Feline cardiomyopathies are common in the general cat population, with reports assessing prevalence at around 15 percent (Payne et al., 2015). Cardiomyopathy is also a leading cause of death, with one study showing that cardiac disease was the eighth most common cause of death in cats in general practice (O’Neill et al., 2015). For a diagnosis of cardiomyopathy to be made, the myocardium is judged to be structurally and functionally abnormal, in the absence of any other cause. In such cases, the veterinary nurse has a critical role in being the advocate for the patient and client support.
Clinical diagnosis of feline cardiomyopathies
Recently, the American College of Veterinary Internal Medicine (ACVIM) published a consensus statement on feline cardiomyopathies, with the aim of helping veterinary surgeons diagnose and manage cats with heart disease (Luis Fuentes et al., 2020). The statement classified feline cardiomyopathies on phenotypic appearance, thus moving the focus from a genetic approach to a clinical one.
The consensus statement identified five phenotypes:
- Hypertrophic cardiomyopathy (HCM)
- Restrictive cardiomyopathy (RCM)
- Dilated cardiomyopathy (DCM)
- Arrhythmogenic cardiomyopathy (AC)
- Non-specific phenotype
Hypertrophic cardiomyopathy
HCM is the most commonly diagnosed phenotype in cats. It is characterised by a thickened left ventricle (LV), which can either be localised or diffuse, but the LV is not dilated. Before a diagnosis of HCM can be made, other diseases such as hyperthyroidism and hypertension, which can give an appearance of HCM, must be excluded.
Before a diagnosis of HCM can be made, other diseases such as hyperthyroidism and hypertension, which can give an appearance of HCM, must be excluded
Restrictive cardiomyopathy
Two types of RCM are described. The first is endomyocardial, where an endocardial scar can be visualised on diagnostic imaging, and which may form a bridge between the LV free wall and interventricular septum. Occasionally this may cause an obstruction in the left ventricle and there may be left ventricular thinning noted. Left atrial (LA) or biatrial enlargement may also be present. The second type of RCM reported is the myocardial form. This is said to occur when the LV is within normal dimensions, but there is LA or biatrial enlargement.
Dilated cardiomyopathy
DCM is characterised by LV systolic dysfunction and increased LV dimensions. LV walls may reduce in thickness or stay the same, but the reduction is accompanied by atrial dilation.
Arrhythmogenic cardiomyopathy
Also known as arrhythmogenic right ventricular cardiomyopathy (ARVC), AC is characterised by right atrial and right ventricular (RV) dilation, RV systolic dysfunction and RV wall thinning. Arrhythmias are common, as is right-sided congestive heart failure.
Non-specific phenotype
This refers to myocardial disease that does not fit the above categories.
It is important to note that while these different phenotypes have been recognised, it is possible that the phenotypical group may change, for example if the disease progresses.
It is important to note that while these different phenotypes have been recognised, it is possible that the phenotypical group may change, for example if the disease progresses
Classification of heart disease and nursing care
The ACVIM consensus statement also introduced a classification system based on the canine degenerative myxomatous mitral valve disease classification (Keene et al., 2019). The feline cardiomyopathy classification system has four stages, allowing for appropriate nursing actions to be taken at each.
Stage A
This group includes cats that are predisposed to heart disease because of their breed but present no evidence of disease. If the cat is to be bred from, regular echocardiographic screening is recommended. Nursing consideration at this stage is to encourage optimal nutrition, as with all cats.
Stage B
Cats in this group have been diagnosed with cardiomyopathy (for example, because of increased LV thickness), but crucially, no clinical signs are yet present. Stage B is divided into two categories based on risk associated with LA size:
B1 includes cats that are at low risk of congestive heart failure (CHF) or aortic thromboembolism (ATE). LA size is either within normal limits or mildly increased. Nursing care at stage B1 is to support the owner, making them aware of their cat’s exercise tolerance and normal appetite and start to be aware of their cat’s sleeping respiratory rate (SRR). These disciplines will establish a benchmark for the individual.
B2 includes cats that are at higher risk of imminent CHF or ATE because LA size is moderately to severely increased. Other findings include possible arrhythmias, gallop rhythm, poor LA function, spontaneous echo contrast or intracardiac thrombus.
At stage B2, owners will most likely be administering the antiplatelet drug clopidogrel. This drug has been shown to be the most challenging medication to administer (Murphy et al., 2022). Therefore, in addition to the nursing recommendations for B1, nurses might discuss medication compliance for cat and owner.
Stage C
This is a diverse group consisting of cats that have current signs or have had previous signs of CHF or an ATE. Cats can present either with acute life-threatening heart failure or in extreme and acute pain due to a thrombus, or be living with chronic heart failure. The most common clinical sign of a cat in heart failure is laboured breathing. This can be tachypnoea, dyspnoea or orthopnoea. Some cats may only show non-specific signs such as hiding or inappetence. Syncope can occur, but is less common, and often history is unremarkable. Sudden death can be the first clinical sign.
Again, an ATE can be the first clinical sign of heart disease, which can be very distressing for the owner. Importantly, cats with an ATE can also have concurrent CHF. The nursing role is pivotal at stage C
Cats that have had a thrombotic event may present with paresis or paralysis and be in extreme pain. One study reported that the most common presentation was both hindlimbs being affected (Borgeat et al., 2014). Other signs may be present, depending upon where the thrombus has terminated. Again, an ATE can be the first clinical sign of heart disease, which can be very distressing for the owner. Importantly, cats with an ATE can also have concurrent CHF. The nursing role is pivotal at stage C.
Nursing the acute feline heart failure patient
Immediate nursing care of the cat in respiratory distress includes:
- Minimising stress
- Supplemental oxygen
- Administration of diuretics – intramuscular until intravenous (IV) access can be gained safely
- Monitoring respiratory rate and effort every 15 to 30 minutes to assess diuretic efficacy
- Possible sedation to decrease myocardial oxygen demand
- Preparing equipment in case thoracocentesis is required
- Checking and changing bedding as necessary, alongside recording estimated urine output
- Providing water
Diagnostic tests should allow for rest periods and should be performed in order of priority, to be decided between the veterinary surgeon and nurse. Diagnostic tests that may be required include physical examination; brief echocardiography or a thoracic-focused assessment with sonography for triage (TFAST); assessing for abnormal fluid accumulation and LA size; blood pressure measurement to assess cardiac output; and haematology, biochemistry and possibly T4, to rule out concurrent disease and benchmark renal parameters and electrolytes.
The ACVIM consensus statement recommends that cats are discharged as soon as they have been stabilised. Owners should be encouraged to record SRR and call the vet if it exceeds 30 breaths per minute, in case the diuretic dose needs to be adjusted. Appetite should also be monitored closely. It is recommended that the cat is rechecked between three and seven days to assess renal parameters and for the resolution of CHF, but additional stress to the cat needs to be considered.
Nursing the chronic feline heart failure patient
Owner and cat compliance is necessary to manage CHF. Regular check-ins can identify medication problems quickly and monitor SRR. Vet rechecks are advised between two and four months, but stress to the cat must be taken into consideration (Luis Fuentes et al., 2020).
Nursing the cat with an ATE
Clinical signs of an ATE include:
- Acute onset of pain due to paralysis or paresis
- Loss of peripheral pulses in the affected limb(s)
- Tissue pallor
- Cold extremities of affected limb(s)
- Signs of heart failure including respiratory distress (remembering that pain can also cause tachypnoea)
- Hypothermia
Euthanasia is often the outcome of a thrombotic event. If the cat is to be treated, pain management is key for ATE management. Methadone is recommended for at least the first 24 hours, and anticoagulant therapy should be initiated (Luis Fuentes et al., 2020). If CHF is present, oxygen and diuresis will also be needed. Prognosis is associated with hypothermia, so the temperature of the patient should be taken soon after admission and the administration of analgesia. Heat sources are not recommended because the cat may not be able to move itself away.
If the cat is to be treated, pain management is key for ATE management. Methadone is recommended for at least the first 24 hours, and anticoagulant therapy should be initiated
When the patient has been stabilised, appetite should be monitored and the affected limbs checked for necrosis. Gentle passive movement of the affected limbs can begin and electrolytes should be monitored. Re-examination is recommended every one to three months while, again, assessing the risk of stress to the cat.
Stage D
Cats in this class have become refractory to standard heart failure therapy. The vet may change from furosemide to torasemide, and other medications may be added in, such as the potassium-sparing diuretic spironolactone. Nurse considerations include managing the owner and patient to prevent stress, as acute and life-threatening heart failure, or another ATE, can occur at any time. Appetite, body and muscle condition scoring can be done, alongside quality-of-life discussions with the owners.
Summary
Client communication is crucial to the often-terminal nature of CHF and ATE. The severity of clinical signs can often be a shock, and nurses are ideally placed to support owners. In the earlier stages of heart disease, nurses can educate clients to monitor exercise, SRR and appetite.
