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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Infective endocarditis is a bacterial, or rarely fungal, infection of the valvular or mural endocardium
  • A platelet fibrin thrombus attaches to endocardium in response to collagen exposure on a denuded endothelial surface and is colonized during periods of bacteremia. Proliferation of a vegetative mass of fibrin and platelets containing bacteria (or fungi) occurs
  • Microorganisms are most likely to localize on areas of endocardial damage related to valve disease or intra-cardiac shunts
  • The most common site is the mitral valve, followed by the aortic valve
  • The tricuspid valve can be affected with septic jugular vein thrombophlebitis

Pathophysiology!!navigator!!

  • Clinical signs depend on the site and severity of the infection, embolization of vegetations, constant bacteremia, and immune complex disease
  • The vegetative lesion, if large, may obstruct the outflow of blood, and/or lead to permanent valvular damage and valvular incompetence
  • There may also be concurrent myocarditis

Systems Affected!!navigator!!

  • Cardiovascular—primary
  • Respiratory—secondary
  • Nervous—secondary
  • Renal—secondary
  • Hepatobiliary—secondary
  • GI—secondary
  • Musculoskeletal—secondary

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

Uncommon

Signalment!!navigator!!

  • All ages, but horses <3 years constitute the majority
  • No breed or sex predilection

Signs!!navigator!!

General Comments

Usually associated with fever.

Historical Findings

  • Fever
  • Shifting leg lameness
  • Joint or tendon sheath distention
  • Jugular thrombosis

Physical Examination Findings

  • Fever
  • Tachycardia
  • Cardiac murmur; may be absent with right-sided infective endocarditis
  • Other, less common findings—arrhythmias, weight loss, coughing, and CHF

Causes!!navigator!!

Most frequently involves streptococci, Pasteurella/Actinobacillus, and Pseudomonas sp. But a wide range of bacterial species have been implicated, and fungal endocarditis is reported rarely.

Risk Factors!!navigator!!

  • Preexisting endocardial damage
  • Septic jugular vein thrombophlebitis
  • Bacteremia can be associated with dental disease or manipulation but has not been specifically linked with infective endocarditis

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Pericarditis—differentiate echocardiographically
  • Myocarditis—can be concurrent; differentiate echocardiographically
  • Degenerative valve disease—fever and depression are not present
  • Other diseases causing fever of unknown origin (e.g. peritonitis, pleuropneumonia, abscesses, neoplasia)—murmurs and shifting leg lameness usually are not present; differentiate echocardiographically and with clinicopathology and ultrasonography

CBC/Biochemistry/Urinalysis!!navigator!!

  • Often, neutrophilic leukocytosis with elevated SAA hyperfibrinogenemia, hyperglobulinemia, and anemia
  • BUN and creatinine may be increased in horses with infective endocarditis. Azotemia with renal emboli or maybe prerenal in horses with low cardiac output

Other Laboratory Tests!!navigator!!

  • Obtain 3 serial blood cultures at 1 h intervals before treatment with antimicrobials
  • Antimicrobial therapy reduces likelihood of a positive blood culture
  • Increased cardiac troponin I concentrations identify myocardial involvement

Imaging!!navigator!!

Echocardiography

  • Identify oscillating masses associated with the valve apparatus or mural endocardium but small vegetative lesions and lesions in the atria may be difficult to detect with transthoracic echocardiography
  • Determine the number of valve leaflets affected and size of the lesions
  • Doppler examination documents valvular regurgitation

Thoracic Radiography

  • Pulmonary edema indicates CHF
  • Pneumonia may be present with right-sided endocarditis

Other Diagnostic Procedures!!navigator!!

ECG identifies concurrent arrhythmias.

Pathologic Findings!!navigator!!

  • Focal or diffuse thickening or distortion of valve leaflets with vegetative masses on the leaflet, chordae tendineae, or mural endocardium
  • Ruptured chordae tendineae
  • Jet lesions usually are detected in the preceding chamber
  • Enlargement and thinning of the walls of the chambers receiving the regurgitation
  • Myocardial inflammatory cell infiltrate, necrosis, and fibrosis detected histopathologically
  • Infarcts and abscesses secondary to septic embolization particularly in the lung, kidneys, spleen, myocardium, and brain

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

The goals of treatment are sterilization of the vegetations and provision of cardiovascular support.

Appropriate Health Care!!navigator!!

  • Hospitalize horses with infective endocarditis, and treat with systemic, bactericidal, broad-spectrum antimicrobials that are initially empirical and subsequently based on results of blood culture and sensitivity and clopidogrel for its antiplatelet activity
  • Horses with moderate to severe mitral or aortic regurgitation may benefit from long-term vasodilator therapy
  • Treat horses with severe mitral, aortic, or tricuspid regurgitation and CHF with positive inotropic drugs, vasodilators, and diuretics
  • Closely monitor response to therapy with clinical, clinicopathologic, and echocardiographic reevaluations

Nursing Care!!navigator!!

N/A

Activity!!navigator!!

  • Stall rest and hand-walking only while being treated for infective endocarditis
  • Once a bacteriologic cure is achieved, rest with small paddock turnout is appropriate
  • Ability of the horse to return to work successfully depends on severity of the residual valvular damage
  • Horses with significant ventricular arrhythmias or pulmonary artery dilatation are no longer safe to ride

Client Education!!navigator!!

  • Monitor the horse's temperature daily, preferably during the late afternoon or evening, during treatment of infective endocarditis and after discontinuation of antimicrobials
  • Regularly monitor cardiac rhythm; any irregularities other than second-degree atrioventricular block should prompt ECG
  • Carefully monitor for exercise intolerance, respiratory distress, prolonged recovery after exercise, increased resting respiratory or heart rate, cough, or edema; if detected, see Patient Monitoring.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Infective Endocarditis

  • To cure endocarditis requires sterilization of the vegetation
  • Bactericidal antimicrobials can be administered for 4–6 weeks
  • Empirically, until blood culture and sensitivity results are available, penicillin and gentamicin are a good combination. Enrofloxacin is likely to penetrate vegetations and rifampin (rifampicin) may be added to improve penetration of the antimicrobial into the lesion
  • Administer aspirin or clopidogrel to decrease platelet adhesiveness
  • With life-threatening ventricular arrhythmias, institute appropriate antiarrhythmic drugs

Valvular Insufficiency

Treat affected horses in CHF with furosemide, vasodilators such as benazepril, quinapril, or the inodilator pimobendan.

Precautions!!navigator!!

  • Evaluate creatinine and BUN before starting aminoglycoside antimicrobials and use therapeutic drug monitoring to individualize dosage regimens
  • ACE inhibitors can cause hypotension; thus, do not give as a large dose without time to accommodate to this treatment

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Assess CBC and in particular serum creatinine and fibrinogen concentrations
  • Frequently monitor lesions echocardiographically during treatment with antimicrobials to assess the efficacy of treatment
  • Once antimicrobials have been discontinued, monitor lesions echocardiographically 2 and 4 weeks later and periodically thereafter, depending on the valve affected and the severity of the valvular regurgitation that has developed
  • With severe valvular insufficiency, echocardiographic reevaluations are recommended at 3 month intervals

Prevention/Avoidance!!navigator!!

Institute aggressive treatment of septic jugular vein thrombophlebitis to minimize seeding of the tricuspid valve from septic emboli associated with the infected jugular vein.

Possible Complications!!navigator!!

  • Immune-mediated synovitis or tenosynovitis
  • Right-sided infective endocarditis—pulmonary thromboembolism, pulmonary abscess, and pneumonia
  • Left-sided infective endocarditis—hepatic, splenic, and renal abscess; myocardial and cerebral infarction

Expected Course and Prognosis!!navigator!!

  • Prognosis for horses is primarily determined by the valve(s) affected and the severity of valvular damage that develops, and is also likely to be influenced by the organism(s) involved and the response to antimicrobial treatment
  • Prognosis for horses with right-sided infective endocarditis is guarded and for left-sided infective endocarditis is grave
  • Achieving bacteriologic cure can be difficult
  • Even when bacteriologic cure is achieved, continued damage to the affected valve occurs. This usually results in worsening of the valvular regurgitation. These horses may develop clinical signs associated with the worsening valvular insufficiency that shortens both useful performance life and life expectancy

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Septic jugular vein thrombophlebitis
  • Preexisting valve damage
  • Congenital cardiac disease

Age-Related Factors!!navigator!!

Infective endocarditis is more frequent in horses <3 years of age.

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

  • Pregnant mares are at risk for development of placentitis, and the fetus may become septic
  • Treating pregnant mares with IV broad-spectrum bactericidal antimicrobials is important. Base the antimicrobial therapy on blood culture and sensitivity, if available, and choose antimicrobials that are safe for the developing fetus
  • The volume expansion of late pregnancy places an additional load on the already volume-loaded heart and may precipitate CHF in mares with severe valvular insufficiency
  • In pregnant mares with CHF, treat for the underlying cardiac disease with positive inotropic drugs and diuretics. ACE inhibitors are contraindicated because of potential adverse effects on the fetus

Synonyms!!navigator!!

  • Vegetative endocarditis
  • Infective endocarditis

Abbreviations!!navigator!!

Suggested Reading ⬆ ⬇

Buergelt CD, Cooley AJ, Hines SA, Pipers FS. Endocarditis in 6 horses. Vet Pathol 1985;22:333–337.

Kasari TR, Roussel AJ. Bacterial endocarditis. Part I. Pathophysiologic, diagnostic and therapeutic considerations. Compend Contin Educ Pract Vet 1989;11:655–671.

Marr CM. Cardiovascular Infections. In Sellon DC, Long MT, eds. Equine Infectious Disease, 2e. St. Louis, MO: Elsevier, 2014:21–41.

Maxson ADM, Reef VB. Bacterial endocarditis in horses: a review of 10 cases (1984–1995). Equine Vet J 1997;29:394–399.

Porter SR, Saegerman C, van Galen G, et al. Vegetative endocarditis in equids (1994-2006). J Vet Intern Med 2008;22:1411–1416.

Author(s) ⬆

Author: Celia M. Marr

Consulting Editor: Celia M. Marr and Virginia B. Reef

Acknowledgment: The author acknowledges the prior contribution of Virginia B. Reef.