Hypertrophic Cardiomyopathy (HCM) in Cats – NAVLE Notes

Hypertrophic Cardiomyopathy (HCM) in Cats (NAVLE Notes)

Hypertrophic cardiomyopathy (HCM) is the most common cardiac condition in cats, leading to thickening of the left ventricular wall and sometimes sudden death due to thromboembolism. It often presents in specific breeds with varying severity.

Classic Case

• Signalment:
• Typically affects adult cats, with males at higher risk.
• Predisposed breeds: Maine Coons, Ragdolls.
• Signs:
• Often asymptomatic until sudden death.
• May present with tachypnea, dyspnea, or hind limb paralysis (paraplegia) due to thromboembolism.
• Murmurs or arrhythmias are usually absent.

Diagnosis

• Precautions:
• Avoid stressing dyspneic or tachypneic cats; perform only necessary diagnostics.
• Thoracic Radiography:
• DV view often preferred.
• Findings: Cardiomegaly, dilated left atrium, pulmonary edema, and pleural effusion.
• Echocardiography (M-mode):
• Left ventricular wall thickening and papillary muscle hypertrophy.
• Systolic anterior motion (SAM) of the mitral valve.
• Echo contrast (“smoke”) in dilated left atrium, indicating RBC swirling and a high risk of thromboembolism.
• Screening Tests:
• Plasma NT-proBNP: Detects occult HCM (requires echo confirmation).
• Genetic Testing: MYBPC3 gene mutations (A31P or A74T for Maine Coons, C820T for Ragdolls).

Treatment

• Congestive Heart Failure (CHF):
• Supplemental oxygen for dyspnea/tachypnea.
• Diuretics: Lifetime loop diuretic therapy.
• ACE Inhibitors: Enalapril may be beneficial.
• β-blockers (e.g., atenolol) if left ventricular outflow obstruction is seen on echo.
• Thromboembolism:
• In Hospital: Heparin for anticoagulation and analgesia.
• At Home: Clopidogrel (Plavix®) to prevent thromboembolism, and enoxaparin if treating an existing thromboembolism.

Key Points

• Prognosis:
• Generally poor to fair, depending on disease severity and response to treatment.
• Cats in CHF are often hypothermic and require close monitoring.
• Breeding Considerations:
• Genetic testing is essential in predisposed breeds.
• Do not breed homozygous cats for the MYBPC3 gene mutations.

---

NAVLE-Style Practice Questions on Hypertrophic Cardiomyopathy

Question 1
A 5-year-old Maine Coon presents with sudden dyspnea and tachypnea. Thoracic radiographs reveal cardiomegaly and pulmonary edema. What is the most likely diagnosis?

• A) Asthma
• B) Hypertrophic cardiomyopathy
• C) Chronic bronchitis
• D) Pleural effusion

Correct Answer: B
Explanation: Maine Coons are predisposed to HCM, which can cause sudden dyspnea due to CHF and pulmonary edema. Radiographic findings of cardiomegaly support this diagnosis.

---

Question 2
A Ragdoll cat has been diagnosed with hypertrophic cardiomyopathy and is at home on Clopidogrel. What is the purpose of this medication?

• A) To manage CHF
• B) To treat pulmonary edema
• C) To prevent thromboembolism
• D) To lower blood pressure

Correct Answer: C
Explanation: Clopidogrel (Plavix®) is an anticoagulant used to prevent thromboembolism, a common complication in cats with HCM.

---

Question 3
An adult male cat with HCM and CHF presents with dyspnea and hypothermia. What is a recommended part of immediate management?

• A) Furosemide
• B) Antibiotics
• C) ACE inhibitors only
• D) Surgical intervention

Correct Answer: A
Explanation: Furosemide, a loop diuretic, is commonly used to manage fluid overload in CHF. Immediate CHF management also involves supplemental oxygen and minimizing stress.

For study notes visit cracknavle.com