Cardiology: Feline Hypertrophic Cardiomyopathy (HCM)

Cardiac diseases in cats are not uncommon. Data on the incidence of cardiac disease in the cat range from >10% - 30%, the least of which are congenital heart defects (only about 1%).
By far the most common cardiac disease in the cat is hypertrophic cardiomyopathy (HCM).

What are the clinical signs of HCM?

A cardiac murmur and/or increased respiratory rate are often the only clinical signs in the early stages of HCM, clinical signs are often even completely absent. Obvious symptoms, on the other hand, usually do not appear until the late stages of HCM.

• Auscultation: cardiac murmurs, gallop rhythm, arrhythmias or without any particular finding
• respiratory symptoms: changes in respiratory type and rate; cyanosis/dyspnea/panting→ panting should always be considered an emergency in the cat!
• Non-specific symptoms such as decreased exercise tolerance, reduced play drive, inappetence, increased sleep (usually more subtle than in dogs).
• circulatory problems: syncope, arterial thromboembolism (ATE) as a consequence
• "cardiac cough" is almost never present in cats

→ Anything from asymptomatic to sudden death is possible!

Since early clear symptoms are often absent, many cats are presented to the veterinarian only at a late stage of HCM or even in the context of an emergency (e.g. ATE, high-grade respiratory distress). Unfortunately, the prognosis is often correspondingly cautious.

Therefore, the goal should be to detect HCM as early as possible, to initiate an individual therapy and to continue with regular follow ups.

Early detection may include:

• Echocardiography: for all cardiac murmurs, possibly exceptions cardiac murmurs up to 2/6 in puppies - "adhesions" possible up to 6th/7th month of life - control! ; predisposed breeds: breeding or pre-anesthetic
• the NT-proBNP test, for example pre-anesthetic
• blood pressure measurement
• regular control of thyroid values (hyperthyroidism ↔ secondary HCM), kidney values
• getting the owners on board: regular counting of the resting respiratory rate!

An intensive auscultation performed without time pressure (cardiac murmurs also possible parasternally) is the base for a careful clinical examination. Some heart murmurs are dynamic and increase with excitement and disappear after a certain period of rest.
Pressing the stethoscope too firmly against the chest can induce a murmur (increase in flow velocity in the pulmonary artery).

→ Not every HCM leads to a heart murmur ↔ not every heart murmur is pathological!

Further diagnostic overview:

• History+clinical examination+ auscultation heart and lungs: form the base
• X-ray: pulmonary edema or thoracic effusions, possibly changes in cardiac silhouette; not suitable for diagnosis of HCM
• Ultrasound: gold standard, for diagnosis of HCM
• NT-pro BNP: as a directional rapid test, e.g. in case of dyspnea or preanesthetic
• ECG: diagnostics of cardiac arrhythmias and heart rate, no reliable statements about potassium/electrolyte level - laboratory diagnostics!
• Genetic tests: do not replace further diagnostics - not every HCM is caused by a genetic defect and there are also cats which are healthy in spite of a genetic defect > generally low significance.

Further examinations in case of diagnosis of HCM
It is essential to look for underlying systemic diseases in manifest HCM (possible differentiation primary vs. secondary HCM).

Baseline values:

• Measurement of blood pressure
• Determination of T4
• Determination of renal parameters

Conversely, if a systemic disease such as hyperthyroidism is diagnosed, a cardiac ultrasound can optimally be performed if it is unclear how long the hyperthyroidism has been untreated.

In conclusion: Overview of the initial measures to be taken in case of dyspnea of the cat

• avoid any stress (owner: presence vs. waiting room)
• X-ray after individual consideration, if necessary prefer short cardiac ultrasound (e.g. focused assessment with sonography for trauma (FAST) or focused Cardiac Ultrasound (FCU)) or wait initially!
• Venous access if possible (Furosemide! ; in case of further worsening of the condition fast emergency care); if impossible: Furosemide i.m.
• Increase oxygen supply: if necessary, secure airway under sedation, otherwise oxygen box
• Thoracentesis if necessary (e.g., lack of breath sounds, severely muffled percussion sound).
• Butorphanol can be used for sedation in case of dyspnea

For more on the classification, diagnosis, and treatment of feline cardiomyopathies, see the ACVIM consensus statement: onlinelibrary.wiley.com/doi/10.1111/jvim.15745

Bibliography: Upon request

Author of the article:

Veterinarian med. vet. Julia Brüner