Effect of torsemide and furosemide on clinical, laboratory, radiographic and quality of life variables in dogs with heart failure secondary to mitral valve disease.

OBJECTIVES: Diuretic therapy reduces preload and relieves congestion secondary to cardiac dysfunction. Torsemide (torasemide) is a loop diuretic with longer duration of action, decreased susceptibility to diuretic resistance, and adjunctive aldosterone antagonist properties compared with furosemide. We hypothesized that torsemide would be well tolerated and no less effective than furosemide at diuresis, control of clinical signs, and maintenance of quality of life (QOL) in dogs with congestive heart failure (CHF). ANIMALS, MATERIALS AND METHODS: Seven client-owned dogs with stable CHF receiving twice daily oral furosemide and adjunctive medications. Utilizing a double-blinded, randomized, crossover design, dogs were administered either oral furosemide at their current dose or an equivalent oral dose of torsemide (1/10 of the daily furosemide dose divided into twice daily dosing) on day 0. Crossover occurred at day 7 and the study ended on day 14. Clinical, laboratory, radiographic, and QOL variables were evaluated on days 0, 7 and 14. RESULTS: No dogs developed recurrent CHF during the study. Mean furosemide dose on day 0 was 5.13 mg/kg/day (range 2.8-9.6). Following torsemide treatment, creatinine (P = 0.020), urea nitrogen (P = 0.013), phosphorus (P = 0.032), albumin (P = 0.019), carbon dioxide (P = 0.015) and anion gap (P = 0.005) were significantly increased, and urine specific gravity (P = 0.004) and chloride (P = 0.021) were significantly decreased compared with furosemide dosing. No differences in QOL were found. CONCLUSIONS: Results indicate that torsemide is equivalent to furosemide at controlling clinical signs of CHF in dogs and is likely to achieve greater diuresis vs. furosemide. Larger clinical trials evaluating torsemide as a first or second-line loop diuretic for congestive heart failure in dogs are warranted.

Long-term restoration of cardiac dystrophin expression in golden retriever muscular dystrophy following rAAV6-mediated exon skipping.

Although restoration of dystrophin expression via exon skipping in both cardiac and skeletal muscle has been successfully demonstrated in the mdx mouse, restoration of cardiac dystrophin expression in large animal models of Duchenne muscular dystrophy (DMD) has proven to be a challenge. In large animals, investigators have focused on using intravenous injection of antisense oligonucleotides (AO) to mediate exon skipping. In this study, we sought to optimize restoration of cardiac dystrophin expression in the golden retriever muscular dystrophy (GRMD) model using percutaneous transendocardial delivery of recombinant AAV6 (rAAV6) to deliver a modified U7 small nuclear RNA (snRNA) carrying antisense sequence to target the exon splicing enhancers of exons 6 and 8 and correct the disrupted reading frame. We demonstrate restoration of cardiac dystrophin expression at 13 months confirmed by reverse transcription-PCR (RT-PCR) and immunoblot as well as membrane localization by immunohistochemistry. This was accompanied by improved cardiac function as assessed by cardiac magnetic resonance imaging (MRI). Percutaneous transendocardial delivery of rAAV6 expressing a modified U7 exon skipping construct is a safe, effective method for restoration of dystrophin expression and improvement of cardiac function in the GRMD canine and may be easily translatable to human DMD patients.

Use of the loop diuretic torsemide in three dogs with advanced heart failure.

Diuretics are a mainstay of therapy in dogs with heart failure. In dogs with advanced heart failure, moderate to high doses of loop diuretics such as furosemide are used with diminishing effects as profound activation of neuroendocrine systems promote signs of congestive heart failure. The loop diuretic torsemide has several characteristics that make it suitable for treatment of advanced heart failure including longer half-life, increased potency of diuretic action, and anti-aldosterone effects. This case report details the administration of torsemide in 3 dogs with advanced heart failure and apparent furosemide resistance.

Long-term systemic myostatin inhibition via liver-targeted gene transfer in golden retriever muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a lethal, X-linked recessive disease affecting 1 in 3,500 newborn boys for which there is no effective treatment or cure. One novel strategy that has therapeutic potential for DMD is inhibition of myostatin, a negative regulator of skeletal muscle mass that may also promote fibrosis. Therefore, our goal in this study was to evaluate systemic myostatin inhibition in the golden retriever model of DMD (GRMD). GRMD canines underwent liver-directed gene transfer of a self-complementary adeno-associated virus type 8 vector designed to express a secreted dominant-negative myostatin peptide (n = 4) and were compared with age-matched, untreated GRMD controls (n = 3). Dogs were followed with serial magnetic resonance imaging (MRI) for 13 months to assess cross-sectional area and volume of skeletal muscle, then euthanized so that tissue could be harvested for morphological and histological analysis. We found that systemic myostatin inhibition resulted in increased muscle mass in GRMD dogs as assessed by MRI and confirmed at tissue harvest. We also found that hypertrophy of type IIA fibers was largely responsible for the increased muscle mass and that reductions in serum creatine kinase and muscle fibrosis were associated with long-term myostatin inhibition in GRMD. This is the first report describing the effects of long-term, systemic myostatin inhibition in a large-animal model of DMD, and we believe that the simple and effective nature of our liver-directed gene-transfer strategy makes it an ideal candidate for evaluation as a novel therapeutic approach for DMD patients.

Cardiac gene transfer of short hairpin RNA directed against phospholamban effectively knocks down gene expression but causes cellular toxicity in canines.

Derangements in calcium cycling have been described in failing hearts, and preclinical studies have suggested that therapies aimed at correcting this defect can lead to improvements in cardiac function and survival. One strategy to improve calcium cycling would be to inhibit phospholamban (PLB), the negative regulator of SERCA2a that is upregulated in failing hearts. The goal of this study was to evaluate the safety and efficacy of using adeno-associated virus (AAV)-mediated cardiac gene transfer of short hairpin RNA (shRNA) to knock down expression of PLB. Six dogs were treated with self-complementary AAV serotype 6 (scAAV6) expressing shRNA against PLB. Three control dogs were treated with empty AAV6 capsid, and two control dogs were treated with scAAV6 expressing dominant negative PLB. Vector was delivered via a percutaneously inserted cardiac injection catheter. PLB mRNA and protein expression were analyzed in three of six shRNA dogs between days 16 and 26. The other three shRNA dogs and five control dogs were monitored long-term to assess cardiac safety. PLB mRNA was reduced 16-fold, and PLB protein was reduced 5-fold, with treatment. Serum troponin elevation and depressed cardiac function were observed in the shRNA group only at 4 weeks. An enzyme-linked immunospot assay failed to detect any T cells reactive to AAV6 capsid in peripheral blood mononuclear cells, heart, or spleen. Microarray analysis revealed alterations in cardiac expression of several microRNAs with shRNA treatment. AAV6-mediated cardiac gene transfer of shRNA effectively knocks down PLB expression but is associated with severe cardiac toxicity. Toxicity may result from dysregulation of endogenous microRNA pathways.

Cardiac troponin-I concentrations in dogs with bradyarrhythmias before and after artificial pacing.

OBJECTIVES: To quantify cardiac troponin-I (cTnI) concentration in dogs with symptomatic bradyarrhythmias before and after artificial pacing and to correlate cTnI concentration with diagnosis, echocardiographic parameters, serology, and outcome. ANIMALS, MATERIALS AND METHODS: Medical records from the University of Pennsylvania from 2006 to 2009 were reviewed, and 14 dogs with cTnI assay results before and after pacemaker were identified. The ECG diagnosis included complete atrioventricular block (AVB), sick sinus syndrome, 2nd degree AVB, and atrial standstill. Serology, presence of premature beats, echocardiographic measurements, and pacing modality were recorded. RESULTS: Mean cTnI concentration was elevated both pre- and post-pacing, and was significantly higher pre-pacing vs. post-pacing. Post-pacing cTnI concentration in 9 of 14 dogs (64%) remained above the reference range. Four dogs yielded high serum titers for Bartonella spp. Four dogs with markedly increased cTnI concentration had progressive left ventricular enlargement and myocardial failure as compared to pre-pacing examination. CONCLUSIONS: Elevated cTnI concentration suggests that cardiac injury persists after artificial pacing in dogs with bradyarrhythmias. Myocarditis secondary to Bartonella spp. or other causes may be an important cause of AVB in dogs. Prospective studies investigating the correlation of cTnI to potential etiology and development of post-pacing LV dysfunction and outcome are needed.

Cardiac troponin I concentrations following medetomidine-butorphanol sedation in dogs.

OBJECTIVE: To evaluate the effect of medetomidine-butorphanol sedation on serum cardiac troponin I (cTnI) concentration, a marker of myocardial ischemia and injury, in healthy dogs undergoing pre-surgical radiographs for orthopedic procedures. STUDY DESIGN: Prospective clinical study. ANIMALS: Twenty client-owned dogs with no history of cardiac disease. METHODS: Dogs were evaluated for pre-existing cardiac disease with electrocardiogram (ECG), noninvasive blood pressure and echocardiogram. Sedation was achieved using a combination of medetomidine (10 microg kg(-1)) and butorphanol (0.2 mg kg(-1)) intravenously. Blood pressure, heart rate and ECG were serially recorded throughout the duration of sedation. Serum cTnI concentration was measured at baseline and 6, 18, and 24-hours post-sedation. RESULTS: Following administration of medetomidine and butorphanol, all dogs were adequately sedated for radiographs and had a decreased heart rate and increased diastolic blood pressure. Arrhythmias associated with increased parasympathetic tone occurred, including a sinus arrhythmia further characterized as a sinus bigeminy in 17 of the dogs. Serum cTnI was undetectable at all time points in all but three dogs. Two of the three dogs had a detectable concentration of cTnI at all time points measured, including prior to sedation. Only one of the two dogs had a cTnI concentration above the normal reference interval. The dogs that exhibited detectable cTnI had no significant difference in signalment, heart rate, blood pressure, or lactate concentration as compared to those with undetectable cTnI. CONCLUSIONS AND CLINICAL RELEVANCE: Sedation with medetomidine and butorphanol had predictable cardiovascular effects including bradycardia, an increase in arterial blood pressure, and arrhythmias in apparently healthy dogs requiring radiographs for orthopedic injuries, but did not induce significant increases in serum cTnI concentration following the drug doses used in this study.

The use of NT-proBNP assay in the management of canine patients with heart disease.

The diagnosis and management of canine heart disease could be facilitated by a highly sensitive and specific laboratory test that predicts risk of morbidity and mortality, is helpful in directing therapy, easy to perform, inexpensive, and widely available. This article details if, how, and when the cardiac biomarker, N-terminal fragment of the prohormone B-type natriuretic peptide (NT-proBNP), helps in the diagnosis and management of canine heart disease. Veterinary cardiac biomarkers, specifically NT-proBNP, hold great promise. The incorporation of NT-proBNP assay into successful clinical practice requires an understanding of the science behind the technology, as well as the clinical data available to date.