to maximum concentration and half-life. Based on this study, 2 mg/kg of pimobendan in a critical care feeding formulation should maintain above a target plasma concentration for 12 to 24 hours. However, further studies evaluating multiple-dose administration as well as pharmacodynamic studies and clinical trials in rabbits with congestive heart failure are needed to determine accurate dose and frequency recommendations.

Prevalence of sudden cardiac death in dogs with atrial fibrillation

Background

Atrial fibrillation (AF) is associated with increased risk of sudden cardiac death (SCD) in humans, independent of secondary risk factors such as thrombogenic disorders. In dogs, SCD is described in a number of heart diseases, but an association between AF and SCD is unreported.

Hypothesis

(a) A higher proportion of dogs with AF will experience SCD, and (b) SCD will be associated with complex ventricular arrhythmias.

Animals

One‐hundred forty‐two dogs with AF, and 127 dogs without AF.

Methods

Retrospective, multicenter, case‐control study. Dogs included in the AF group were compared to a control group of dogs in sinus rhythm, matched for echocardiographic diagnosis. Descriptive statistics were used to identify proportions of each group suffering SCD, compared using chi‐squared testing. Risk factors for SCD in dogs with AF were evaluated at the univariable and multivariable level using binary logistic regression. Significance was P < .05.

Results

A significantly higher proportion of dogs with AF suffered SCD than dogs in the control group (14.8% vs 5.5%; P = .01). Younger age at diagnosis, larger left atrial size, and a history of syncope all were independent predictors of SCD in dogs with AF (χ², 16.3; P = .04).

Conclusions and Clinical Importance

Atrial fibrillation was associated with a higher prevalence of SCD in dogs. A history of syncope may be a useful predictor of SCD risk.

Clinical and pathological findings in rabbits with cardiovascular disease: 59 cases (2001-2018)

OBJECTIVE

To determine epidemiological features of cardiovascular disease in rabbits examined at a veterinary teaching hospital and characterize clinical and pathological findings.

ANIMALS

59 rabbits.

PROCEDURES

Medical records from 2001 to 2018 were reviewed, and data were collected. Echocardiographic images and histologic diagnoses were reviewed.

RESULTS

The prevalence of cardiovascular disease was 2.6% (59/2,249). Clinical signs related to cardiac disease included heart murmur (n = 25 rabbits), arrhythmia (22), tachypnea or dyspnea (13), hyporexia or anorexia (13), and muscle wasting (9). Radiographic (n = 39) abnormalities included cardiomegaly (19) and peritoneal (12) and pleural (11) effusion. Common echocardiographic (n = 37) diagnoses included degenerative valve disease (15), dilated cardiomyopathy (7), unclassified cardiomyopathy (4), restrictive cardiomyopathy (3), and hypertrophic cardiomyopathy (2). On ECG (n = 19), supraventricular arrhythmias (16) were more common than ventricular arrhythmias (12). Thirty-five necropsy reports were available, and diagnoses included cardiomyopathy (n = 14), myocarditis (10), and arteriosclerosis (9). Medical management (n = 20) included a wide range of drugs and dosages with few adverse effects. Survival times (n = 36 rabbits) ranged from 1 to 2,353 days with a median cardiac disease-specific survival time of 306 days.

CONCLUSIONS AND CLINICAL RELEVANCE

The findings provided information on the prevalence of cardiovascular disease in rabbits and survival times for affected rabbits. Right-sided, left-sided, and biventricular congestive heart failure occurred equally. Median survival time was lower than that reported for other species. Further research on the diagnosis and treatment of cardiovascular disease in rabbits is needed.

Prediction of clinically important acquired cardiac disease without an echocardiogram in large breed dogs using a combination of clinical, radiographic and electrocardiographic variables

INTRODUCTION

Large breed (LB) dogs develop dilated cardiomyopathy (DCM) and myxomatous mitral valve disease (MMVD). Echocardiography is required for a definitive diagnosis but is not always available. Our objective was to assess the clinical utility of thoracic radiographs alone and in combination with physical examination and electrocardiography findings for the prediction of clinically important DCM or MMVD in LB dogs.

ANIMALS

Four hundred fifty-five client-owned dogs ≥20 kg with concurrent thoracic radiographs and echocardiogram.

MATERIALS AND METHODS

Medical records were reviewed and stored thoracic radiographs and echocardiographic images were measured to classify dogs as normal heart size (NHS), preclinical DCM, clinical DCM, preclinical MMVD (with cardiomegaly), clinical MMVD, or equivocal. Dogs with preclinical MMVD, without cardiomegaly, were classified as NHS. Vertebral heart size (VHS) and vertebral left atrial size (VLAS) were measured. Receiver operating characteristic curves and prediction models were derived.

RESULTS

Prevalence of MMVD (39.3%) was higher than the prevalence of DCM (24.8%), though most MMVD dogs (67.0%) lacked cardiomegaly and were classified as NHS for analysis. The area under the curve for VHS to discriminate between NHS and clinical DCM/MMVD or preclinical DCM/MMVD was 0.861 and 0.712, respectively, while for VLAS, it was 0.891 and 0.722, respectively. Predictive models incorporating physical examination and electrocardiography findings in addition to VHS/VLAS increased area under the curve to 0.978 (NHS vs. clinical DCM/MMVD) and 0.829 (NHS vs. preclinical DCM/MMVD).

CONCLUSIONS

Thoracic radiographs were useful for predicting clinically important DCM or MMVD in LB dogs, with improved discriminatory ability when physical examination abnormalities and arrhythmias were accounted for.

Echocardiographic reference intervals in healthy UK deerhounds and prevalence of preclinical dilated cardiomyopathy: a prospective, longitudinal study

BACKGROUND

Sighthounds have high echocardiographic (ECHO) left ventricular volumes. Establishing robust breed-specific ECHO reference intervals (RI) for screening is important. End-diastolic volume index (EDVI), end-systolic volume index (ESVI) and ejection fraction (EF) reference ranges derived by Simpson's method of discs are not available for deerhounds. The influence of sex or body weight (BW) on left ventricular diameter during diastole (LVDd) and systole (LVDs) has never been reported.

OBJECTIVES

Prospectively determine ECHO RI and assess prevalence of dilated cardiomyopathy (DCM) in healthy UK deerhounds.

ANIMALS

Ninety-nine deerhounds.

METHODS

Deerhounds scored on ECHO and ECG variables then classified as normal (NORM), equivocal (EQUIV) or affected (AFF) with DCM. Fifty-nine NORM deerhounds used to determine ECHO RI.

RESULTS

Prevalence of DCM was 21.6%. There were significant differences in BW (p<0.001), LVDd (p<0.001) and LVDs (p<0.05) between female and male deerhounds. Cut-off values for EDVI (≥140.2 mL/m²: 79% sensitivity/97% specificity), ESVI (≥71.9 mL/m²: 94.7% sensitivity/94.2% specificity) and EF (≤42.1%: 84.2% sensitivity/92.8% specificity) were proposed to help diagnose DCM. The most reliable ECHO variables to identify AFF dogs were LVDs indexed to BW by allometric scaling and ESVI; one of the least reliable was sphericity index. Ventricular arrhythmias (VA) were identified in 13.6% of the population, with the highest prevalence in AFF deerhounds (42%).

CONCLUSIONS

Preclinical DCM in deerhounds is common and VA may be associated with DCM. Healthy deerhounds have higher LVDd, LVDs and EDVI compared with other breeds. This study provides ECHO RIs for deerhounds; sex or BW RIs should be used when screening.

Acute pharmacodynamic effects of pimobendan in client-owned cats with subclinical hypertrophic cardiomyopathy

BACKGROUND

Prior studies have suggested that pimobendan is associated with several positive effects in cats, including improved survival in cats with congestive heart failure and improved left atrial function in research colony cats with hypertrophic cardiomyopathy (HCM) and normal cats. However, there is still a paucity of pharmacodynamic data refuting or supporting the use of pimobendan in a clinical cat population. This clinical trial aimed to evaluate the pharmacodynamic effects and tolerability of a single dose of pimobendan in cats with HCM. Echocardiograms and Doppler-derived systolic blood pressures were performed in 21 client-owned cats with subclinical HCM at baseline and 90-min after oral administration of 1.25 mg of pimobendan (Vetmedin). Seven additional cats were evaluated post-placebo administration to account for intra-day variability.

RESULTS

Heart rate, systolic blood pressure, and murmur grade were not significantly different between baseline and post-pimobendan evaluations. Left auricular blood flow velocity, left atrial size, and left ventricular fractional shortening were not significantly different between baseline and post-pimobendan evaluations. Mean (± standard deviation) tissue Doppler peak systolic velocity of the mitral annulus was significantly higher following pimobendan (7.4 cm/s ± 1.5 vs 8.5 ± 1.6; p = 0.02). Median (min, max) left-ventricular outflow tract maximum velocity was significantly higher following pimobendan [1.9 m/sec (1.5, 3.4) vs 2.6 m/sec (2.0, 4.0); p = 0.01]. Mean right-ventricular outflow tract maximum velocity was also significantly higher following pimobendan (1.5 m/s ± 0.51 vs 2.0 ± 0.53; p = 0.004). Mean left atrial fractional shortening was significantly higher following pimobendan (28% ± 6 vs 32% ± 7; p = 0.02). No adverse events were observed following pimobendan administration. Right ventricular outflow tract velocity was significantly higher following placebo in control cats (1.02 ± 0.21 versus 1.31 ± 0.31; p = 0.01). No other significant differences were detected.

CONCLUSIONS

In client-owned cats with HCM, pimobendan acutely increased left atrial function and mildly increased left ventricular systolic function. Left ventricular outflow tract velocity was increased after pimobendan. Pimobendan was well tolerated in the acute setting in cats with HCM. The findings of this prospective, acute-dosing study confirm previous findings in research animals and retrospective analyses and suggest that chronic dosing studies are safe and warranted.

Diagnosis and management of canine atrial fibrillation

Atrial fibrillation (AF) is the most common non-physiological arrhythmia in dogs and humans. Its high prevalence in both species and the impact it has on survival time and quality of life of affected patients, makes it a very relevant topic for medical research. In dogs, the diagnosis of AF is usually fairly straightforward, but optimal management can be complicated. Rate control is the most commonly used strategy; rhythm control can also be considered in very specific cases. Concurrent congestive heart failure is frequently identified, which represents an extra challenge for the clinicians. This article reviews the current recommendations for the diagnosis and management considerations of AF in dogs. Future perspectives, focusing on new drugs that may prevent development of AF based on recent discoveries, will also be discussed.

Canine atrial fibrillation: Pathophysiology, epidemiology and classification

Atrial fibrillation (AF) is the most common non-physiological arrhythmia in dogs and humans. Its high prevalence in both species and the impact it has on survival time and quality of life of affected patients, makes it a very relevant topic of medical research. Significant developments in understanding the mechanisms underlying this arrhythmia in humans has occurred over the last decades and some of this knowledge is being applied to veterinary medicine, despite the many differences between species. This article reviews the current understanding of the pathophysiology of AF. The epidemiology and classification of AF in dogs will also be discussed.

Echocardiographic and electrocardiographic evaluation of North American Irish Wolfhounds

Background

Cardiac disease is an important cause of morbidity and mortality in Irish Wolfhounds (IWs), but its prevalence and clinical characteristics in North American IWs are incompletely described.

Hypothesis/Objectives

That atrial fibrillation (AF) is a diagnostic marker of echocardiographic abnormalities, and that clinical characteristics predict development of IW cardiomyopathy (IWCM). To define the prevalence of arrhythmias and echocardiographic abnormalities in North American IWs.

Animals

Six hundred and forty‐five adult IWs presented for screening examinations intended to identify familial cardiac disease.

Methods

In this retrospective cohort study, reference intervals defined based on echocardiographic data from IW classified as normal, were used to define the prevalence of structural and functional abnormalities. A logistic model was developed to identify clinical findings that predict future development of IWCM.

Results

The prevalence of AF was 8.9% (95% confidence interval [CI], 6.6‐11.2) of which 55.5% had echocardiographic abnormalities. IWCM defined by left atrial enlargement, left ventricular dilatation, and systolic dysfunction had a prevalence of 1.8% (0.72‐2.8). Positive and negative likelihood ratios for AF in the identification of IWCM were, respectively, 10.8 (7.29‐16) and 0.2 (0.06‐0.69). Multivariable logistic regression identified AF (odds ratio [OR]; 10.6, 95% CI, 2.67‐42.3) and male sex (OR; 3.8, 95% CI, 1.02‐14) as predictors of future development of IWCM.

Conclusions and Clinical Importance

Atrial fibrillation is common in North American IW. It occurs in association with structural cardiac disease but also in its absence. Irish Wolfhounds cardiomyopathy is characterized by chamber enlargement but minimally decreased ejection phase indices of myocardial function. Atrial fibrillation is a risk factor for future development of IWCM.

Irish wolfhounds with subclinical atrial fibrillation: progression of disease and causes of death

INTRODUCTION

To evaluate the frequency of dilated cardiomyopathy (DCM) and cardiac death (CD) in Irish wolfhounds (IW) with subclinical atrial fibrillation (AF) and to compare cardiac and all-cause mortality to those of a contemporaneous control group of apparently healthy IW with sinus rhythm.

ANIMALS

Fifty-two IW with AF, but without echocardiographic evidence of DCM or other cardiac disease, and an age- and gender-matched control cohort of 52 apparently healthy IW.

METHODS

Data from 1552 IW were retrospectively evaluated. Fifty-two dogs with subclinical AF were compared with 52 IW controls. Time from initial diagnosis to development of DCM was recorded, and survival data were analyzed using cumulative incidence functions.

RESULTS

26/52 AF dogs developed DCM. At study end, in the AF and control group each, 49/52 AF dogs had died, three remained alive. Death in the AF cohort was attributed to CD in 22/49 dogs (12 congestive heart failure [CHF], 10 sudden cardiac deaths [SCD]), while 27 dogs died from non-CD. In the control group, significantly fewer dogs developed DCM (11/52 dogs, p=0.004), even fewer died from CD (5/49; three CHF, two SCD; p=0.001). The odd ratios (95% confidence interval) for dogs with AF vs. controls to develop DCM was 3.7 (1.6-8.8) and to die from CD was 7.2 (2.4-21.2). Median all-cause survival for AF IWs (CD, 36.3 months; non-CD, 33.2 months) did not differ significantly from the control group (CD, 28.6 months, p=0.377; non-CD, 45.3 months, p=0.631).

CONCLUSION

IW with subclinical AF commonly develop DCM and die from cardiac death.

Cardiac Therapeutics in Horses

Many cardiac therapeutics lack significant evidence of benefit in the horse, and in many cases their use is based on extrapolation of evidence from other species. In recent years there has been a push to develop a better understanding of both the pharmacodynamics and pharmacokinetics of these drugs. Recent data have described the use of antiarrhythmic agents including sotalol, flecainide, and amiodarone. Data about the use of ACE inhibitors in the management of congestive heart failure are encouraging and support their use in certain cases, wheras evidence for other medicines, such as pimobendan, remain speculative.

Intracoronary Gene Delivery of the Cytoprotective Factor Vascular Endothelial Growth Factor-B167 in Canine Patients with Dilated Cardiomyopathy: A Short-Term Feasibility Study

Dilated cardiomyopathy (DCM) is a myocardial disease of dogs and humans characterized by progressive ventricular dilation and depressed contractility and it is a frequent cause of heart failure. Conventional pharmacological therapy cannot reverse the progression of the disease and, in humans, cardiac transplantation remains the only option during the final stages of heart failure. Cytoprotective gene therapy with vascular endothelial growth factor-B₁₆₇ (VEGF-B₁₆₇) has proved an effective alternative therapy, halting the progression of the disease in experimental studies on dogs. The aim of this work was to test the tolerability and feasibility of intracoronary administration, under fluoroscopic guidance, of VEGF-B₁₆₇ carried by adeno-associated viral vectors in canine DCM patients. Ten patients underwent the gene delivery procedure. The intraoperative phase was well tolerated by all dogs. Clinical and echocardiographic assessments at 7- and 30-days post-procedure showed stable conditions compared to the pre-procedure phase. The results of this work indicate that intracoronary VEGF-B₁₆₇ gene delivery is feasible and tolerated in dogs with DCM. Further monitoring/investigations are ongoing to evaluate the effects of this therapy on disease progression.

Cardiac Effects of a Single Dose of Pimobendan in Cats With Hypertrophic Cardiomyopathy; A Randomized, Placebo-Controlled, Crossover Study

Background: Pimobendan has been shown to impart a significant survival benefit in cardiomyopathic cats who receive it as part of heart failure therapy. However, use of pimobendan remains controversial in cats with hypertrophic cardiomyopathy (HCM) due to lack of pharmacodynamic data for pimobendan in cats with HCM and due to theoretical concerns for exacerbating left ventricular outflow tract obstructions. Hypothesis/Objectives: Our objective was to investigate the cardiac effects of pimobendan in cats with HCM. We hypothesized that pimobendan would not exacerbate left ventricular outflow tract obstructions and that it would improve echocardiographic measures of diastolic function. Animals: Thirteen purpose-bred cats were studied from a research colony with naturally-occurring HCM due to a variant in myosin binding protein C. Methods: Cats underwent two examinations 24 h apart with complete standard echocardiography. On their first day of evaluation, they were randomized to receive oral placebo or 1.25 mg pimobendan 1 h prior to exam. On their second examination, they were crossed over and received the remaining treatment. Investigators were blinded to all treatments. Results: The pimobendan group had a significant increase in left atrial fractional shortening (pimobendan group 41.7% ± 5.9; placebo group 36.1% ± 6.0; p = 0.04). There was no significant difference in left ventricular outflow tract (LVOT) velocities between the groups (pimobendan group 2.8 m/s ± 0.8; placebo group 2.6 m/s ± 1.0). There were no significant differences between the number of cats with LVOT obstructions between groups (12 in pimobendan group; 11 in placebo group; p = 1.00). There were no detectable differences in any systolic measures, including left ventricular fractional shortening, mitral annular plane systolic excursion, and tricuspid annular plane systolic excursion. Doppler-based diastolic function assessment was precluded by persistent tachycardia. Conclusions: Improved left atrial function in the pimobendan group could explain some of the reported survival benefit for HCM cats in CHF. Pimobendan did not exacerbate LVOT obstructions and thus may not be contraindicated in HCM cats with LVOT obstructions. Future studies are needed to better characterize other physiologic effects, particularly regarding diastolic function assessment, and to better assess safety of pimobendan over a longer time-course.

Cardiac Effects of a Single Dose of Pimobendan in Cats With Hypertrophic Cardiomyopathy; A Randomized, Placebo-Controlled, Crossover Study

Background: Pimobendan has been shown to impart a significant survival benefit in cardiomyopathic cats who receive it as part of heart failure therapy. However, use of pimobendan remains controversial in cats with hypertrophic cardiomyopathy (HCM) due to lack of pharmacodynamic data for pimobendan in cats with HCM and due to theoretical concerns for exacerbating left ventricular outflow tract obstructions.

Hypothesis/Objectives: Our objective was to investigate the cardiac effects of pimobendan in cats with HCM. We hypothesized that pimobendan would not exacerbate left ventricular outflow tract obstructions and that it would improve echocardiographic measures of diastolic function.

Animals: Thirteen purpose-bred cats were studied from a research colony with naturally-occurring HCM due to a variant in myosin binding protein C.

Methods: Cats underwent two examinations 24 h apart with complete standard echocardiography. On their first day of evaluation, they were randomized to receive oral placebo or 1.25 mg pimobendan 1 h prior to exam. On their second examination, they were crossed over and received the remaining treatment. Investigators were blinded to all treatments.

Results: The pimobendan group had a significant increase in left atrial fractional shortening (pimobendan group 41.7% ± 5.9; placebo group 36.1% ± 6.0; p = 0.04). There was no significant difference in left ventricular outflow tract (LVOT) velocities between the groups (pimobendan group 2.8 m/s ± 0.8; placebo group 2.6 m/s ± 1.0). There were no significant differences between the number of cats with LVOT obstructions between groups (12 in pimobendan group; 11 in placebo group; p = 1.00). There were no detectable differences in any systolic measures, including left ventricular fractional shortening, mitral annular plane systolic excursion, and tricuspid annular plane systolic excursion. Doppler-based diastolic function assessment was precluded by persistent tachycardia.

Conclusions: Improved left atrial function in the pimobendan group could explain some of the reported survival benefit for HCM cats in CHF. Pimobendan did not exacerbate LVOT obstructions and thus may not be contraindicated in HCM cats with LVOT obstructions. Future studies are needed to better characterize other physiologic effects, particularly regarding diastolic function assessment, and to better assess safety of pimobendan over a longer time-course.

Recurrent bacterial pneumonia in Irish Wolfhounds: Clinical findings and etiological studies

BACKGROUND

Increased incidence of bacterial pneumonia (BP) has been reported in Irish Wolfhounds (IWHs), and recurrence of BP is common. The etiology of recurrent pneumonia in IWHs is largely unknown.

OBJECTIVES

To describe clinical findings in IWHs with recurrent BP and investigate possible etiologies.

ANIMALS

Eleven affected IWHs, 25 healthy IWHs, 28 healthy dogs of other Sighthound breeds, and 16 healthy dogs of other breeds.

METHODS

Prospective cross-sectional observational study. All affected IWHs underwent thorough clinical examinations including thoracic radiographs, thoracic computed tomography, electron microscopic evaluation of ciliary structure, and bronchoscopy and bronchoalveolar lavage fluid (BALF) cytology and culture. Serum and BALF immunoglobulin concentrations were measured using an ELISA method, and peripheral blood lymphocyte subpopulations were analyzed using flow cytometry. Esophageal function was assessed by fluoroscopy (n = 2).

RESULTS

Median age of onset was 5.0 years (range, 0.4-6.5 years), and when presented for study, dogs had experienced a median of 5 previous episodes of BP (range, 2-6). The following predisposing factors to BP were detected: focal bronchiectasis (10/11), unilateral (2/9) and bilateral (1/9) laryngeal paralysis, and esophageal hypomotility (2/2). Local or systemic immunoglobulin deficiencies or primary ciliary defects were not detected.

CONCLUSIONS AND CLINICAL IMPORTANCE

Recurrent BP affects mostly middle-aged and older IWHs without any evident immune deficit or primary ciliary defects. Focal BE was a frequent finding in affected dogs and likely contributed to the development of recurrent respiratory infections. Laryngeal and esophageal dysfunction identified in a minority of dogs may contribute to recurrent BP.

Dilated cardiomyopathy in 151 Irish Wolfhounds: Characteristic clinical findings, life expectancy and causes of death

Dilated cardiomyopathy (DCM) is an important cause of morbidity in Irish Wolfhounds (IW), a breed also predisposed to neoplastic and orthopedic diseases that shorten life expectancy. The objective of this study was to investigate survival and causes of death in IW with DCM and to characterise the clinical findings of DCM over time. Data from cardiovascular examinations performed in 1591 IW, including echocardiography and electrocardiography, were retrospectively evaluated. IW with DCM on medical therapy with long term longitudinal follow-up were included in this study (n=151; 95 males, 56 females). Based on their clinical status at initial diagnosis, IW were classified into one of three groups: preclinical DCM with sinus rhythm (PC-DCM-SR, n=35), preclinical DCM with atrial fibrillation (PC-DCM-AF, n=87), and congestive heart failure with DCM and AF (CHF-DCM-AF, n=29). Survival data were analyzed using cumulative incidence functions, Kaplan-Meier and Cox regression. CHF was predominantly characterized by chylous pleural and mild pericardial effusions. Causes of death were cardiac (CD) in 73/151 and non-cardiac (non-CD) in 62/151; 16 dogs remained alive at study end. The majority of deaths in both preclinical DCM groups were non-CD (PC-DCM-AF=51.9% non-CD, 48.1% CD; PC-DCM-SR, 65.5% non-CD, 34.5% CD). In the CHF-DCM-AF group most dogs (89.6%) experienced a CD. Median survival of the CHF-DCM-AF group (7.3 months) was significantly shorter than in the PC-DCM-AF group (21.9 months) or PC-DCM-SR group (29.1 months, P=0.001). CHF-DCM-AF in IW was associated with reduced life expectancy and CD, while most IW with preclinical DCM died from non-cardiac causes.

Echocardiographic indices of age- and gender-dependent cardiac remodeling over the adult lifespan in Irish Wolfhounds

INTRODUCTION

Characterizing age- and gender-dependent cardiac remodeling over the adult lifespan in Irish Wolfhounds (IWs) by echocardiography. In people, a life-long cardiac remodeling process has been demonstrated.

ANIMALS, MATERIALS, METHODS

Irish Wolfhounds (56 males, 90 females) with no indication of cardiac disease at final assessment (>7.0 years old). For each dog, four transthoracic echocardiographic studies were analyzed. Left ventricular (LV) systolic and diastolic internal dimensions (LVIDs, LVIDd), LV fractional shortening (FS) and ejection fraction (EF), LV free wall and interventricular septal thickness, right ventricular diastolic dimension, and left atrial (LA) and right atrial systolic diameters were compared at time points in the following age categories (years): 1.0-2.5; 3.0-4.0; 4.5-6.0; and 7.0-10.5 and related to age, body weight, and heart rate.

RESULTS

Over the adult life course, males had statistically significant increases in LV internal dimensions, atrial diameters, and decreases of FS and EF. From youngest to oldest age of examination means ± standard deviations were as follows: LVIDs, 32.7 ± 2.9 vs. 36.5 ± 2.9 mm; LVIDd, 49.6 ± 4.7 vs. 53.4 ± 3.8 mm; right atrial diameter, 36.8 ± 3.3 vs. 42.6 ± 3.3 mm; LA, 49.0 ± 3.6 vs. 55.0 ± 3.7 mm; and FS, 34.6 ± 3.7 vs. 31.0 ± 3.2. In females, LV internal dimensions did not change significantly, increases in right atrial (38.1 ± 3.7 mm to 40.0 ± 5.2 mm) and LA diameter (48.8 ± 3.6 to 52.4 ± 4.3 mm) were attenuated, as were decreases of FS (33.4 ± 3.7 to 31.5 ± 4.4, p = 0.02). LV wall thicknesses did not significantly change in both genders.

DISCUSSION AND CONCLUSIONS

Over the adult life course, echocardiography demonstrated increasing LV dimensions in male IWs only. In both genders, FS and EF decreased, and atrial diameters increased. Females showed an attenuated remodeling process.

An update on canine cardiomyopathies - is it all in the genes?

Dilated cardiomyopathy is the second most common cardiac disease in dogs and causes considerable morbidity and mortality. Primary dilated cardiomyopathy is suspected to be familial, and genetic loci have been associated with the disease in a number of breeds. Because it is an adult-onset disease, usually with late onset, testing breeding dogs and bitches before breeding for a genetic mutation that could lead to dilated cardiomyopathy would be helpful to prevent disease. There is growing evidence that the genetic basis may be multigenic rather than monogenic in the majority of studied breeds. This review article describes the known genetic aspects of canine dilated cardiomyopathy and the implications of genetic tests on heart testing and the future of veterinary cardiology.

Retrospective Evaluation of the Effect of Heart Rate on Survival in Dogs with Atrial Fibrillation

Background

Atrial fibrillation (AF) usually is associated with a rapid ventricular rate. The optimal heart rate (HR) during AF is unknown.

Hypothesis/Objectives

Heart rate affects survival in dogs with chronic AF.

Animals

Forty‐six dogs with AF and 24‐hour ambulatory recordings were evaluated.

Methods

Retrospective study. Holter‐derived HR variables were analyzed as follows: mean HR (meanHR, 24‐hour average), minimum HR (minHR, 1‐minute average), maximum HR (maxHR, 1‐minute average). Survival times were recorded from the time of presumed adequate rate control. The primary endpoint was all‐cause mortality. Cox proportional hazards analysis identified variables independently associated with survival; Kaplan‐Meier survival analysis estimated the median survival time of dogs with meanHR <125 bpm versus ≥125 bpm.

Results

All 46 dogs had structural heart disease; 31 of 46 had congestive heart failure (CHF), 44 of 46 received antiarrhythmic drugs. Of 15 dogs with cardiac death, 14 had CHF. Median time to all‐cause death was 524 days (Interquartile range (IQR), 76–1,037 days). MeanHR was 125 bpm (range, 62–203 bpm), minHR was 82 bpm (range, 37–163 bpm), maxHR was 217 bpm (range, 126–307 bpm). These were significantly correlated with all‐cause and cardiac‐related mortality. For every 10 bpm increase in meanHR, the risk of all‐cause mortality increased by 35% (hazard ratio, 1.35; 95% CI, 1.17–1.55; P < 0.001). Median survival time of dogs with meanHR<125 bpm (n = 23) was significantly longer (1,037 days; range, 524‐open) than meanHR ≥125 bpm (n = 23; 105 days; range, 67–267 days; P = 0.0012). Mean HR was independently associated with all‐cause and cardiovascular mortality (P < 0.003).

Conclusions and Clinical Importance

Holter‐derived meanHR affects survival in dogs with AF. Dogs with meanHR <125 bpm lived longer than those with meanHR ≥ 125 bpm.

Occurrence of cardiorespiratory diseases and impact on lifespan in Swedish Irish Wolfhounds: a retrospective questionnaire-based study

BACKGROUND

According to Swedish animal insurance data, Irish Wolfhounds (IW) are 29 times more likely to die from cardiac causes than the baseline breed. Dilated cardiomyopathy (DCM) has a high prevalence in the breed and the disease has been shown to be hereditary in IW. Few studies address respiratory diseases in IW, but reports suggest that the incidence of pneumonia is high. Respiratory diseases are reported as a common cause of death in the breed along with cardiac, neoplastic, musculoskeletal and gastrointestinal diseases. The aim of this study was to investigate mortality, morbidity and lifespan in Swedish IW through a questionnaire-based study. Focus was on DCM and pneumonia and potential association between these diseases. Questionnaires were sent to owners of purebred IW registered in the Swedish Kennel Club, born during 2006-2008. Owners were asked for information concerning occurrence of disease, results of clinical examinations, treatments, cause and date of death.

RESULTS

Overall response rate was 38% (105 completed questionnaires). Median lifespan was 2720 days (7.5 years). Males had shorter lifespan than females (median 2523 and 2836 days, respectively), P = 0.02. The most common causes of death were neoplastic disease (24%), cardiac disease (18%) and respiratory disease (16%). The percentage of dogs with pneumonia on at least one occasion during their lifetime was 37%, with a majority experiencing recurrent episodes (53%). The median lifespan was shorter for dogs affected by pneumonia on at least one occasion (2629 days), compared to dogs without history of pneumonia (2804 days) (P = 0.04), whereas the lifespan did not differ between dogs with or without a diagnosis of DCM. No sex predisposition was found regarding DCM or pneumonia.

CONCLUSIONS

This study showed that DCM and pneumonia are common conditions in IW in Sweden, and that dogs affected by pneumonia have a shorter lifespan than those without history of pneumonia. Considering the results from this study and previous studies regarding these diagnoses in IW; cardiac and respiratory disease should be given further attention in the course of improving the general health of the breed.

Clinical Trials in Veterinary Medicine: A New Era Brings New Challenges

Randomized clinical trials (RCTs) are among the most rigorous ways to determine the causal relationship between an intervention and important clinical outcome. Their use in veterinary medicine has become increasingly common, and as is often the case, with progress comes new challenges. Randomized clinical trials yield important answers, but results from these studies can be unhelpful or even misleading unless the study design and reporting are carried out with care. Herein, we offer some perspective on several emerging challenges associated with RCTs, including use of composite endpoints, the reporting of different forms of risk, analysis in the presence of missing data, and issues of reporting and safety assessment. These topics are explored in the context of previously reported veterinary internal medicine studies as well as through illustrative examples with hypothetical data sets. Moreover, many insights germane to RCTs in veterinary internal medicine can be drawn from the wealth of experience with RCTs in the human medical field. A better understanding of the issues presented here can help improve the design, interpretation, and reporting of veterinary RCTs.

Multiple Genetic Associations with Irish Wolfhound Dilated Cardiomyopathy

Cardiac disease is a leading cause of morbidity and mortality in dogs and humans, with dilated cardiomyopathy being a large contributor to this. The Irish Wolfhound (IWH) is one of the most commonly affected breeds and one of the few breeds with genetic loci associated with the disease. Mutations in more than 50 genes are associated with human dilated cardiomyopathy (DCM), yet very few are also associated with canine DCM. Furthermore, none of the identified canine loci explain many cases of the disease and previous work has indicated that genotypes at multiple loci may act together to influence disease development. In this study, loci previously associated with DCM in IWH were tested for associations in a new cohort both individually and in combination. We have identified loci significantly associated with the disease individually, but no genotypes individually or in pairs conferred a significantly greater risk of developing DCM than the population risk. However combining three loci together did result in the identification of a genotype which conferred a greater risk of disease than the overall population risk. This study suggests multiple rather than individual genetic factors, cooperating to influence DCM risk in IWH.