Feline HCM and your anaesthesia considerations

Cats with structural heart disease can seem deceptively well…right up until they decompensate. When it comes to anaesthesia, they require a little extra thought and planning.

This article focuses on hypertrophic cardiomyopathy (HCM), including hypertrophic obstructive cardiomyopathy (HOCM), and how to safely approach these cases in general practice.

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Understanding the Disease: Why HCM is different

HCM is a diastolic disorder, not a volume loading condition like mitral valve disease in dogs. Systolic function is often preserved initially, but the thickened myocardium is stiff and can’t relax properly, which leads to:

• Reduced filling and lower cardiac output
• Raised intracardiac pressures, leading to congestive heart failure (CHF)
• Increased sensitivity to tachycardia and volume overload

Key Anaesthetic Considerations

1. Heart Rate

• Avoid tachycardia – it reduces filling time and increases myocardial workload and oxygen demand, which can result in myocardial failure or ischemic damage to the heart muscle.
• In HOCM, fast heart rates worsen obstruction

2. Circulating Volume

• Too high, and the heart can’t accommodate excess preload. These patients can easily be pushed into CHF
• Too low, and the hypovolaemia triggers a reflex tachycardia, worsening output

3. Blood Pressure

• Monitor closely – extremes in either direction can be poorly tolerated
• Correct cautiously to avoid acute destabilisation

Pre-Procedural Screening

ProBNP testing

• Useful in apparently ‘healthy’ cats prior to elective anaesthesia – many cats with HCM do not have heart murmurs, which would ordinarily be an early warning if detected on auscultation.
• Abnormal or elevated values should prompt echocardiography assessment in order to optimise your anaesthetic approach.

Echocardiography

• Can guide fluid plans and drug choices, as well as highlighting those which may benefit from stabilisation prior to procedures.
• Also recommended for cats with known disease if they have not been assessed in the last 6 months.

Owner monitoring

• If the patient is on CHF treatment, ensure owners are tracking sleeping respiratory rate (SRR).
• For stable but cats at risk of developing CHF, baseline SRR trends are useful to monitor in the run-up to procedures to help identify early changes which may signal deterioration.

Medications and Adjustments

Clopidogrel management

• Will increase the risk of intraoperative and post operative haemorrhage
• Patients with a low risk of thrombosis (left atrial enlargement but reasonable left atrial function, not significantly reduced left auricular flow): stop clopidogrel 7 days pre-operatively, restart after final post-op check
• High risk of thrombosis: continue with caution but plan for altered haemostasis (this may be affected by the type of surgery and typical risk of haemorrhage)

Stress management

• Anxious cats are more likely to be tachycardic, but require higher doses of sedation or premedication.
• Alongside the usual cat friendly approaches, pregabalin (given the night before and morning of procedure) is great for anxiolysis and should not affect your drug doses (unless profoundly sedated on pregabalin alone).

Preventing tachycardia

• Propofol is less likely to cause transient tachycardia at induction than alfaxalone
• Optimise analgesia with appropriate opioids and local techniques (nerve/splash blocks) to reduce significant tachycardia and concentration of inhalation agents required

A (surprising) take on alpha-2 agonists

It is very uncommon to hear a cardiologist recommend drugs like medetomidine in cardiac patients, but hear us out. In cats with early, stable disease (without significantly increased left atrial size, poor systolic function or imminent congestive failure) alpha-2s can:

• Reduce heart rate, which improves diastolic filling
• They provide good analgesia and a MAC-sparing effect
• Decrease the pressure gradient across outflow tract obstruction

However:

• If the cat hasn’t had a recent echo or the procedure is urgent, it’s safest to avoid
• Be aware that systolic function will appear artificially reduced if an echo is performed while an alpha-2 is still active

Monitoring and Emergencies

During Anaesthesia

• Continuous ECG and blood pressure monitoring is strongly advised, as well as during the recovery period.
• Occasional single VPCs are generally not a concern if blood pressure remains stable.

In Cardiac Arrest

• Follow RECOVER guidelines as usual.
• In patients with CHF or advanced disease, avoid flushing drugs with large fluid volumes to prevent overload.
• Focus on high-quality compressions and basic life support, which have a far greater impact on survival than the emergency drugs themselves.

Summary

• HCM is a diastolic disease – success depends on heart rate control, careful fluid management, and blood pressure monitoring
• Pre-op screening (especially ProBNP and echocardiography) is essential in higher-risk or undiagnosed patients
• Drug protocols should be tailored to disease severity, not just the presence of a murmur
• Alpha-2 agonists may be helpful in select cases – when in doubt, give us a call

If you have a feline patient with known or suspected cardiac disease and are planning a procedure, we’re here to help with risk assessment, peri-anaesthetic planning, and ongoing case support.

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