Introduction
Other than heartworm disease, the most important cardiovascular syndrome in veterinary medicine is canine chronic mitral valvular disease (canine chronic valvular heart disease - CCVHD, endocardiosis, myxomatous valve degeneration, mitral regurgitation [MR]), affecting 85% of dogs aged 13 years or older and constituting 75% of canine heart disease.1
The American College of Veterinary Internal Medicine's Board of Regents selected a group of European and U.S. ACVIM-boarded cardiologists to arrive at a consensus as to the diagnosis and treatment of CCVHD.1 Appropriately, the 10 panel members represented diverse points of view on cardiac therapeutics. Evidence was derived from sources ranging from placebo-controlled, double-blind clinical trials and other experimental data to anecdote, clinical experience, and expert opinion, with greater weight put on the former. To achieve consensus, all 10 panelists had to agree on the recommendation. In addition to putting forth consensus recommendations on diagnostic and therapeutic options, the panel revealed instances when the majority of panelists agreed upon a recommendation, even if consensus was not reached. The group chose to use a new grading system for cardiac disease severity and progression, which is described below. In addition to the panels' recommendations, the authors will render their own personal opinion, when it is appropriate to do so (CA will comment on medical aspects and LF will comment on nutritional aspects of treatment). Space constraints preclude discussion of the panel's recommendations on diagnostic steps for each category of CCVHD and treatment recommendations for refractory heart failure (Stage D). Hence we will cover only management recommendations for dogs at risk for CCVHD, those with very early disease, those with cardiac enlargement, those hospitalized for heart failure, and those treated for heart failure at home.
The Consensus panel did not have a nutritionist or nutritionist's input. In this presentation and manuscript, we will meld the medical and nutritional aspects of managing cardiac disease for each stage of heart disease, as defined by the ACVIM Consensus Panel on Mitral Valve Disease. It should be noted that the nutritional recommendations below are those of one of the authors (LF) and not of the ACVIM Consensus panel.
Mitral Valve Disease Severity Classification
The panel chose to adapt a novel classification scheme modeled after that put forth by the American Heart Association and the American College of Cardiology. This scheme avoids the NYHA classification pitfall of using progressive loss of exercise tolerance to grade disease severity. In addition, it adds an early category (A), during which dogs are without evidence of disease, but are at risk for developing disease (e.g., Cavalier King Charles Spaniels). The ACVIM classification system is shown in Figure 1. Class A CCVHD patients are at risk, B1 have murmurs but no cardiomegaly, B2 have cardiomegaly, Ca have acute heart failure, requiring hospitalization, Cc have chronic heart failure and are treated at home, Da patients have refractory heart failure, requiring hospitalization, while Dc have refractory heart failure but can be managed at home. The panel attempted to achieve consensus on the management of dogs in all categories of severity. Only the therapeutic recommendations for ACVIM Class A through C are discussed herein.
Stage A CCVHD
Consensus
The panel recommends no drug therapy during this stage. Breeding stock in which a murmur of mitral regurgitation is discovered during the normal breeding years (6–8 years) should be removed from the breeding program.
Nutrition
There currently is no evidence that dietary changes in Stage A can reduce the risk for CCVHD.
There are, however, general nutrition guidelines that can help to maintain health in dogs:
Perform a nutritional assessment at each visit. This includes a complete diet history and assessment of body weight, body condition score (BCS), and muscle condition score (MCS). See the WSAVA Nutrition Toolkit for tools to assess each of these important components of nutritional health.
If you identify any concerns from the diet history (e.g., unbalanced home-cooked diet, vegetarian or raw diets, inappropriate dietary supplements, suboptimal BCS [< 4 or > 5], or muscle loss), additional investigation is warranted.
Make specific nutritional recommendations, even if this is just to tell the owner that he/she is feeding the right food in the correct amount. If the diet is not optimal (e.g., too many treats, unconventional diet, < 4/9 or > 5/9 BCS), make specific recommendations for a more appropriate food or an adjusted amount of food.
Ensure dogs are eating a good quality, nutritionally complete and balanced dog food made by a well-known, reputable manufacturer. For recommendations on selecting a good quality pet food, see the WSAVA Nutrition Toolkit.
Stage B1 CCVHD
Consensus
No drug or dietary therapy is recommended for either small or large dogs with MR.
Nutrition
General: Perform a nutritional assessment at each visit and make specific dietary recommendations.
Sodium: The author aims for a dog food with a sodium content of < 100 mg/100 kcal. This is also an opportune time to begin talking to the owner about the animal's overall dietary patterns (e.g., the dog's food, treats, table food, rawhides, dental products, and methods of administering medications), since it is generally much easier to institute dietary modifications when the animal is asymptomatic.
Body composition: Body condition score = 4–5/9 and avoid muscle loss
Stage B2 CCVHD
Consensus
None (The panel was not unanimous on any recommendation at this state.)
Majority
ACE-inhibitors were recommended by the majority of panelists for dogs with CCVHD and cardiac remodeling (enlargement). A majority of panelists recommended against the use of beta-blockers at this disease stage. A majority of panelists suggested dietary alteration, including mild salt restriction, high palatability and adequate protein and carbohydrate content.
Author's Comment
Although controversial,2 the author does utilize ACE-inhibitors in Stage B2 CCVHD, as the majority of evidence supports their use.3,4 In an unpublished survey of 100 ACVIM-boarded cardiologists, nearly 60% used ACE-inhibitors in small breeds and nearly 70% in large breeds, at this stage of CCVHD.5 For more dedicated clients, we have employed up-titration of a beta-blocker (e.g., carvedilol or atenolol), but now are more likely to consider the use of spironolactone, based on recent evidence from our laboratory indicating that "aldosterone breakthrough" occurs with ACE-inhibitors in normal dogs undergoing furosemide-induced RAAS activation. This indicates that, for "complete" renin-angiotensin-aldosterone (RAAS) suppression, drugs which blunt this system at different points in the cascade are possibly indicated.6 Specific data from clinical trials, for the moment, are lacking for both beta- and aldosterone-receptor blockade in Stage B2 CCVHD.
Nutrition
General: Perform a nutritional assessment at each visit and make specific dietary recommendations.
Sodium: The author aims for a dog food with a sodium content of < 100 mg/100 kcal. Be sure to discuss appropriate dog foods, treats, table food, rawhides, dental products, and methods of administering medications to ensure the entire diet is optimized.
Body composition: Body condition score = 5–6/9 and avoid muscle loss
Protein: Ensure adequate protein intake (at least 5.1 gm/100 kcal) unless concurrent severe chronic kidney disease is present.
Other nutritional recommendations: One small study compared a moderately reduced-sodium cardiac diet that was enriched with omega-3 fatty acids, antioxidants, arginine, taurine, and carnitine with a placebo diet in dogs with stage B1 and B2 CCVHD (Freeman et al. 2006). The group fed the cardiac diet had increased circulating concentrations of key nutrients (e.g., antioxidants, omega-3 fatty acids) and reduction in cardiac size. This change in cardiac size did not appear to be an effect of sodium restriction. However, the effect of dietary modifications on progression of disease is unknown. In addition, one retrospective study showed a significantly longer survival time in dogs with cardiac disease that were receiving omega-3 fatty acid supplementation (Slupe et al. 2008). Although much additional research is needed, the author recommends fish oil supplementation (40 mg/kg eicosapentaenoic acid [EPA] and 25 mg/kg docosahexaenoic acid [DHA]) if the taste is acceptable to the dog or if the dog can be pilled.
Stage C - Hospitalized/Acute (CA) CCVHD
Consensus
A consensus was reached by the panel on the use of furosemide (PO, IM, IV, CRI7,8) and pimobendan for hospitalized heart failure patients. As clinical conditions dictate, the panel also agreed that oxygen, using cage or nasal tube; mechanical fluid removal (thoracic or abdominal fluid which contributes to dyspnea); specific nursing measures to relieve dyspnea/discomfort (appropriate humidity and temperature and body positioning); sedation (e.g., buprenorphine and/or acepromazine; morphine); and nitroprusside (mixed vasodilator) and/or dobutamine (inotropic effect, afterload reduction, mitral orifice size reduction) by CRI.
Majority
Although consensus was not reached, a majority of panelists recommended ACE-inhibitors as off-loading (vasodilators) in the acute Stage C patient. This approach is supported by human studies evaluating IV enalaprilat (the active metabolite of enalapril) in acute heart failure9,10 and the results of the IMPROVE Trial which demonstrated a fall in pulmonary artery wedge pressure (equivalent to left atrial pressure, the driving pressure producing pulmonary edema) with oral enalapril therapy.11
Author's Comment
Only a minority of panelists advocate the use of nitroglycerin in these patients. Our view is that this additional off-loading therapy is beneficial and is used in place of the somewhat cumbersome nitroprusside. Our standard approach to the hospitalized Stage C patient includes administration furosemide (IV or IM bolus or CRI), enalapril, and pimobendan, with oxygen (in most), dobutamine, digoxin (if in atrial fibrillation) and nitroglycerine added as patient needs dictate.
Nutrition
General: Perform a nutritional assessment. Try to avoid making any major dietary changes in a dog with hospitalized heart failure patients unless the usual diet is extremely high in sodium. Changes during this time can cause food aversions. It usually is preferable to wait until the dog is stabilized (CcCCVHD) before instituting major dietary changes.
Stage C - Outpatient/Chronic (Cc ) CCVHD
Consensus
Consensus was reached by the panel on the use of oral furosemide, an ACE-inhibitor11-16, and pimobendan17 ("triple therapy") for Stage C patients after release from the hospital. The panel also unanimously recommends that beta-blockers not be instituted in Stage C dogs exhibiting signs of heart failure.
Majority
The majority of panelists recommended the use of the aldosterone receptor blocker, spironolactone, for chronic Stage C patients. Likewise, the majority of panelists advocated the use of twice daily enalapril if this is the ACE-inhibitor being used or an equivalent dosage of another agent. In the face of atrial fibrillation, the majority of panelists advocate the use of digoxin to support cardiac function and to slow the ventricular response to atrial fibrillation.
Author's Comment
It is noteworthy that the Consensus Report was prepared prior to the publication of a placebo-controlled, double-blind study demonstrating the positive impact achieved with the addition of spironolactone to standard therapy in dogs in heart failure.18 While it cannot be said with certainty, the panel may well have reached consensus on the use of spironolactone in Stage C dogs had this information been available during the panel's deliberations. As mentioned above, the argument for adding spironolactone is strengthened by the study from one of the authors' laboratories (CA) demonstrating early "aldosterone breakthrough" with ACE-inhibition in a model of heart failure therapy, indicating that an ACE-inhibitor alone may not adequately suppress the circulating RAAS.6
CCVHD, if of sufficient severity, is in actuality a "surgical" disease. To date, unfortunately, efforts at valve repair or replacement have not been met with adequate success. Recently published case series of surgical mitral valve repair have provided disappointing results with high perioperative mortality with valve repair19 and postoperative thrombus formation with valve replacement,20 although some individual successes have been achieved. These results are certainly due, in part, to the fact that surgical correction is delayed until heart failure has ensued. Nevertheless, because of the cost, small numbers of participating centers and limited success, surgical correction of CCVHD is not currently practical, leaving this as a "medically managed disease" in veterinary patients for the time being.
Consensus statements by their very nature represent a compromise of positions, regardless of the subject under discussion. The ACVIM Consensus Statement on Canine Chronic Valvular Heart Disease is no different. The very act of compromising creates a safer, less daring approach to cardiac therapeutics that most can agree upon. It takes out of the mix the more aggressive, less well-proven approaches that might be part of the next consensus statement, but reduces the risks associated with partaking in such practices. It should be noted that this paper reviews only a portion of the consensus statement, and the author recommends that the whole document be read for the recommendations on diagnosis in CCVHD for subtle nuances in treatment approaches, drug dosages, and recommendations for diagnosis and management of refractory heart failure.
Nutrition
General: Perform a nutritional assessment at each visit and make specific dietary recommendations.
Sodium: The author aims for a dog food with a sodium content of < 80 mg/100 kcal. Be sure to discuss appropriate dog foods, treats, table food, rawhides, dental products, and methods of administering medications to ensure the entire diet is optimized.
Body composition: Body condition score = 5–7/9 and minimize muscle loss
Protein: Ensure adequate protein intake (at least 5.1 gm/100 kcal; more if any muscle loss is present) unless concurrent severe chronic kidney disease is present.
Other nutritional recommendations:
Omega-3 fatty acids: Although much additional research is needed, the author recommends fish oil supplementation (40 mg/kg eicosapentaenoic acid [EPA] and 25 mg/kg docosahexaenoic acid [DHA]) if the taste is acceptable to the dog or the dog can be pilled.
Potassium: Monitor for hyperkalemia (especially if using potassium-sparing diuretics or ACE inhibitors) and hypokalemia (especially if using high doses of diuretics).
Magnesium: Monitor for hypomagnesemia (especially if using high doses of diuretics).
Discuss appetite issues with the owner: Once CHF arises, alterations in appetite are common. These can include a complete loss of appetite (anorexia), a reduction in food intake (hyporexia), or changes in food preferences (dysrexia). These all contribute to reduced food intake and resulting weight and muscle loss, which are common in heart failure. These changes in appetite can be caused by increased production of inflammatory mediators (e.g., inflammatory cytokines, or oxidative stress), side effects of cardiac medications, or poor control of heart failure.
Abbreviations
ACE - Angiotensin Converting Enzyme
ACVIM - American College of Veterinary Internal Medicine
CCVD - Canine Chronic Valvular Disease
CRI - Continuous Rate Infusion
IM - Intramuscular
ISACHC - International Small Animal Cardiac Health Council
IV - Intravenous
MR - Mitral Regurgitation
NYHA - New York Heart Association
RAAS - Renin-Angiotensin-Aldosterone System
| Figure 1. The American College of Veterinary Internal Medicine (ACVIM) classification of cardiac disease (from Atkins CE, Haggstrom J. Medical management of mitral valve disease. J Vet Cardiol. 2009). | 
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References
1. Tufts Cummings School of Veterinary Medicine. HeartSmart: Information on pets with heart disease. www.tufts.edu/vet/heartsmart.
2. World Small Animal Veterinary Association Global Nutrition Committee. WSAVA Nutrition Toolkit Website: www.wsava.org/nutrition-toolkit (body and muscle condition score charts, feeding guidelines, effective internet use for owners, diet history forms, calorie requirements for dogs and cats, recommendations for selecting a pet food, etc.).