Cardiomiopatias Felinas

Feline cardiomyopathies are the most common type of heart disease in cats. They consist of specific diseases of the cardiac muscle. In veterinary medicine, at least five different types of cardiomyopathies have been described, including hypertrophic, restrictive, dilated and unclassified cardiomyopathies. More recently, arrhythmogenic right ventricular cardiomyopathy (ARVC) and non-compaction cardiomyopathy have been identified.

History/clinical signs: tachypnea, labored breathing, coughing, paralyzed painful limbs, distended abdomen, syncope.

Physical exam: mucous membrane color and CRT, jugular veins, thoracic auscultation and peripheral pulses.

Diagnostic tests: thoracic radiographs, electrocardiogram, echocardiogram and blood pressure. BNP assays also aid in the diagnosis of hypertrophy and heart failure.

The clinical presentation and treatment of each type of cardiomyopathy can be very diverse, but the clinical outcomes are usually similar.

The most common consequences of feline cardiomyopathies are congestive heart failure, sudden death and aortic thromboembolism (ATE).

Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common cardiac disease in cats. It is characterized by primary concentric hypertrophy.

It is inherited in a simple autosomal dominant pattern with variable penetrance (complete penetrance in Main Coon cats). In humans, more than 400 mutations have been identified. In Main Coon and Ragdoll cats, a mutation in myosin-binding protein C gene was found.

The left ventricular wall, interventricular septum and papillary muscles can present varying degrees of concentric hypertrophy (mild to severe). When the concentric hypertrophy is severe and asymmetric, HCM should always be considered. A hyperechoic endocardium and subendocardium, as well as false tendons, are common findings. Complete end systolic cavity obliteration can be present.

The left atrium may be severely enlarged. The right side is usually not significantly affected.

Systolic anterior motion of the mitral valve (SAM) is a frequent abnormality associated with HCM. It consists of the obstruction of the left ventricular outflow tract (LVOT) by the anterior leaflet of the mitral valve. This phenomenon also causes mitral valve regurgitation secondary to the leaflet movement.

SAM usually results from abnormal papillary muscle orientation, moderate to severe concentric hypertrophy, Venturi and drag effects, and other unexplained factors.

Histology: myocardial fiber disarray, myocardial fibrosis and intramural coronary arteriosclerosis are often found.

Restrictive Cardiomyopathy

Restrictive cardiomyopathy is a group of myocardial conditions that result in abnormal diastolic function and restriction of diastolic filling. Ventricular compliance is impaired by endocardial, subendocardial or myocardial fibrosis.

Severe left and right atrial enlargement is common. The presence of hyperechoic and thickened endocardium is consistent with fibrosis. Multiple false tendons and fibrous plaques can also be found.

The left ventricular internal dimension is often mildly reduced.

Mild concentric hypertrophy, fused papillary muscles and a mild decrease in the systolic function have also been reported.

Histologic findings are usually consistent with endocardial thickening caused by fibrous and granulation tissue.

Pulse wave Doppler of the mitral inflow and tissue Doppler are useful non-invasive modalities for the diagnosis.

Dilated Cardiomyopathy

Dilated cardiomyopathy is a disease of the myocardium that affects its inherent ability to contract. It is characterized by myocardial failure of unknown origin.

Infectious agents (viral, fungal, rickettsial and spirochetal), parasites, toxins, trauma, endocrine diseases and nutritional deficiencies are some of the identified causes of myocardial disease that can lead to myocardial failure.

Taurine deficiency was found to cause dilated cardiomyopathy in cats in the late 80s.

Dilated cardiomyopathy is characterized by moderate-to-severe dilation of all the cardiac chambers, but especially the left side.

The cardiac walls may appear thinner and the papillary muscles may be flattened, though the total myocardial mass is increased. These changes are consistent with significant eccentric hypertrophy.

Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare type of feline cardiomyopathy of uncertain origin, that consists of severe right atrial and ventricular enlargement, with severe right-sided myocardial failure, associated with supraventricular and ventricular arrhythmias. Right ventricular aneurisms are also a common feature. The left side usually does not show significant changes.

Histological findings are consistent with myocardial injury, as well as fibro-fatty or fatty replacement of myocardium.

Right heart failure is the most common clinical presentation.

Unclassified Cardiomyopathy

Unclassified cardiomyopathy includes all those cardiomyopathies that do not fit any of the previous descriptions.

The pathophysiology is not well established, but biatrial enlargement is one of the most common features. The left ventricle may have mild concentric or eccentric hypertrophy. Enlargement of the right ventricle is very variable, but it can be severe.

A mild degree of left ventricular systolic dysfunction as well as atrio-ventricular valvular insufficiencies are also usually present.

Left Ventricular Non-Compaction Cardiomyopathy

Left ventricular non-compaction cardiomyopathy is a very rare myocardial disease that has been well described in people and recently identified in cats.

It is characterized by deep trabeculations in the ventricular wall, which communicate with the main ventricular chamber. The endomyocardium often presents two layers with an increased noncompacted ratio.

The clinical presentation is similar to other cardiomyopathies, including systolic and diastolic dysfunction, aortic thromboembolism and tachyarrhythmias.

Acute Treatment

 Diuretics (furosemide 1–4 mg/kg IV q4–8 h)

 Oxygen

 Positive inotropes (if DCM/RCM: pimobendan 1.25 mg PO BID)

 Thoracocentesis

Chronic Treatment

 Diuretics (furosemide 1–4 mg/kg PO BID–TID, spironolactone 1–4 mg/kg PO BID–TID, hydrochlorothiazide 1-4 mg PO EOD–BID)

 Vasodilators (enalapril 0.5 mg/kg PO SID, benazepril 0.5 mg/kg PO SID)

 Positive inotropes (pimobendan 1.25 mg PO BID, digoxin)

 β-blockers or Ca²⁺ channel blockers (atenolol 6.25–12.5 mg PO SID–BID, diltiazem 7.5 mg PO TID)

Prevention of ATE:

 Platelet aggregation inhibitors (clopidogrel 18.75 mg PO SID, aspirin 20 mg PO q72 h)

 Low molecular weight heparin (enoxaparin 1 mg/kg SQ BID–TID)

 Warfarin

References

1.  Braunwald E, Libby P, Bonow RO, Mann DL, Zipes DP. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. Philadelphia, PA: Saunders Elsevier;2008.

2.  Kittleson MD, Kienle RD. Small Animal Cardiovascular Medicine. St. Louis, Mosby; 1998.

3.  Plumb's Veterinary Drugs, online edition.