FELINE

Welcome to the Feline NAVLE Notes: Cardiorespiratory section on AllVetsLink.

Diseases of the feline cardiorespiratory system require careful clinical assessment, as conditions like hypertrophic cardiomyopathy, feline asthma, and pleural effusion often present with subtle or nonspecific signs, demanding species-specific diagnostic and treatment strategies for NAVLE readiness.

Notes:

Feline Hypertrophic Cardiomyopathy (HCM)

🫀 Feline Hypertrophic Cardiomyopathy (HCM) is the most prevalent form of heart disease in cats and a critical condition to understand for NAVLE preparation. It is characterized by primary concentric hypertrophy of the left ventricular myocardium, typically in the absence of other systemic causes such as hypertension or hyperthyroidism. HCM can lead to diastolic dysfunction, left atrial enlargement, congestive heart failure (CHF), and predisposition to arterial thromboembolism (ATE)—particularly saddle thrombus formation. Commonly affected breeds include Maine Coons and Ragdolls, often with an autosomal dominant genetic mutation in the myosin-binding protein C (MYBPC3) gene. Clinical manifestations range from asymptomatic murmurs to severe respiratory distress and sudden death. Diagnosis is based on echocardiography, and treatment focuses on controlling heart rate, improving diastolic filling, and preventing thromboembolic events.

Feline Aortic Thromboembolism

🐾 Comprehensive Information on Feline Aortic Thromboembolism (FATE / CATE) for NAVLE Preparation 🐾 Feline Aortic Thromboembolism (FATE), also known as Cardiogenic Arterial Thromboembolism (CATE) or “saddle thrombus,” is a life-threatening condition in cats characterized by the embolization of a cardiac thrombus—most often originating in a dilated left atrium—into systemic arteries, especially the terminal aorta. It is most commonly associated with underlying cardiomyopathies, particularly Hypertrophic Cardiomyopathy (HCM). Affected cats present acutely with hindlimb paralysis, pain, absent pulses, and hypothermia due to ischemic neuromyopathy. This condition is a true emergency requiring rapid diagnosis, stabilization, and aggressive multimodal treatment to reduce morbidity and mortality. This note provides a detailed and clinically focused overview of the etiology, pathophysiology, clinical signs, diagnostic approach, treatment options (including anticoagulation and thrombolysis), prognosis, and preventive strategies. It is intended to prepare veterinary professionals for recognizing and managing FATE with confidence during the NAVLE and in clinical practice.

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Explore additional sections of the NAVLE Feline Notes:

Cardiovascular

Respiratory

Internal
Medicine

Endocrine

Nervous

Musculoskeletal

Infectious Diseases
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Preventive Medicine

Pathology

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NAVLE Flash Cards

FlashCards

Feline Cardiorespiratory

Question 1:

A 6-year-old male neutered domestic shorthair cat presents with sudden onset vocalization, hindlimb paralysis, and respiratory distress. Physical exam reveals absent femoral pulses bilaterally, cyanotic nail beds, cold extremities, and a rectal temperature of 36.5°C. A loud gallop rhythm is auscultated. Which of the following best explains the pathophysiologic process responsible for the cat’s clinical signs?

A. Immune-mediated myositis
B. Saddle embolism originating from atrial thrombus formation secondary to cardiomyopathy
C. Spinal cord compression from intervertebral disc herniation
D. Vasculitis associated with systemic lupus erythematosus

Question2:

Which of the following treatment strategies offers the most appropriate long-term management for a cat recovering from a first episode of feline aortic thromboembolism (FATE), and what is the expected prognosis?

A. NSAIDs and aspirin alone; excellent long-term prognosis if CHF is not present
B. Clopidogrel plus rivaroxaban; guarded prognosis, especially in bilateral limb cases
C. Warfarin and physical therapy; curative with low risk of recurrence
D. Heparin infusions indefinitely; prognosis depends only on response to analgesia

Question 3:

A 4-year-old neutered male Maine Coon cat presents for evaluation after a murmur was noted during a routine checkup. The cat is asymptomatic. On echocardiography, marked concentric hypertrophy of the left ventricle is noted without left atrial enlargement. What is the most likely diagnosis?

A. Dilated cardiomyopathy
B. Hypertrophic cardiomyopathy
C. Restrictive cardiomyopathy
D. Hyperthyroidism-induced cardiomyopathy

Question 4:

A 7-year-old domestic shorthair cat is diagnosed with hypertrophic cardiomyopathy and moderate left atrial enlargement. The cat presents with mild tachypnea and a gallop rhythm. Which of the following is the most appropriate initial medical therapy?

A. Pimobendan and enalapril
B. Furosemide, atenolol, and clopidogrel
C. Lidocaine and spironolactone
D. Benazepril and digoxin

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Flash Cards - Answers

Question 1:

Answer: B) Saddle embolism originating from atrial thrombus formation secondary to cardiomyopathy

📘 Explanation:
This cat presents with classic clinical signs of Feline Aortic Thromboembolism (FATE), also known as Cardiogenic Arterial Thromboembolism (CATE). The most common underlying cause is Hypertrophic Cardiomyopathy (HCM), which results in impaired left ventricular filling, elevated left atrial pressures, and left atrial dilation. These conditions predispose to thrombus formation in the left atrium, satisfying Virchow’s triad: blood stasis, endothelial injury, and a hypercoagulable state.

The thrombus often embolizes to the aortic trifurcation ("saddle thrombus"), leading to acute bilateral pelvic limb ischemia, pain, paresis/paralysis, absent pulses, and cold extremities. Gallop rhythms and signs of CHF (e.g., dyspnea, crackles) often accompany FATE.

This is a vascular event, not a neurologic or immune-mediated condition, and requires emergency stabilization, including analgesia, anticoagulation, and management of underlying cardiac disease.

Question2:

Answer: B) Clopidogrel plus rivaroxaban; guarded prognosis, especially in bilateral limb cases

📘 Explanation:
The cornerstone of long-term FATE management includes dual antithrombotic therapy, most effectively with clopidogrel (18.75 mg PO q24h) and a direct oral anticoagulant like rivaroxaban (0.5–1 mg/kg PO q24h). Clopidogrel inhibits platelet aggregation via P2Y12 receptor blockade, while rivaroxaban is a Factor Xa inhibitor, providing anticoagulant action without the need for INR monitoring (unlike warfarin).

Studies show that dual therapy reduces recurrence better than monotherapy. Warfarin is less commonly used due to narrow therapeutic index and monitoring challenges.

The prognosis is guarded:

Bilateral pelvic limb involvement has a lower survival to discharge (~37.5%).
Factors such as limb lactate >11.5 mmol/L and rectal temperature <37°C are associated with poor outcome.
Median survival post-discharge is 350–500 days with appropriate therapy and cardiomyopathy management.
NSAIDs are not indicated, and while heparin may be used acutely, it is not suitable for long-term control.

Question 3:

Answer: B) Hypertrophic cardiomyopathy

📘 Explanation:
Hypertrophic Cardiomyopathy (HCM) is the most common cardiac disease in cats and is characterized by concentric hypertrophy of the left ventricle in the absence of systemic hypertension or hyperthyroidism. It results in diastolic dysfunction due to impaired myocardial relaxation and increased ventricular stiffness.
It is most frequently observed in Maine Coon and Ragdoll cats, often with a genetic mutation in the MYBPC3 gene (myosin-binding protein C).
Diagnosis relies heavily on echocardiography, which shows:

Increased left ventricular wall thickness
Normal or small ventricular chamber size
+/- Left atrial enlargement (a prognostic indicator)

Cats may be asymptomatic, or clinical signs may include a murmur, gallop rhythm, or sudden onset dyspnea if CHF or thromboembolism develops.
Important differentials to rule out include hyperthyroidism and systemic hypertension, which can also cause myocardial hypertrophy but are secondary.

Question 4:

Answer: B) Furosemide, atenolol, and clopidogrel

📘 Explanation:
In cats with symptomatic HCM and evidence of left atrial enlargement or early CHF, medical therapy is indicated to reduce preload, slow heart rate, and reduce thromboembolic risk.

Furosemide is a loop diuretic that reduces pulmonary edema by decreasing preload.
Atenolol is a beta-1 selective blocker that slows the heart rate, allowing for better ventricular filling during diastole.
Clopidogrel is an antiplatelet agent (P2Y12 receptor antagonist) that prevents arterial thromboembolism, especially in cats with atrial enlargement or prior thromboembolic events.

Pimobendan is generally avoided in cats with HCM due to its inotropic effects, which may worsen outflow tract obstruction. ACE inhibitors like benazepril or enalapril may be added in chronic management but are not first-line in acute settings.

Prognosis depends on the severity of atrial enlargement, the presence of CHF or arterial thromboembolism, and response to therapy. Sudden death remains a risk in advanced cases.