Abstract

This is the report of the American College of Veterinary Internal Medicine (ACVIM) Specialty of Cardiology consensus panel convened to formulate guidelines for the diagnosis and treatment of chronic valvular heart disease (CVHD, also known as endocardiosis and myxomatous valve degeneration) in dogs. It is estimated that approximately 10% of dogs presented to primary care veterinary practices have heart disease, and CVHD is the most common heart disease of dogs in many parts of the world, accounting for approximately 75% of canine cases of heart disease cases seen by veterinary practices in North America. CVHD most commonly affects the left atrioventricular or mitral valve, although in approximately 30% of cases the right atrioventricular (tricuspid) valve also is involved. The disease is approximately 1.5 times more common in males than in females. Its prevalence is also higher in smaller (7.5% of the patient's normal, predisease weight, not including weight loss associated with the resolution of edema or the removal of body cavity effusions. Cachexia has substantial negative prognostic implications, and is much easier to prevent that to treat.32 Consensus recommendations: Maintain adequate calorie intake (maintenance calorie intake in Stage C should provide approximately 60 kcal/kg body weight) to minimize weight loss (specifically muscle mass loss) that often occurs in CHF. Specifically address and inquire about the occurrence of anorexia, and make efforts to treat any drug-induced or other identifiable causes of anorexia that occur. Record the accurate weight of the patient at every clinic visit, and investigate the cause of weight gain or loss. Ensure adequate protein intake and avoid low-protein diets designed to treat chronic kidney disease, unless severe concurrent renal failure is present. Modestly restrict sodium intake, taking into consideration sodium from all dietary sources (including dog food, treats, table food, and foods used to administer medications) and avoid any processed or other salted foods. Monitor serum potassium concentrations and supplement the diet with potassium from either natural or commercial sources if hypokalemia is identified. Hyperkalemia is relatively rare in patients treated for heart failure with diuretics, even in those concurrently receiving an ACEI in combination with spironolactone.33 Diets and foods with high potassium content should be avoided when hyperkalemia has been identified. No consensus was reached on the following dietary therapy for Stage C: Consider monitoring serum magnesium concentrations, especially as CHF progresses and in animals with arrhythmias. Supplement with magnesium in cases in which hypomagnesemia is identified. Consider supplementing with n-3 fatty acids, especially in dogs with decreased appetite, muscle mass loss, or arrhythmia.34 Stage D—Patients have clinical signs of failure refractory to standard treatment for Stage C heart failure from CVHD, as outlined above. Stage D heart failure patients therefore should be receiving the maximal recommended (or tolerated) dosage of furosemide, an ACEI, and pimobendan, as outlined in the Stage C guidelines above. Any indicated and tolerated antiarrhythmic medication, needed to maintain sinus rhythm (if possible) or regulate the ventricular response to atrial fibrillation in a heart rate range of 80–160/min, also should be used before a patient is considered refractory to standard therapy. Not surprisingly, there have been very few clinical trials addressing drug efficacy and safety in this patient population. This leaves cardiologists treating patients with heart failure refractory to conventional medical therapy with a perplexing variety of treatment options. Because of the relative lack of clinical trial evidence and the diverse clinical presentations of patients with end-stage heart failure, development of meaningful consensus guidelines regarding the timing and implementation of individual pharmacologic and dietary treatment strategies for Stage D patients proved difficult. As with Stage C, guidelines for drug treatment are provided for both in-hospital (acute) and for home care (chronic) management of heart failure, and recommendations for chronic dietary therapy are also given. Because Stage D heart failure patients are, by definition, refractory to the treatments for Stage C patients, defining refractory congestive heart failure involves the same diagnostic steps outlined for Stage C plus the finding of failure to respond to treatments outlined in the Stage C guidelines. Consensus recommendations: In the absence of severe renal insufficiency (ie, serum creatinine concentrations > 3 mg/dL), additional furosemide is administered IV as a bolus at a dosage of 2 mg/kg followed by either additional bolus doses, or a furosemide CRI at a dosage of 1 mg/kg/h until respiratory distress (rate and effort) has decreased, or for a maximum of 4 hours. As indicated above, the dosage or furosemide is a range and higher or lower doses may be appropriate for a given case. Continue to allow patient free access to water once diuresis has begun. Fluid removal (eg, abdominal paracentesis, thoracocentesis) as needed to relieve respiratory distress or discomfort. In addition to oxygen supplementation as in Stage C (above), mechanical ventilatory assistance may be useful to make the patient more comfortable, to allow time for medications35 to have an effect; and to provide time for left atrial dilatation to accommodate sudden increases in mitral valve regurgitant volume in patients with acute exacerbation of CVHD (eg, ruptured chordae tendinae with severe cardiogenic pulmonary edema) and impending respiratory failure. More vigorous afterload reduction in patients that can tolerate arterial vasodilation. Drugs potentially beneficial include sodium nitroprusside (starting at 0.5–1 μg/kg/min), hydralazine (0.5–2.0 mg/kg PO), or amlodipine (0.05–0.1 mg/kg PO). Direct vasodilators should be started at a low dosage and up-titrated hourly until adequate clinical improvement accompanied by a decrease of approximately 5–10% in systolic blood pressure is observed. These drugs are recommended in addition to an ACEI and pimobendan. The clinician should be mindful that any decline in blood pressure will also depend on specific vasodilator drug. For example, vasodilation effects are rapid onset with nitroprusside, but slower with amlodipine. Caution is warranted to avoid serious, prolonged hypotension (ie, monitor blood pressure and maintain systolic arterial blood pressure > 85 mmHg or mean arterial blood pressure > 60 mmHg. Serum creatinine concentration should be measured before and 24–72 hours after administration of these drugs. Patients in Stage D have life-threatening heart failure, and a trial of additional afterload reduction is warranted. The panel emphasized that because afterload reduction may increase cardiac output substantially in the setting of severe MR and heart failure, administration of an arterial dilator in this setting does not necessarily decrease blood pressure. No consensus was reached regarding the following acute care Stage D recommendations: Pimobendan dosage may be increased (off-label) to include a 3rd 0.3 mg/kg daily dose. Some panelists administer an additional dose of pimobendan on admission of Stage D patients with acute pulmonary edema. Because this dosage recommendation is outside of the FDA-approved labeling for pimobendan, this use of the drug should be explained to and approved by the client. In animals judged to be too sick to wait for the effects of oral afterload reduction or inotropic support (eg, pimobendan with or without hydralazine or amlodipine), nitroprusside (for afterload reduction in life threatening pulmonary edema) or dobutamine (for inotropic support of the hypotensive patient) must be administered by CRI. Both drugs can be administered at dosages of 0.5–1.0 μg/kg/min and up-titrated every 15–30 minutes to a maximum of approximately 10 μg/kg/min. These drugs, either separately or in combination, can be used for 12–48 hours to improve hemodynamic status and control refractory cardiogenic pulmonary edema. Continuous electrocardiographic and blood pressure monitoring is recommended to minimize the potential risks of this therapy. Sildenafil (1–2 mg/kg PO q12h) is used by a minority of panelists to treat acute exacerbations of Stage D heart failure caused by CVHD, even in the absence of diagnosed pulmonary hypertension. Bronchodilators are recommended as an adjunct therapy in treating cardiogenic pulmonary edema in hospitalized patients by a minority of panelists. Consensus recommendations: Furosemide dosage should be increased as needed to decrease pulmonary edema or body cavity effusions, if use is not limited by renal dysfunction (which generally should be monitored 12–48 hours after dosage increases). The specific strategy and magnitude of dosage increase (eg, same dose increased to 3 times per day versus 2 higher doses, substituting 1 SC dose for a PO dose q48h, or flexible SC dose supplementation based on body weight or girth measurements) varied widely among the panelists. Spironolactone, if not already started in Stage C, is indicated for chronic treatment of Stage D patients. β blockade generally should not be initiated at this stage unless clinical signs of heart failure can be controlled, as outlined in Stage C. No consensus was reached regarding the following chronic Stage D therapeutic recommendations: Hydrochlorthiazide was recommended by several panelists as adjunctive therapy with furosemide, utilizing various dosing schedules (including only intermittent use every 2nd–4th day). Some panelists warned of the risk of acute renal failure and marked electrolyte disturbances, based on personal experience. Pimobendan dosage is increased by some panelists to include a 3rd 0.3 mg/kg daily dose (off-label use, explanations and cautions apply as listed for in-hospital care, above). Digoxin, at the same (relatively low) dosages recommended by some panelists for Stage C heart failure, was recommended for treatment of atrial fibrillation for patients in Stage D, with the same cautions listed in Stage C above. Digoxin, at the same (relatively low) dosages recommended by some panelists for Stage C heart failure, also was recommended by a minority of panelists for all patients in Stage D in sinus rhythm, assuming no clear contraindication was present. Sildenafil (1–2 mg/kg PO q12h) is used by some panelists to treat Stage D heart failure caused by CVHD or to treat advanced CVHD complicated by pulmonary hypertension. The majority of panelists felt that β blockade initiated at an earlier stage of heart failure in CVHD should not be discontinued, but that dose reduction may be needed if shortness of breath could not be controlled by the addition of other medications or if bradycardia, hypotension, or both were present. β blockade still may be useful to decrease the ventricular response rate in atrial fibrillation after stabilization and digitalization. Cough suppressants are recommended by a minority of panelists to treat chronic, intractable cough in Stage D patients receiving home care. Bronchodilators are recommended by a minority of panelists to treat chronic, intractable coughing in Stage D patients receiving home careanelists. Consensus recommendations: All of the dietary considerations for Stage C (above) apply. In patients with refractory fluid accumulations, attempts should be made to further decrease dietary sodium intake if it can be done without compromising appetite or renal function.