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Managing heart disease in cats – part 2

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01 October 2016, at 1:00am

Stephen Collins outlines a recommended approach to cats with suspected heart disease, focusing on common presentations in first opinion practice

FELINE HEART DISEASE IS COMMON, affecting approximately 15% of all cats. In the majority of cases, heart disease is benign, and affected cats remain asymptomatic throughout their lives.

The clinician, however, should not be complacent as heart disease can be life-threatening. When occult disease is suspected, it is important to alert owners of the possible risks, and to discuss options for further investigation with a view to risk assessment and possible prophylactic treatment. 

Clinical signs of heart disease in cats are often severe and sudden in onset; the attendant clinician can be presented with an extremely fragile patient in an emergency setting, where there is a need to make the correct decisions quickly in order to prevent death.

The previous article discussed identification of heart disease in cats and reviewed the merits and disadvantages of various diagnostic modalities (Veterinary Practice, August 2016). This second article outlines a recommended approach to cats with suspected heart disease (occult and overt), focusing on common presentations in rst opinion practice. A series of case studies will follow this article describing the diagnosis and management of feline heart diseases in more detail.

Asymptomatic cats

Prevalence of heart murmurs is high (Cote et al, 2004; Paige et al, 2009; Wagner et al, 2010; Payne et al, 2015); however, a significant proportion of cats with heart murmurs do not actually have heart disease (Paige et al, 2009; Payne et al, 2015). Furthermore, many cats with cardiomyopathy have a normal cardiac auscultation (Wagner et al, 2010; Payne et al, 2015). Echocardiographic examination of every cat with a murmur is not routinely recommended because a significant number of murmurs are “innocent”.

Functional murmurs are usually low grade (I-II/VI); louder murmurs are more likely to be associated with heart disease. Murmurs secondary to cardiomyopathy are often related to left out ow tract obstruction and/or mitral insufficiency.

Out flow obstruction murmurs may have variable intensity, so it is a good idea to listen for at least 30-40 seconds to appreciate this, taking care to listen carefully over the left and right parasternal position where these murmurs are best heard.

The author recommends further investigation in the following situations: 

  • heart murmur grade is III/VI or louder
  • gallop sounds or arrhythmias are detected 
  • any auscultation abnormality is identified in predisposed breeds, for example Maine Coon or Ragdolls

Echocardiography performed by an experienced cardiologist is the test of choice for cats with suspected heart disease; however, cat owners are often reluctant to consider this option for a variety of reasons including cost, travel and lack of concern in an asymptomatic animal.

Cardiac biomarkers (NT-proBNP and cTn-I) can be a useful way of screening for clinically significant disease, sometimes helping the clinician determine which cats warrant further investigation. If cardiac biomarkers are significantly elevated, then echocardiography should be recommended to determine whether heart disease is present and if significant risk factors exist.

Chest radiographs have some value in identifying cardiomegaly where echocardiography is not an option, but the clinician should beware excluding clinically signifcant heart disease on the basis of an apparently normal chest radiograph.

Treatment of asymptomatic cats should never be started unless an echocardiographic assessment has been performed. There is currently no evidence that any treatment modifies natural progression of disease. However, echocardiography will sometimes reveal significant risk factors for individual cats that may warrant treatment: such as left atrial dilation with poor atrial contractility, severe left ventricular hypertrophy and/or severe out ow tract obstruction.

The decision to treat asymptomatic cats is made only after careful consideration of risk versus bene t, taking into account echocardiographic findings and the relative significance of risk factors such as left atrial dilation, also the cat’s character and owner attitudes to administering treatment.

The clinician should remember that regular medication of a cat, often more than once daily, is not a small commitment. The owner should always be made aware that clinical evidence of benefit for treatment of asymptomatic cats does not currently exist, that any recommendation to treat their cat has been based on a considered risk assessment, and there is no guarantee treatment will actually benefit their cat.

Dyspnoeic cats

Dyspnoeic cats present a significant challenge in practice. Affected cats are often in a precarious situation and the clinician’s decision making can be critical if life is to be preserved.

It is important, whenever possible, to determine the cause of dyspnoea before starting treatment. However, cats presenting with severe dyspnoea are often too fragile to tolerate any intervention, therefore the first step must be to deliver oxygen in the least stressful manner until the patient begins to calm. Face masks are often not well tolerated and ow-by piped oxygen is often the safest and most effective option.

A calm environment is important – ideally a quiet room with subdued lighting, staff should take a “hands- off” approach until the cat calms. Sedation (butorphanol) should be considered if the patient is very anxious; however, there is always a risk of respiratory depression which could precipitate a crisis. The clinician should have a well considered plan for emergency measures before the sedation option is taken. Alpha-2 agonists should not be given to patients with cardiac disease.

Ultrasound

Even very stressed cats will usually tolerate ultrasound examination. Where ultrasound is available, the clinician should first establish if the dyspnoeic cat has pleural effusion and/ or an enlarged left atrium. Although a detailed echocardiographic examination of a cat is a difficult skill to master, most clinicians will quickly learn to identify pleural effusion and severe left atrial dilation with minimal training, yielding information that can then help direct clinical approach as follows:

  • Pleural effusion and enlarged left atrium – heart disease and secondary congestive heart failure is the most likely cause of dyspnoea. If pleural effusion is severe, then pleurocentesis should be performed immediately. Chest radiographs should be performed before and after pleurocentesis as pulmonary oedema may also be present and contributing to dyspnoea signs. When congestive heart failure has been diagnosed, medical treatment for congestive heart failure should be started (see below).
  • Pleural effusion and normal left atrium – pleural effusion is probably not cardiogenic and other causes should be considered. Frusemide is usually not indicated. If dyspnoea is severe, then pleurocentesis should be performed and samples submitted for analysis, which is often diagnostically useful in these circumstances. Measuring NT- proBNP (SNAP Feline proBNP) in pleural fluid may be a useful additional rule-out for cardiac disease (Humm et al, 2013). No pleural uid but left atrium is enlarged – heart disease and secondary congestive heart failure manifest as pulmonary oedema may be present and chest radiographs should be obtained. If the patient is too fragile to safely achieve chest radiographs, then frusemide should be given intramuscularly (or intravenously if it can be achieved without further stressing the cat). B-lines seen on ultrasound examination of the lungs (comet-like artefacts indicating sub- pleural pulmonary oedema) will sometimes give a clue that pulmonary oedema is present.
  • No pleural effusion and normal left atrium – congestive heart failure is unlikely. Chest radiographs are indicated. Consider primary respiratory disease, most commonly feline asthma. Observing respiratory pattern will often reveal expiratory effort with asthma; wheezing heard on auscultation is also an indication of asthma and lung pattern is often characteristic. Consider giving a single dose of dexamethasone if the cat is very dyspnoeic and the patient is too stressed to safely obtain radiographs. Although much less common, you should consider other causes of dyspnoea: for example, pulmonary thromboembolism (rare), bronchopneumonia, airway foreign bodies. If ultrasound is not available then chest radiographs are indicated. Pulmonary oedema and pleural effusion are readily identified on chest radiography.

Dyspnoeic cats are often so focused on breathing that chest radiographs can be obtained without sedation. If the cat will not tolerate radiography and if physical examination findings indicate pleural effusion may be present (dull thoracic percussion, muffled heart sounds, inspiratory effort), consider performing pleurocentesis but beware of causing further stress, iatrogenic injury to intrathoracic structures and/ or pneumothorax. NT-proBNP assay (using point- of-care tests such as SNAP Feline proBNP in the emergency setting) can be helpful in discriminating dyspnoea caused by heart disease from non- cardiac causes.

Pleurocentesis - technique

It is important to choose a “safe window”. Ideally, ultrasound should be used to identify the safest position to place a needle or drain, usually the 7-8th intercostal space at approximately level of costo-chondral junction. A short butter y needle with extension line is introduced while applying a small amount of negative pressure using a syringe. Butter y needles should be positioned at against the chest wall to minimise risk of iatrogenic damage.

In an emergency situation, it is not usually necessary to drain both hemi-thoraces and aspirating at least 70-100ml of fluid will significantly palliate dyspnoea signs. Intravenous catheters can be used as an alternative to butter y catheters and are less likely to cause trauma to intrathoracic structures; however, they are inclined to kink and block.

The author prefers to use guidewire-inserted thoracic drains (MILA International), which although more expensive are fairly simple to position, less likely to cause intrathoracic trauma and multiple fenestrations allow for more thorough drainage of pleural fluid.

Longer term management of congestive heart failure

Following diagnosis of congestive heart failure, echocardiography should be performed. Although most cats with heart disease have hypertrophic cardiomyopathy, in fact there is huge phenotypic variability and treatment options are best guided using information obtained from echocardiographic assessment.

Cats diagnosed with congestive heart failure will usually require chronic diuretic therapy; however, it is sometimes possible to reduce or withdraw diuretic therapy altogether in some cases.

Frusemide is generally used at 1-2mg/kg twice daily, but this should always be reduced to minimum effective dose. Response to diuretic therapy should be monitored using echocardiography and chest radiographs; however, minimum effective dose can often be determined using owner observations of resting respiratory rate and effort at home.

Cats with severe left atrial dilation and poor atrial contractility, or cats with history of aortic thromboembolism, should be treated with clopidogrel at 1⁄4 x 75mg once daily which has been shown to improve survival (Hogan et al, 2015). Clopidogrel is not always well tolerated in cats because of its bitter taste, in which case aspirin should be used at 1⁄4 x 75mg every three days, although it is less effective than clopidogrel.

Pimobendan is not licensed for treatment of heart disease in cats but can be useful in the management of advanced heart failure, particularly if systolic dysfunction is present. Care should be taken when obstructive cardiomyopathy is present and the author would only recommend using pimobendan having performed an echocardiographic examination.

Angiotensin-converting enzyme inhibitors and spironolactone can be useful in management of chronic congestive heart failure. Their benefit is well established in people and dogs but studies are lacking in cats.

Feline aortic thromboembolism (FATE) 

Aortic thromboembolism is perhaps the most catastrophic complication of feline heart disease and euthanasia is commonly recommended in practice. Various studies have shown cats presenting with FATE have poor prognosis (Borgeat et al, 2015; Rush et al, 2002); however, a proportion of cats will recover and subsequently enjoy normal quality of life with appropriate treatment. Negative prognostic indicators are ≥ two limbs affected and hypothermia on presentation.

Cats with FATE typically present in severe distress, having lost the use of one or both hindlimbs secondary to occlusion of iliac arteries (saddle thrombus). They can be mistaken as road traffic accident victims; however, careful clinical examination will usually reveal absent femoral pulses and pale hind limb extremities. Thromboemboli can affect other arteries, most commonly the left brachial which can present as forelimb paresis/ lameness; however, other arteries such as renal and cerebral can also be affected, making for a complex clinical presentation.

Treatment is focused on pain relief (methadone or morphine are preferred where available, but more generally available opiates such as buprenorphine should be considered a minimum). Tachypnoea signs, although usually related to pain and anxiety, can also be caused by concurrent congestive heart failure, which is often present and requires management with diuretics.

Treatment to prevent further development of the thrombus with clopidogrel is recommended. Unfractionated heparin (or low molecular weight heparin if available) can also be used; however, heparin was not associated with improved survival in one large study of cats with FATE (Borgeat et al, 2014). Secondary neuropathies are common in severe cases. Sudden death can occur secondary to reperfusion injury (hyperkalaemia secondary to tissue hypoxia).

Uncommon presentation for heart disease in cats

  • Collapsing and syncope

Cats will occasionally present with collapse or syncope signs secondary to heart disease. The mechanism for collapse is not always clear, but is probably related to arrhythmia in most cases. Significant hypotension can sometimes occur with left ventricular out ow tract obstruction seen with hypertrophic obstructive cardiomyopathy, which can manifest as weakness or lethargy.

  • Sudden death

The true incidence of sudden death secondary to heart disease is unknown in cats. However, in a recent pathology study of 158 cats with unexpected death, necropsy revealed no other cause other than cardiac disease in 55% of cases. Another study (Payne et al, 2013) reported sudden death in 17/107 cats that died as a result of HCM. 

Key points

Heart disease is common. Clinical signs of heart disease in apparently healthy cats should be investigated, especially if murmur grade is ≥ III/VI, gallop sounds and/or arrhythmia are detected.

Thoracic ultrasound is usually well tolerated and safe, making it an invaluable tool for the initial assessment of dyspnoeic cats. Echocardiography is the most useful diagnostic test for investigation of heart disease and helps determine optimal treatment plans for individual cats. Feline ATE is a catastrophic event and clopidogrel should be used to reduce risk when left atrial enlargement is detected.

  • The full list of references is available on request from editor@veterinary- practice.com.