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Basics ⬇

Basics

Overview

  • Endomyocarditis-acute cardiopulmonary disease that typically develops following a stressful event; characterized by interstitial pneumonia and endomyocardial inflammation; pneumonia is usually severe and commonly causes death; one report recorded the incidence of endomyocarditis at post-mortem to be equivalent to that of hypertrophic cardiomyopathy.
  • Endocardial fibroelastosis-congenital heart disease in which severe fibrous endocardial thickening leads to heart failure secondary to diastolic and systolic failure.
  • Excessive moderator bands (EMBs)-a rare and unique pathologic disease. Moderator bands are normal muscular bands in the right ventricle, but they can sometimes occur in the left ventricle.

Signalment

  • Cats.
  • Endomyocarditis-predominantly males (62%) age 1–4 years.
  • Endocardial fibroelastosis-early development of biventricular or left heart failure, usually prior to 6 months of age.
  • EMBs-can be seen in any age cat.

Signs

Historical Findings

Endomyocarditis

  • Dyspnea following a stressful event in a young, healthy cat.
  • Respiratory signs usually occur 5–21 days after the stressor.
  • In one report, 73% of cases presented between August and September.

Endocardial Fibroelastosis and EMBs

  • Lethargy, weakness, collapse, syncope
  • Poor appetite and weight loss
  • Dyspnea
  • Tachypnea
  • Cyanosis
  • Abdominal distention
  • Paresis or paralysis; signs of thromboembolic disease.

Physical Examination Findings

Endomyocarditis

  • Severe dyspnea
  • Occasional crackles
  • May be murmur or gallop; murmur may vary in intensity
  • May be evidence of thromboembolic disease
  • Typically no significant abnormalities prior to the stressful event.

Endocardial Fibroelastosis and EMB

  • Gallop
  • Systolic murmur, possible mitral regurgitation
  • Dyspnea and increased lung sounds or crackles
  • Paresis or paralysis with weak or absent femoral pulses.
  • Arrhythmias possible.

Causes & Risk Factors

  • Cause unknown for all three diseases.
  • Risk factors for endomyocarditis include stressful incidents such as anesthesia (commonly associated with neutering or declawing), vaccination, relocation, or bathing.
  • Endocardial fibroelastosis may be familial in Burmese and Siamese cats.
  • The appearance of EMBs in a young cat would suggest a congenital malformation.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

Other Causes of Cardiac Disease

Hypertrophic cardiomyopathy, unclassified cardiomyopathy, restrictive cardiomyopathy, dilated cardiomyopathy, congenital heart malformations.

Other Causes of Dyspnea

  • Other forms of cardiac disease, hypertrophic cardiomyopathy, unclassified cardiomyopathy, restrictive cardiomyopathy, dilated cardiomyopathy, congenital malformations
  • Primary respiratory disease
  • Pleural space disease
  • Mediastinal disorders, infection, trauma, neoplasia
  • Hemoglobin disorders, anemia, methemoglobinemia, causes of central cyanosis.

Other Causes of Collapse, Weakness, or Syncope

  • Arrhythmias
  • Neurologic or musculoskeletal disease
  • Metabolic disease or electrolyte disorders
  • Other forms of paresis or paralysis
  • Arterial thromboembolism secondary to any form of cardiac disease or neoplasia
  • Neurologic or musculoskeletal disease
  • Neoplasia.

CBC/Biochemistry/Urinalysis

Not diagnostic

Other Laboratory Tests

N/A

Imaging

Thoracic Radiographic Findings for All Three Diseases

  • Cardiomegaly
  • Interstitial or alveolar infiltrates or pleural effusion if congestion has developed.

Echocardiographic Findings

Endomyocarditis

  • Normal to mildly large left atrium
  • Left ventricular wall thickness can be normal to mildly thick (0.6–0.7 cm)
  • Hyperechoic endomyocardium reported-incidence seems to vary and is subjective; in one report it was as high as 86%.

Endocardial Fibroelastosis

  • Limited data available
  • Reduced left ventricular function and enlarged left atrium.

Excessive Moderator Bands

  • Many findings can overlap restrictive cardiomyopathy. A network of false tendons can sometimes be imaged with two-dimensional echocardiography.

Diagnostic Procedures

Electrocardiographic Findings

  • Endomyocarditis-sinus tachycardia common; ventricular premature complexes, atrial premature complexes, bundle branch block, and complete AV block reported.
  • Endocardial fibroelastosis-evidence for left-sided enlargement; sinus rhythm typically present, but various arrhythmias possible.
  • EMBs-various electrocardiographic findings have been reported: AV block, sinus bradycardia, right bundle branch block, and left axis deviation.

Pathologic Findings

Endomyocarditis

  • Interstitial pneumonia.
  • Left heart enlargement and opacity of the left ventricular endomyocardium with foci of hemorrhage; fibroplasia of the endocardium is striking.
  • Varying degrees of endomyocardial inflammation with infiltrates of neutrophils, lymphocytes, plasma cells, histiocytes, and macrophages seen histologically.

Endocardial Fibroelastosis

  • Left ventricular and atrial dilation with severe diffuse white opaque thickening of the endocardium.
  • Diffuse hypocellular, fibroelastic thickening of the endomyocardium; prominent endomyocardial edema with dilation of lymphatics.

Excessive Moderator Bands

  • Changes typically include an irregular left ventricular endocardial contour with a rounded apex and numerous irregular left ventricular false tendons. Heart weights can be greater than normal. The moderator bands are composed of central Purkinje fibers and collagen.

Treatment ⬆ ⬇

Treatment

Endomyocarditis

  • No single therapy protocol to date.
  • Small percentage of cats have survived; these cats are not on long-term therapy.
  • Supportive care with oxygen and possibly ventilation.

Endocardial Fibroelastosis and Embs

  • Oxygen therapy via cage delivery is least stressful.
  • Thoracocentesis if pleural effusion.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

Endomyocarditis

Steroids, furosemide, and vasodilators have been tried, but efficacy is still unknown.

Endocardial Fibroelastosis and EMB Acute CHF

  • Parenteral administration of furosemide, 0.5–1 mg/kg IV or IM, q1–6h.
  • Dermal application of 2% nitroglycerin ointment, one-eighth to one-fourth inch q4–6h.
  • Arrhythmias may resolve with stabilization. If there is rapid atrial fibrillation (heart rate >200), a calcium channel blocker or beta-blocker can be given to help control the ventricular response. If there is dilated cardiomyopathy, digoxin may be a better choice for controlling the atrial fibrillation rate. For other supraventricular arrhythmias and ventricular arrhythmias, waiting for a response to heart failure therapy may be wise before starting antiarrhythmic therapy.
  • Intractable edema-nitroprusside, 1–5 µg/kg/minute, may be helpful.

Chronic CHF

  • Treat as other CHF, with furosemide and enalapril.
  • Digoxin can be added when patient is stable and eating.

Contraindications/Possible Interactions

N/A

Follow-Up ⬆ ⬇

Follow-Up

Expected Course and Prognosis

  • Endomyocarditis-poor, although some animals survive; animals that survive respiratory phase may progress to left ventricular endocardial fibrosis.
  • Endocardial fibroelastosis and EMBs-medical treatment of CHF may prolong life, but recovery is unlikely.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

  • Aortic thromboembolism.
  • Relationship possible between endomyocarditis and left ventricular endocardial fibrosis.

Abbreviations

  • AV = atrioventricular
  • CHF = congestive heart failure
  • EMB = excessive moderator band

Author Carl D. Sammarco

Consulting Editors Larry P. Tilley and Francis W.K. Smith, Jr.

Suggested Reading

Bossbaly MB, Stalis I, Knight D, Van Winkle T. Feline endomyocarditis: A clinical/pathological study of 44 cases. Proceedings of the 12th ACVIM Forum, 1994, p. 975.

Liu S, Tilley LP. Excessive moderator bands in the left ventricle of 21 cats. JAVMA 1982, 180:1215–1219.

Stalis IH, Bossbaly MJ, Van Winkle TJ. Feline endomyocarditis and left ventricular endocardial fibrosis. Vet Pathol 1995, 32(2):122–126.

Wray JD, Gajanayake I, Smith SH. Congestive heart failure associated with a large transverse left ventricular moderator band in a cat. J Feline Med Surg 2007, 9:56–60.