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Guidelines for the classification, diagnosis, and management of cardiomyopathies in cats

Luis Fuentes V, Abbott  J, Chetboul V, Côté E, Fox P R, Häggströ J, Kittleson MD, Schober K,  Stern JA. ACVIM consensus statement guidelines for the classification, diagnosis, and management of cardiomyopathies in cats. J Vet Intern Med. 2020 Apr 3. 

Cardiomyopathies (diseases of the heart muscle) are amount the most common health conditions in cats. Unlike dogs, valvular heart disease in cats is rare, and most heart disease takes the form of a cardiomyopathy. While in humans and dogs staging and classification guidelines are available, no such system of classification exists in cats. Consensus statement guidelines allow not only for standardization of treatment according to evidence-based guidelines, but also allows for comparison of cases between institutions.

This article represents a consensus statement from the American College of Veterinary Internal Medicine (ACVIM) regarding the diagnosis and management of these cardiomyopathies. It bases these recommendations on a review of veterinary data, relationships to human data and classification schemes, and the opinions of a panel of experts.

The article begins by classifying the forms of cardiac disease and describes several types of cardiomyopathy as below:

  • Hypertrophic Cardiomyopathy (HCM)- The most common type in cats, characterized by thick left ventricular muscle with a non-dilated chamber.
  • Restrictive Cardiomyopathy (RCM)- Normal left ventricular dimensions with atrial enlargement, occurs in endomyocardial (with a prominent bridging scar) or myocardial forms.
  • Dilated Cardiomyopathy (DCM)- Left ventricular systolic dysfunction, normal to reduced wall thickness, and atrial dilation.
  • Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)- Severe right atrial and ventricular dilation, systolic dysfunction, and all thinning.
  • Nonspecific Phenotype- Replaces the previous “Unclassified Cardiomyopathy” (UCM). Does not fit the above categories; the authors report that this should be described in detail.

They also propose a staging system derived from human and canine guidelines; this allows for risks and treatment stratification in cats with cardiomyopathy. The stages are defined as:​​

  • A: Predisposed to cardiomyopathy (ie by breed or family history) but with no clinical or echocardiographic changes.
  • B1: Low risk. These cats show echocardiographic evidence of cardiomyopathy, but have normal or mildly dilated atria and are low risk of eminent Congestive Heart Failure (CHF) or Aortic Thromboembolism (ATE).
  • B2: Higher Risk. As above, however with a moderately to severely dilated atrium and as such at higher risk of CHF/ATE.
  • C: Current or previous CHF or ATE. This applies even if signs have resolved.
  • D: CHF refractory to standard therapy.The authors recommend that genetic testing for cardiomyopathy be pursued in Maine Coon or Ragdoll cats intended for breeding, with less indication in screening for disease occurrence in individual cats.

Diagnostically, a physical exam is minimally useful for detection of subclinical disease (as heart murmurs are not as reliable as in dogs), but may show gallops, arrhythmias, hypothermia, tachypnea, and crackles when clinical.

The diagnostic tests used in CHF are summarized below:

  • NT-proBNP: May be useful in acute CHF, but is not recommended to differentiate normal cats from those with mild-moderate disease.
  • Troponin-I: May be considered for differentiating causes of respiratory distress or to prognosticate.
  • Electrocardiography: Not useful as a screening tool for cardiomyopathy, but should be used for cases of suspected syncope.
  • Blood Pressure: Useful to rule out hypertension as a cause of ventricular hypertrophy.
  • Thyroxine Measurement: Recommended in all cases of abnormal auscultation or hypertrophy in cats over 6 years of age.
  • Echocardiography: The gold standard for the diagnosis of cardiac disease. Should be considered in all diagnosed or suspected cases of cardiomyopathy. The consensus divides into three levels of examination.
    • POCUS: Point of Care Ultrasound used to detect pleural and pericardial fluid, atrial enlargement, subjective contractility, and B-lines. Used in emergent situations or when training precludes full exam.
    • Standard of Care: A thorough ultrasound exam including standard content by a trained, component observer.
    • Best Practice: A scan from a cardiologist with experience in echocardiography including tissue and spectral doppler.

Treatment of cats with CHF is dependant on the stage of disease. In stage A, cats require no therapy. Cats in stage B1 generally need only monitoring, but may be treated with atenolol if there is severe dynamic left ventricular outflow obstruction.

Cats in stage B2 may be treated with clopidogrel to reduce the risk of ATE; if the risk is very high, aspirin and/or a factor Xa inhibitor may be added. ACEIs, spironolactone, and pimobendane are not indicated. If ventricular ectopy is present atenolol or sotalol may be used, and if atrial fibrillation is present diltiazem may also be considered.

Stage C (CHF) should be treated with oxygen, thoracentesis, and furosemide in a crisis. Pimobendan or dobutamine may be considered in a low output state. Nitroglycerin and ACEIs are not recommended. In chronic CHF, furosemide and clopidogrel should be used. Taurine should be measured and supplemented in DCM. Pimobendan may be considered in low output cases without outflow obstruction.

Stage D is considered present when furosemide doses exceed 6mg/kg/day. In these cases, the addition of pimobendan or torsemide may be considered. Low salt diets should be avoided and pimobendan considered in low output states.  Note that as the disease progresses, treatments instituted in the previous stage are likely still needed.

In cases of ATE, treatment is reasonable in animals who are normothermic, have single limb involvement, and have no evidence of CHF. Euthanasia is reasonable in more severe cases. Therapy should include analgesia and anticoagulation with heparin or factor Xa inhibitors in combination with clopidogrel. Thrombolytics are not recommended.

While cardiomyopathies are a diffuse group of disorders, this consensus statement helps to stratify and classify their diagnosis and therapy. (MRK)

See also:

Fox PR, Keene BW, Lamb K, et al. Long-term incidence and risk of noncardiovascular and all-cause mortality in apparently healthy cats and cats with preclinical hypertrophic cardiomyopathy. J Vet Intern Med. 2019;33:2572-2586.

Fox PR, Keene BW, Lamb K, et al. International collaborative study to assess cardiovascular risk and evaluate long-term health in cats 12 LUIS FUENTES ET AL. with preclinical hypertrophic cardiomyopathy and apparently healthy cats: the REVEAL study. J Vet Intern Med. 2018;32:930-943.