Monday, June 15th, 2020
The American College of Veterinary Internal Medicine frequently publish consensus statement guidelines on a wide variety of topics from large and small animal medicine. They are all written by experts in their field and provide some really handy guidelines for veterinary professionals to follow, ensuring that you are managing your cases to the highest standard. What is even better is that they are all free to access from the Journal of Veterinary Internal Medicine. Feline cardiomyopathies is the most recent published consensus statement.
I thought it might be useful to summarise this document, in particular changes that have been suggested to the way in which we think about and manage feline heart disease.
Classification of diseases
Suggested changes to the way in which we classify feline heart disease are discussed. The old classification system was as follows:
- Hypertrophic cardiomyopathy (HCM)
- Restrictive cardiomyopathy (RCM)
- Dilated cardiomyopathy (DCM)
- Arrhythmogenic right ventricular cardiomyopathy (ARVC)
- Unclassified cardiomyopathy (UCM)
This consensus statement has suggested that we keep these names EXCEPT for UCM and that we add the word ‘phenotype’ after each one e.g. HCM phenotype. Unclassified cardiomyopathy will now be called ‘nonspecific phenotype’ – this is a phenotype that does not fit into the other classification systems. It should be described based on morphology and function on echocardiography so that changes over time can be tracked.
Classifications can change over time such that a cat with HCM can develop RCM towards the later stages. They have also suggested that in cases where we document hyperthyroidism that we would call this ‘HCM phenotype in conjunction with hyperthyroidism’.
A new staging system has been proposed, similar to the mitral valve disease one in dogs. It is as follows:
- Stage A – predisposed breeds without evidence of myocardial disease
- Stage B1 – subclinical – normal/ mild atrial enlargement
- Stage B2 – subclinical – moderate/ severe atrial enlargement
- Stage C – current/ previous heart failure/ thromboembolism
- Stage D – refractory heart failure
The consensus statement focuses more on HCM as it is the most commonly encountered feline heart disease.
Cats with HCM tend to be older, male cats with a loud systolic murmur (although HCM can be seen in young cats, females and cats without a murmur). Some breeds are predisposed such as the Maine Coon, Ragdoll, British Shorthair, Bengal, Persian, Sphynx etc. Mutations in the sarcomeric genes have been identified in Maine Coon and Ragdoll breeds.
Prognosis is difficult to establish as many cats have HCM and remain symptom free for their life. A younger age at diagnosis and lack of clinical signs favour a better prognosis. Gallop sounds, atrial enlargement, reduced systolic function, extreme hypertrophy etc all carry a worse prognosis.
- Genetic testing is advised in Maine Coon and Ragdoll cats intended for breeding.
- Cats homozygous for a mutation should not be bred from.
- Cats negative for the mutation can still develop HCM and should be regularly screened.
- Radiography is insensitive for the diagnosis of mild-moderate HCM.
- If radiographs cannot be obtained safely they should be delayed in favour of thoracic ultrasound.
- NT-proBNP is not advised for differentiating normal cats from cats with mild-moderate disease, it is only useful if the cat has severe disease.
- Total T4 should be evaluated in any cat >6yrs of age.
- Doppler echo is the gold standard test.
- Protocols for echocardiography from basic to advanced are outlined in the document (see the link for these). They vary from a focused point-of-care examination to standard of care and best practice (Doppler).
- Echo should be considered for a cat with gallop sound, murmur or arrhythmia.
- Point-of-care ultrasound should be considered in any cat that is dyspnoeic and is the diagnostic method of choice to minimise stress.
- Stage B1 – no treatment but should be monitored annually.
- Stage B2 – increased risk of heart failure/ thromboembolism. Clopidogrel should be considered in cats at risk of thromboembolism i.e. smoke (spontaneous echo contrast), moderate to severe atrial enlargement etc. They should be monitored for development of disease and clinical signs. No other treatment indicated unless complex arrhythmias.
- Stage C:
- Acute – Oxygen, butorphanol, intravenous furosemide (boluses 1-2 mg/kg or CRI), AVOID fluids and beta-blockers, thoracocentesis if pleural effusion, if low output signs pimobendan orally can be considered (off-licence use in cats) and or dobutamine. Monitor renal values and electrolytes, including after discharge.
- Chronic – oral furosemide titrated to maintain a sleeping/ resting respiratory rate <30 breaths per minute. Ace inhibitors can be used, but a recent study showed lack of efficacy. Clopidogrel should be started. Re-examine every 2-4 months, if possible.
- Stage D – can consider torasemide (off licence) and spironolactone (adverse reactions have been documented in the Maine Coon). Use taurine if DCM. Prioritise calorie intake.
- Thromboembolism – opioid analgesia (avoid NSAIDs), anti-coagulant medication, clopidogrel.
We have webinars on feline cardiomyopathies and aortic thromboembolism on our website that give more information on diagnosis and management of these disease processes.