Species: Cat

Breed Predilections

Maine coon cats, ragdolls, Sphynx, British and American shorthairs, and Persians.

Mean Age and Range

5–7 years with reported ages of 3 months–17 years. Some breeds of cats including ragdolls and Sphynx may develop the disease at a younger age (average of 2 years of age). HCM is most often a disease of young to middle-aged cats; unexplained murmurs in geriatric cats are more likely associated with hyperthyroidism or hypertension.

Predominant Sex: Male

Historical Findings

• Dyspnea.
• Anorexia.
• Exercise intolerance.
• Vomiting.
• Collapse.
• Sudden death.
• Coughing is uncommon in cats with cardiomyopathy and usually suggests pulmonary disease.

Physical Examination Findings

• Gallop rhythm (S3 or S4).
• Systolic murmur in many animals.
• Apex heartbeat may be exaggerated.
• Muffled heart sounds, lack of chest compliance, and dyspnea characterized by rapid shallow respirations may be associated with pleural effusion.
• Dyspnea and crackles if pulmonary edema is present.
• Weak femoral pulse.
• Acute pelvic limb paralysis with cyanotic pads and nailbeds, cold limbs, and absence of femoral pulse in animals with ATE. Emboli rarely affect thoracic limbs.
• Arrhythmia in some animals.
• May have no clinical signs.

Possible Causes

• Abnormalities of the contractile protein myosin or other sarcomeric proteins (e.g., troponin, myosin binding proteins, tropomyosin).
• Abnormality affecting catecholamine-influenced excitation contraction coupling.
• Abnormal myocardial calcium metabolism.
• Collagen or other intercellular matrix abnormality.
• Growth hormone excess.
• Dynamic left ventricular outflow obstruction may contribute to secondary left ventricular hypertrophy.

Radiography

• Dorsal ventral radiographs often reveal a valentine-appearing heart because of biatrial enlargement and a left ventricle that comes to a point.
• Pulmonary edema, pleural effusion, or both in some animals.
• Radiographs may be normal in asymptomatic cats.
• The different forms of cardiomyopathy cannot be reliably differentiated by radiography.

Echocardiography

• Hypertrophy of the interventricular septum or the left ventricular posterior wall (diastolic wall thickness >6 mm).
• Hypertrophy may be symmetric (affecting IVS and posterior wall) or asymmetric (affecting IVS or posterior wall, but not both).
• Hypertrophy of the papillary muscles.
• Normal or high fractional shortening.
• Normal or reduced left ventricular lumen.
• Left atrial enlargement.
• Systolic anterior motion of the mitral valve (some animals).
• Left ventricular outflow obstruction (some animals). Specialized Doppler studies performed by experienced sonographers often reveal left ventricular relaxation abnormalities (e.g., mitral inflow E:A wave reversal).
• Thrombus in the left atrium (rare).
• Note: There is some overlap between normal cats (especially ketaminized and dehydrated) and cats with mild HCM. Correlate echo findings with physical findings. Presence of left atrial enlargement favors HCM.

Electrocardiography

• Sinus tachycardia (HR >240) is common with heart failure; however, some cats with severe heart failure and hypothermia are bradycardic.
• Atrial and ventricular premature complexes seen more often in cats with cardiomyopathy, but are also occasionally seen in normal cats.
• Atrial fibrillation is seen in some advanced cases.
• A left axis deviation is often seen.
• Cannot differentiate different forms of cardiomyopathy. May be normal.

Systemic Blood Pressure

• Normotensive or hypotensive.
• Evaluate blood pressure in all patients with myocardial hypertrophy to rule out systemic hypertension as the cause of hypertrophy.

Furosemide

• Dosage-1–2 mg/kg PO, IM, IV q8–24h.
• Critically dyspneic animals often require high dosage (4 mg/kg IV). This dose can be repeated in 1 hour if the cat is still severely dyspneic. Indicated to treat pulmonary edema, pleural effusion, and ascites.
• Cats are sensitive to furosemide and prone to dehydration, prerenal azotemia, and hypokalemia.
• Once pulmonary edema resolves, taper to the lowest effective dose.

Pimobendan

• Dosage-0.25–0.3 mg/kg PO q12h.
• Appears to be useful in the management of congestive heart failure (e.g., pulmonary edema or pleural effusion) in cats with HCM, possibly by enhancing diastolic function. Pimobendan is not used in the management of asymptomatic HCM at this time.

ACE Inhibitors

• Dosage-enalapril or benazepril 0.25–0.5 mg/kg PO q24h.
• Indications in cats with HCM not well defined-authors currently use for CHF.

Beta-Blockers

• Dosage-atenolol (6.25–12.5 mg/cat PO q12h).
• Beneficial effects may include slowing of sinus rate, correcting atrial and ventricular arrhythmias, platelet inhibition.
• More effective than diltiazem in controlling dynamic outflow tract obstruction.
• Role in asymptomatic patients unresolved, but authors generally use if dynamic outflow obstruction and hypertrophy present.
• Contraindicated in the presence of CHF.

Diltiazem

• Dosage-7.5–15 mg/cat PO q8h or 10 mg/kg PO q24h (Cardizem CD) or 30 mg/cat q12h (Dilacor XR).
• Beneficial effects may include slower sinus rate, resolution of supraventricular arrhythmias, improved diastolic relaxation, coronary and peripheral vasodilation, platelet inhibition.
• May reduce hypertrophy and left atrial dimensions in some cats.
• Role in asymptomatic patients unresolved.

Aspirin

• Dosage-81 mg/cat q2–3 days if severe atrial enlargement.
• Depresses platelet aggregation, hopefully minimizing the risk of thromboembolism.
• Warn owners that thrombi can still develop despite aspirin administration. Aspirin appears to be not as effective as clopidogrel (1/4 of a 75-mg tablet PO q24h) in the prevention of ATE, at least in cats with a previous embolic episode.

Nitroglycerin Ointment

• Dosage-one-fourth inch/cat topically applied q6–8h or 2.5 mg/24-hour patch.
• Often used in the acute stabilization of cats with severe pulmonary edema or pleural effusion.
• When used intermittently, it may be useful for long-term management of refractory cases.

Spironolactone

• Dosage-1 mg/kg q12–24h.
• Used in conjunction with furosemide in cats with CHF.
• May cause facial pruritis.

Warfarin and Low Molecular Weight Heparin

• Used sometimes in cats at high risk for thromboembolism.
• See chapter, Aortic Thromboembolism.

Clopidogrel

Dosage-18.75 mg/cat/day. Platelet function inhibitor, superior to aspirin in cats with previous ATE.

Beta-Blocker Plus Diltiazem

• Cats that remain tachycardic on a single agent can be treated cautiously with a combination of a beta-blocker and diltiazem.
• Monitor for bradycardia and hypotension.