ACVIM Feline Cardiomyopathy
Definitions of Cardiomyopathy Phenotypes
Phenotype Definition
Hypertrophic cardiomyopathy (HCM) Diffuse or regional increased LV wall thickness with a nondilated LV chamber.
Restrictive cardiomyopathy (RCM) - Endomyocardial form Characterized macroscopically by prominent endocardial scar that usually bridges the interventricular septum and LV free wall, and may cause fixed, mid‐LV obstruction and often apical LV thinning or aneurysm; LA or biatrial enlargement is generally present.
Restrictive cardiomyopathy (RCM) - Myocardial form Normal LV dimensions (including wall thickness) with LA or biatrial enlargement
Dilated cardiomyopathy (DCM) LV systolic dysfunction characterized by progressive increase in ventricular dimensions, normal or reduced LV wall thickness, and atrial dilatation.
Arrhythmogenic cardiomyopathy (AC), also known as arrhythmogenic right ventricular cardiomyopathy (ARVC) or dysplasia (ARVD) Severe RA and RV dilatation and often, RV systolic dysfunction and RV wall thinning. The left heart may also be affected. Arrhythmias and right‐sided congestive heart failure are common.
Nonspecific phenotype A cardiomyopathic phenotype that is not adequately described by the other categories; the cardiac morphology and function should be described in detail
ACVIM 2020 Consensus Guidelines
Classification
A
Stage A includes cats that are predisposed to cardiomyopathy but have no evidence of myocardial disease
B1
Cats with cardiomyopathy but without clinical signs. Normal/Mild atrial enlargement. Low risk of imminent congestive heart failure (CHF) or arterial thromboembolism (ATE)
B2
Cats with cardiomyopathy but without clinical signs. Moderate/Severe atrial enlargement. Cats at higher risk of imminent congestive heart failure (CHF) or arterial thromboembolism (ATE).
C
Cats that have developed signs of congestive heart failure (CHF) or arterial thromboembolism (ATE), even if clinical signs resolve with treatment.
D
Cats with signs of CHF refractory to treatment.
ACVIM 2020 Consensus Guidelines
Treatment
Stage B1
  • Majority of cats with stage B1 cardiomyopathy will not develop clinical signs.
  • Cats with stage B1 cardiomyopathy are considered at low risk of CHF or ATE, and in general treatment is not recommended.
  • Stage B1 cats shuold be monitored annually for development of moderate to severe LA enlargement (progression to stage B2).
  • Atenolol has not been shown to have any effect on the 5‐year survival rate in cats with subclinical HCM.
Stage B2
  • Cats with stage B2 HCM have an increased risk of developing CHF or ATE.
  • Thromboprophylaxis is recommended when known risk factors for ATE are present.
  • Clopidogrel was more effective than aspirin in cats that had survived a previous ATE episode, therefore Clopidogrel is recommended in cats considered at risk of ATE
  • Cats with stage B2 cardiomyopathy should be monitored for progression of disease.Attention to appropriate handling and minimizing stressful stimuli is important.
  • Neither an angiotensin converting enzyme (ACE) inhibitor (ramipril) nor spironolactone had any effect on LV mass or diastolic function in cats with subclinical HCM. No studies have been reported of pimobendan use in cats with subclinical cardiomyopathy.
  • It is recommended that cats with complex ventricular ectopy be treated with atenolol (6.25 mg/cat q12h PO) or sotalol (10‐20 mg/cat q12h PO;
  • Diltiazem, atenolol or sotalol may be considered in cats with atrial fibrillation and a rapid ventricular response rate.
Stage C
  • Cats with pulmonary edema or pleural effusion caused by CHF usually are presented with tachypnea and labored breathing
  • Empirical diuretic treatment should be considered immediately when the index of suspicion for CHF is high. Supplementary oxygen administration is recommended for any cat with respiratory distress, and sedation with an anxiolytic (eg, butorphanol) also should be considered . Stress should be further minimized by gentle handling, a quiet environment, and provision of a hiding box.
  • Intravenous administration of furosemide, either as multiple boluses of 1 to 2 mg/kg or a constant rate infusion, is recommended for CHF and pulmonary edema in particular.
  • Thoracocentesis should be performed when respiratory distress results from pleural effusion
  • Intravenous fluid treatment is contraindicated in cats with clinically evident congestion, edema or effusion, and can exacerbate signs of CHF even if diuretics are administered concurrently
  • Diuretic treatment is recommended for acute heart failure regardless of the presence of azotemia
  • In cats with signs of low cardiac output (eg, hypotension, hypothermia, bradycardia), PO treatment with pimobendan could be considered, provided dynamic left ventricular outflow tract obstruction is absent In cats with acute heart failure and low cardiac output signs that do no.t show clinical improvement after administration of pimobendan, a constant rate infusion of dobutamine could be considered
  • Administration of nitroglycerin use is not recommended.
  • Angiotensin converting enzyme inhibition is not indicated during acute decompensation of cats with cardiomyopathy.
  • Reevaluation is recommended 3‐7 days after discharge to evaluate for resolution of CHF and to evaluate renal function and serum electrolyte concentrations
Chronic Heart Failure
  • Furosemide is the primary drug used for control of pulmonary edema and effusions in cats with CHF. Typically, treatment consists of furosemide 0.5 to 2 mg/kg PO q8‐12 h, depending on the severity of clinical signs of CHF. A common starting dosage is 1 to 2 mg/kg PO q12h
  • Intravenous administration is preferred in cats with marked respiratory distress from pulmonary edema (see treatment of acute decompensated heart failure, above). The maintenance dose of furosemide should be titrated to maintain a resting or sleeping respiratory rate at home of <30 breaths/min
  • Measurement of serum creatinine, blood urea nitrogen, and electrolyte concentrations is recommended 3‐7 days after initiating furosemide
  • Prophylactic antithrombotic treatment with clopidogrel (18.75 mg/cat PO q24h, with food) is recommended in any cat with a history of CHF and moderate to severe LA enlargement
  • Some cats react to clopidogrel with salivation and retching or vomiting, which can be minimized by administering the medication in an empty gelatin capsule, followed by water.
  • Pimobendan can be considered in cats without clinically relevant left ventricular outflow tract obstruction. A commonly used dosage is 0.625 to 1.25 mg per cat q12h PO.
  • It is recommended that cats with stage C cardiomyopathy be reexamined at approximately 2‐4 month intervals or as needed.
Stage D (refractory)
  • Torsemide may be considered in place of furosemide in cats with persistent CHF despite high doses of furosemide (>6 mg/kg/day PO), at a starting dose of 0.1 to 0.2 mg/kg PO q24h and uptitrating to effect
  • Spironolactone 1 to 2 mg/kg PO q12h to q24h also can be considered for management of chronic CHF. Adverse reactions (eg, ulcerative dermatitis) have been reported in Maine Coon cats treated with spironolactone at a dosage of 2 mg/kg q12h
  • In cats with global LV systolic dysfunction, pimobendan is recommended
  • Taurine supplementation at 250 mg PO q12h also is recommended for cats with global LV systolic dysfunction unless plasma taurine concentrations are in the normal range
  • Foods high in salt should be avoided. As the number of medications increases, owner compliance is likely to decrease, and unnecessary medications should be avoided
  • Cardiac cachexia, defined as loss of muscle or lean body mass associated with heart failure, may be present in cats with stage D cardiomyopathy. Calorie intake should be prioritized over restriction of sodium intake and body condition score should be recorded and an accurate body weight obtained at every clinic visit (LOE low). It is recommended that serum potassium concentration be monitored and if hypokalemia is identified, the diet should be supplemented with potassium from either natural or commercial sources.
Arterial Thromboembolism
  • Most cats with ATE presented to first opinion practice are euthanized
  • If analgesia is adequate and favorable prognostic factors are present (eg, normothermia, only 1 limb affected, absence of CHF), an attempt at treatment can be considered provided the owner is fully informed of the risks and overall poor prognosis.
  • Analgesia is a priority for management of acute ATE in the first 24 hours, and treatment with a mu opioid agonist such as fentanyl, hydromorphone, or methadone is recommended
  • Anticoagulant treatment is recommended using low‐molecular‐weight heparin (LMWH) or unfractionated heparin, or a PO factor Xa inhibitor, which should be started as soon as possible
  • Thrombolytic treatment is not recommended for cats with ATE
  • If CHF is present with ATE, management with furosemide and oxygen is recommended as necessary, but it is important to note that pain also can cause tachypnea, and this should not be mistaken for the presence of CHF.
  • It is recommended that clopidogrel be started as soon as the cat can tolerate PO medications, with an initial loading dose of 75 mg PO (LOE low) followed by 18.75 mg PO q24h. Heparin can be replaced by a PO factor Xa inhibitor in combination with clopidogrel.