Definition

• Dilated cardiomyopathy is a disease of the heart muscle characterized by systolic myocardial failure and a dilated, volume overloaded heart that leads to signs of congestive heart failure or low cardiac output.
• Before 1987, dilated cardiomyopathy was the second most commonly diagnosed heart disease in cats. Most cats had a secondary dilated cardiomyopathy as a result of taurine deficiency. Primary idiopathic dilated cardiomyopathy is now an uncommon cause of heart disease in cats.

Pathophysiology

Histopathologically, the myocardium of cats with idiopathic DCM has evidence of myocytolysis, fibrosis, myofibril fragmentation, and vacuolization. Gross examination reveals global eccentric enlargement of all four cardiac chambers. These anatomic changes are associated with progressive myocardial systolic failure, decreased contractility, decreased compliance and secondary mitral valve regurgitation due to mitral valve annular dilation. These changes are typically identified by echocardiography. Eventually, the chronic myocardial dysfunction leads to congestive heart failure and clinical signs.

Systems Affected

• Cardiovascular-DCM is a primary myocardial disease and primarily affects the heart and its ability to maintain an adequate cardiac output to maintain the body's needs.
• Musculoskeletal-cats with DCM can present with aortic thromboembolism, which causes acute paraparesis or monoparesis.
• Renal/Urologic-cats with DCM and congestive heart failure often have poor renal perfusion and commonly have prerenal azotemia.
• Respiratory-cats usually present with tachypnea or dyspnea due to congestive heart failure with DCM. These cats can develop both pulmonary edema and pleural effusion.

Genetics

Because of the human experience with DCM, it is likely that feline DCM has a genetic mutation, either inherited or de novo, as the cause of their disease. No definitive mutation has been identified in the cat to date. Additionally, a quantitative genetic evaluation of a large cattery suggested an inherited factor in the development of DCM.

Incidence/Prevalence

Idiopathic feline DCM is relatively uncommon now that taurine is adequately supplemented in cat foods. A retrospective survey 106 cats with feline myocardial disease from 1994 to 2001 from Europe revealed that DCM was diagnosed in approximately 10% of the cases in this series. In the author's experience, the prevalence of feline idiopathic DCM may be less than 10%.

Signalment

Signs

Causes

The underlying etiology of idiopathic dilated cardiomyopathy remains unknown, although a genetic predisposition has been identified in some families of cats. Taurine deficiency was a common cause of secondary myocardial failure before 1987.

Differential Diagnosis

• Taurine deficiency dilated cardiomyopathy. Because primary idiopathic dilated cardiomyopathy and taurine deficiency have similar clinical presentations, cats with myocardial failure should be assumed to have taurine deficiency until shown to be unresponsive to taurine.
• Myocardial failure secondary to long-standing congenital or acquired left ventricular volume overload diseases.
• End-staged remodeled hypertrophic cardiomyopathy may manifest with a dilated hypocontractile heart.
• Arrhythmogenic right ventricular cardiomyopathy.

CBC/Biochemistry/Urinalysis

Many cats will have prerenal azotemia related to low cardiac output.

Other Laboratory Tests

• Ensure that thyroid concentrations are normal.
• Plasma taurine concentrations less than 40 nmol/L or whole blood taurine concentrations less than 250 nmol/L are subnormal and suggestive of taurine-deficiency dilated cardiomyopathy. Taurine assays are performed at a limited number of institutions and require special handling.
• Cardiac biomarkers such as plasma amine terminal B-type natriuretic peptide (NT-proBNP) and cardiac troponin I (cTnI) concentrations would be elevated in a cat with congestive heart failure due to idiopathic dilated cardiomyopathy.

Imaging

Diagnostic Procedures

Pathologic Findings

• Heart:body ratio is increased.
• All four cardiac chambers are dilated. Ventricular walls are thin and left ventricular lumen is enlarged.
• Valve anatomy is normal.
• Histopathology shows myocytolysis and myocardial fibrosis.

Appropriate Health Care

These cats usually present in congestive heart failure and should be treated as inpatients, typically in an intensive care setting until more stable.

Nursing Care

• Thoracocentesis is often utilized for both therapeutic and diagnostic purposes.
• Supplemental oxygen therapy is beneficial for cats in congestive heart failure to decrease the work of breathing.
• If hypothermic, cautious external heat (incubator or heating water pad) is recommended.

Activity

Indoors only after hospital discharge to reduce stress. Let cat dictate its own activity.

Diet

These cats typically are anorexic, thus tempting their appetite with many types of food may be necessary. Eventually, a low-sodium diet is recommended.

Client Education

Some cats will need chronic intermittent thoracocentesis to manage large amount pleural effusion despite medical therapy.

Drug(s) Of Choice

• Furosemide is recommended to manage pulmonary edema and pleural effusion. Recommended dose range is 1–4 mg/kg q8–12h. Initially, administer parenterally then switch to oral. Chronically the lowest effective dose of furosemide is recommended.
• Pimobendan, an inodilator, is also recommended to strengthen contractility and provide some vasodilation. Recommended dose range is 0.1–0.3 mg/kg PO q12h. Although pimobendam is not currently licensed for use in cats, several recent publications have demonstrated its safety in cats and possibly a beneficial effect, albeit in retrospective studies. One study in cats with non-taurine responsive dilated cardiomyopathy who were treated with pimobendan had a median survival time that was four times longer than the cats not treated with pimobendan (49 vs. 12 days).
• Taurine supplementation is recommended initially in all cats with dilated cardiomyopathy at 250 mg PO q12h until it is demonstrated that the patient is unresponsive to taurine or is not taurine deficient based on diagnostic testing.
• Nitroglycerin (2% ointment) one-fourth to one-half inch applied topically can be used in conjunction with diuretics in the acute management of severe congestive heart failure to further reduce preload. Nitroglycerin will lower the dose of furosemide and is particularly useful in patients with hypothermia or dehydration.
• Enalapril or benazepril, at a dose of 0.25–0.5 mg/kg PO q24h is recommended to reduce afterload and preload as soon as the cat is able to take oral medications and is clinically stable. Use with caution and possibly avoid if creatinine >2.5 mg/dl.
• Digoxin is optionally recommended to strengthen contractility and for its positive neurohumoral effects at a dose of 0.03 mg/cat (one-fourth of a 0.125-mg tablet) or 0.01 mg/kg PO q48h. Digoxin can be given concurrently with pimobendan. However, digoxin is often omitted when pimobendan is given because of the difficulties in giving a cat several pills and digoxin's side-effect profile.
• Dobutamine at extremely low dosages can be given to a patient with severe signs of congestive heart failure and low cardiac output that cannot take oral medications. Dose varies 0.25–5 µg/kg/minute IV CRI. ECG monitoring is recommended.
• Because thromboembolic disease is a concern, an antithrombotic agent is also recommended. Clopidogrel given at a dose of 18.75 mg (one-fourth of a 75-mg tablet) PO q24h is generally the author's preferred antithrombotic agent. Other options include aspirin 81 mg PO q72h (with food) or low molecular weight heparin (e.g., daltaperin 100–150 units/kg SC q8–24h or enoxaparin 1 mg/kg SC q12–24h).
• Antiarrhythmic drugs may also be needed to control supraventricular or ventricular arrhythmias. If hemodynamically significant supraventricular tachycardia or rapid atrial fibrillation is present, diltiazem is recommended. Usually, diltiazem is given orally in either a non-sustained-release formulation (7.5 mg/cat PO q8h) or a sustained-release oral formulation (Cardizem CD at 10 mg/kg PO q24h or Dilacor 30 mg/cat [or 1/2 of an inner 60-mg tablet] PO q12h). Diltiazem is also available in an injectable formulation for urgent control of a supraventricular arrhythmia in a cat that cannot take oral medications (0.05–0.1 mg/kg slow IV, repeated PRN up to 0.25 mg/kg). If rapid and sustained ventricular tachycardia, lidocaine slow IV 0.2–0.5 mg/kg (repeat once or twice max) or sotalol PO 2 mg/kg q12h is recommended.
• Beta-blockers, such as atenolol, may be useful in the chronic management of both supraventricular and ventricular arrhythmias. Beta-blockers are used in the long-term management of dilated cardiomyopathy in humans because of their positive myocardial effects and survival benefit. Clinical experience is limited in feline dilated cardiomyopathy and they must be used cautiously as they acutely decrease contractility and could worsen congestive heart failure. Recommended dose ranges from 3.125 to 6.25 mg PO q12–24h. Start low and titrate up based on heart rate and clinical signs.

Precautions

• Unless needed for acute cardiac rhythm control, drugs such as calcium channel blockers (diltiazem) or -adrenergic blockers may reduce contractility and lower cardiac output. Use cautiously.
• Overzealous diuretic and vasodilation therapy may cause azotemia and electrolyte disturbances.
• Digoxin should not be used if renal insufficiency is documented or suspected.
• Enalapril or benazepril should be used with caution and possibly withheld if serum creatinine is >2.5 mg/dL.
• Dobutamine may cause seizures and cardiac tachyarrhythmias.

Patient Monitoring

• Repeat examination with ideally a blood pressure, diagnostic imaging (either a thoracic radiograph or focused thoracic ultrasound for fluid assessment) and chemistry panel within 1 week to determine response of therapy.
• Home resting respiratory rate monitoring is helpful to determine need for diuretic dose adjustment or thoracocentesis.
• Periodically monitor electrolyte and renal parameters. Periodically monitoring of congestive heart failure fluid accumulation with diagnostic imaging.
• If using digoxin, serum blood concentrations should be measured approximately 10–14 days after initiating therapy. Therapeutic range is 0.5–1.5 ng/dL 8–12 hours post-pill.
• Repeat diagnostic echocardiogram in 2–3 months after initiating taurine supplementation to determine echocardiographic response to therapy. Although echocardiographic response may take 2–3 months to assess, one should see dramatic clinical response within 2 weeks of initiating taurine therapy if cat has taurine responsive dilated cardiomyopathy.

Prevention/Avoidance

Ensure that cats eat a high-protein diet with sufficient dietary taurine. No vegetarian diets.

Possible Complications

Thromboembolism is the most feared complication of any feline myocardial disease.

Expected Course and Prognosis

• These cats have a poor prognosis despite intensive therapy. If cat is not taurine-responsive, survival is usually weeks to months.
• Congestive heart failure can be medically refractory and recurrent despite appropriate medical therapy.
• Repeated thoracocentesis is not uncommon.

Associated Conditions

Congestive heart failure, thromboembolism, pleural effusion, cardiac arrhythmias.

Synonyms

Cardiomyopathy

See Also

• Aortic Thromboembolism
• Congestive Heart Failure-Left-Sided
• Congestive Heart Failure-Right-Sided

Abbreviations

• CHF = congestive heart failure
• DCM = dilated cardiomyopathy