Feline Hypertrophic Cardiomyopathy (HCM)

• Feline cardiovascular health encompasses arrhythmias (covered in the dog section) and various cardiomyopathies.

Hypertrophic Cardiomyopathy (HCM)

• Primary HCM is idiopathic, often autosomal dominant (especially in Maine Coons), and typically affects young adult male cats without warning signs.
• Secondary HCM involves left ventricular (LV) and/or right ventricular (RV) concentric hypertrophy.
• Secondary HCM causes include pressure overload (aortic stenosis, systemic hypertension), hyperthyroidism (leading to left-sided congestive heart failure/L-CHF), hypertension from chronic renal disease (L-CHF), high-altitude disease in cattle (right-sided congestive heart failure/R-CHF), heaves in horses (R-CHF), and heartworm in dogs (R-CHF).
• Specific mutations in Maine Coons (A31P) and Ragdolls (R820W) are linked to primary HCM.
• HCM affects all breeds, but Maine Coon, Ragdoll, Sphynx, and Bengal breeds are more commonly affected.
• Clinical signs include symmetric or asymmetric LV wall thickening, normal LV systolic function, left atrial enlargement (LAE), aortic thromboembolism, dyspnea, or tachypnea.
• Non-cardiac causes of LV hypertrophy include systemic hypertension, hyperthyroidism, acromegaly, and dehydration (causing pseudohypertrophy).
• Diagnosis of HCM relies on echocardiography, looking for LA enlargement (LA:Ao > 1.2 is abnormal, <5mm is normal) and systolic anterior motion (SAM) of the mitral valve.
• SAM can cause mitral valve regurgitation, increasing the workload on the left atrium.
• Treatment for mild HCM involves beta-blockers or calcium channel blockers.
• Advanced HCM treatment includes low-dose aspirin/clopidogrel, diuretics, and ACE inhibitors.
• HCM can lead to diastolic dysfunction, LA/LV thickening, L-CHF, and turbulent blood flow/stasis, increasing the risk of blood clots (LA and saddle thrombus).

Restrictive Cardiomyopathy (RCM)

• RCM is characterized by decreased contractility and impaired ventricular filling due to reduced compliance (often from fibrosis).
• Ventricles are usually normal in size, but both atria are often dilated.
• RCM predisposes cats to clot formation and left- or bilateral heart failure.
• Primary RCM is potentially linked to myocardial eosinophils, viral infections, immune-mediated myocarditis or vasculitis, causing cycles of injury and repair with fibrosis, and genetic causes (TnT or TnI mutations).
• Secondary RCM is associated with amyloidosis and storage diseases.
• RCM is more common in DSH, Birmans, Siamese, and Persian breeds.
• Clinical signs of RCM include asymmetric LV wall thinning (with or without dilation), normal to mildly reduced LV systolic function, biatrial enlargement, severe LA enlargement, and severe LV diastolic dysfunction (restrictive filling).
• Diagnosis of RCM relies on echocardiography.

Dilated Cardiomyopathy (DCM)

• DCM is caused by taurine deficiency, although is now uncommon. Siamese, Burmese, and Abyssinian breeds are predisposed.
• DCM shares similar clinical signs, diagnostic approaches, and treatments as DCM in dogs.
• Prevention of DCM focuses on feeding cats a balanced diet.

Heartworm Disease

• Heartworm disease is caused by Dirofilaria immitis and is transmitted by mosquitoes.
• Clinical signs in cats include vomiting, intermittent cough, increased respiratory rate, and sudden death.
• Diagnosis involves radiography (though only 50% show changes seen in dogs, sometimes mimicking bronchitis or asthma), antigen testing (false negatives possible), antibody testing (positive indicates past infection), and echocardiography (worms may be visible in the pulmonary artery).
• Treatment involves prednisolone to manage lung changes, as melarsomine is not recommended.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

• ARVC is a rare form of cardiomyopathy, accounting for 1-2% of cases in cats.
• Morphological characteristics of ARVC are right atrial/ventricular dilation, right ventricular systolic dysfunction, normal to mildly reduced LV functions, and ventricular (more than supraventricular) arrhythmias.

Congenital Abnormalities

• Patent Ductus Arteriosus (PDA) is rare in cats.
• Clinical signs of PDA include a continuous left base murmur described as a "washing machine" murmur and left-sided CHF.
• Diagnosis involves radiography (left atrial and ventricular enlargement, distinct pulmonary artery and ascending aorta, ductus bulge) and echocardiography (variable left atrial and ventricular dilation, continuous turbulent blood flow in the pulmonary artery, visible ductus emptying into the pulmonary artery).
• Treatment for PDA involves surgical ligation (transarterial occlusion).
• Eisenmenger syndrome is caused by a reversed PDA where severe pulmonary hypertension causes blood to flow from right to left through the ductus.
• Clinical signs of Eisenmenger syndrome include cyanotic mucous membranes in the caudal body (vulva or prepuce) with pink gingiva and the absence of a "washing machine" murmur.
• Diagnosis involves radiography and echocardiography.
• Treatment for Eisenmenger syndrome does not include surgical options but may involve managing polycythemia.

Congestive Heart Failure (CHF)

• CHF is caused by reduced myocardial contractility, valvular regurgitation, and marked diastolic dysfunction.
• Clinical signs include cough, exercise intolerance, labored breathing, a crouched posture with elevated chest, ascites, harsh lung sounds/crackles, syncope, restlessness, and potentially a heart murmur or arrhythmia.
• Cats may exhibit paraparesis and cold pelvic limbs if a saddle thrombus occurs.
• Diagnosis involves radiography (heart enlargement, dilated pulmonary veins, interstitial to alveolar lung changes in caudodorsal lung fields) and echocardiography (left atrial +/- left ventricular enlargement causing pulmonary edema, right atrial and ventricular dilation causing ascites, valvular insufficiency, and poor contractility).
• Echocardiography can detect decreased diastolic function with hypertrophic or restrictive cardiomyopathy, systolic anterior motion of the mitral valve, and "smoke" in the left atrium due to swirling of RBCs.
• Acute treatment involves diuretics (furosemide), oxygen, and stress reduction.
• Chronic treatment consists of furosemide, pimobendan, ACE inhibitors, a low-salt diet, and exercise restriction.

Pulmonary Hypertension

• Secondary to mitral valve regurgitation (chronic increased pressure), chronic hypoxia (right to left shunt, chronic respiratory disease), or heartworm.
• Clinical signs of pulmonary hypertension include cough, respiratory distress, exercise intolerance/lethargy, syncope, and ascites.
• Cardiac auscultation may reveal murmurs at the mitral and/or tricuspid valve, split second heart sounds, and pulmonary crackles.
• Diagnosis involves radiography (cardiomegaly, pulmonary artery dilation, tortuous pulmonary arteries, dilated caudal vena cava, pulmonary patterns) and echocardiography (right ventricular hypertrophy, high-velocity tricuspid valve regurgitation, flattening of the interventricular septum, varying right atrial and ventricular dilation).
• Treatment focuses on addressing the underlying disease, oxygen therapy for acute decompensation, pimobendan, and sildenafil.