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An Urban Experience
Chronic therapy
Dogs with CHF may present with clinical signs mild enough to allow home therapy, or they may have been previously stabilized during hospitalization for acute
CHF. Again, DCM dogs are more likely to present with an arrhythmia that might need controlling. Most clinical studies in veterinary cardiovascular medicine are aimed at investigating pharmacological effects and outcomes in this disease category.
The ACVIM panelists recommended the following agents for home therapy (so-called “triple therapy”) for class C dogs by consensus:
• Furosemide(1–2mg/kgPOq12hto4–6mg/kgPOq8h)
• Pimobendan (0.25–0.3 mg/kg q12h)
• ACE-inhibitortherapy(e.g.,enalapril0.5mg/kg,POq12h)
Other drugs that may be considered:
• Spironolactone (0.25–2.0 mg/kg PO q12–24h)
• Digoxin
• Beta-adrenergic receptor antagonists
• Cough suppressants
• Bronchodilators
Clinical trials in MMVD class C dogs
To study the effect of pimobendan on survival in dogs with CHF secondary to MMVD, the QUEST study was untaken. The aim of the study was to compare the time taken to reach the primary endpoint for dogs receiving either pimobendan or benazepril in conjunction with other therapy. The primary endpoint was a composite of spontaneous cardiac death/euthanasia or treatment failure. 260 dogs were recruited and dogs were included if they had demonstrated evidence of CHF. Dogs receiving pimobendan had a longer survival time compared to those receiving benazepril (pimobendan 267 days versus. benazepril 140 days, P=0.0099),
a difference in survival time that is of genuine clinical importance.
The introduction of the ACE-inhibitors to the veterinary market in the early 1990’s and the clinical trials, upon which market approval was based, represented a landmark in the advancement of evidence based veterinary medicine. These studies show that ACE- inhibitor are indicated in advanced MMVD with CHF, as adjunct therapy to diuretics, because dogs receiving
an ACE-inhibitor benefitted in terms of time until death, euthanesia or treatment failure, when compared to ACE- inhibitor dogs.
Spironolactone is approved for use within the European Union in dogs with CHF, secondary to MMVD, as adjunctive therapy at a dosage of 2 mg/kg q 24h. This approval was based on improved survival in double-blind,
placebo-controlled trials in dogs receiving spironolactone and standard therapy as compared to the placebo group.
Clinical trials in DCM class C
Chronic home therapy of dogs with DCM is similar to that of dogs with MMVD. In comparison to placebo, pimobendan has been shown to prolong survival times in Doberman Pinschers with DCM, and ACE-inhibitors have been shown to improve quality of life variables in two large clinical studies.
Refractory heart failure (Class D)
Class D denotes dogs which have developed signs of CHF and/or low output signs (e.g., exercise intolerance, weakness, syncope) and which have been treated and relapsed or failed to respond to standard CHF therapy consisting of recommended drugs and dosages. Dogs in class D are more likely in need of body cavity centesis than in other classes. Very limited numbers of clinical studies are available for dogs in refractory heart failure. This stage represents advanced stages of the disease, and measures instituted may only serve to buy limited extra time. Accordingly, owners should be educated of the prognosis.
Concluding Comments
While there are many unanswered questions in the management of CHF in dogs, clearly progress has been made in our understanding as to which pharmacological agents may be useful; how we might use them; and
in which particular circumstances they will be most valuable. Perhaps even more importantly, we have observed a shift in the demand for data to support our clinical decisions, by both academic and private practitioners and by the public as well. There are, however, areas that need further studies, particularly optimal management of acute CHF.
Selected References
Atkins C, Bonagura J, Ettinger S, et al. Guidelines for the diagnosis and treatment of canine chronic valvular heart disease. J Vet Intern Med 2009;23:1142-1150.
Ettinger SJ, Benitz AM, Ericsson GF, et al. Effects of enalapril maleate on survival of dogs with naturally acquired heart failure. The Long-Term Investigation of Veterinary Enalapril (LIVE) Study Group. J Am Vet Med Assoc 1998;213:1573- 1577.
Kvart C, Häggström J, Pedersen HD, et al. Efficacy of enalapril for prevention of congestive heart failure in dogs with myxomatous valve disease and asymptomatic mitral regurgitation. J Vet Intern Med 2002;16:80-88.
Häggström J, Boswood A, O’Grady M, et al. Effect of Pimobendan or Benazepril Hydrochloride on Survival Times in Dogs with Congestive Heart Failure Caused by Naturally Occurring Myxomatous Mitral Valve Disease: The QUEST Study. J Vet Intern Med 2008;22:1124-1135.
Summerfield NJ, Boswood A, O’Grady MR, et al. Efficacy of pimobendan in the prevention of congestive heart failure or sudden death in Doberman Pinschers with preclinical dilated cardiomyopathy (the PROTECT Study). J Vet Intern Med 2012;26:1337-1349.
Boswood A, Häggström J, Gordon SG, et al. Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study-A Randomized Clinical Trial. J Vet Intern Med 2016;30:1765-1779.

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