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Basics ⬇

Basics

Definition

The invasion of the cardiac endocardium, usually the valves, by infectious agents. Usually Gram-positive bacteria, especially staphylococci or streptococci. Occasionally Rickettsia or Bartonella in dogs. Rarely fungi in dogs. Culture-negative cases may be due to Bartonella or fungi (e.g., Aspergillus). Less likely due to Brucella, Coxiella, and Chlamydia.

Pathophysiology

  • Bacteremia develops from various portals of entry; bacteria invade and colonize the heart valves-usually the aortic, occasionally the mitral, and rarely the tricuspid and pulmonic valves.
  • Endocardial ulceration exposes collagen causing platelet aggregation, activation of the coagulation cascade, and formation of vegetations.
  • Vegetations on heart valves are composed of an inner layer of platelets, fibrin, RBCs, and bacteria; a middle layer of bacteria; and an outer layer of fibrin.
  • Valvular insufficiency develops in virtually all patients; aortic insufficiency almost invariably leads to intractable LS-CHF within weeks to several months.
  • CHF is less frequent and latent when only the mitral valve is affected.
  • Vegetative lesions may dislodge causing infarction or metastatic infection to any organ; organs commonly infected include the spleen, kidneys, brain, and skeletal muscles.

Systems Affected

  • Cardiovascular-valvular insufficiency; arrhythmias, myocarditis.
  • CNS-para/tetraparesis; cranial nerve deficits; abnormal mentation.
  • Hemic/Lymphatic/Immune-hypercoagulation; DIC.
  • Musculoskeletal-septic or immune-mediated polyarthropathy; hypertrophic osteopathy; discospondylitis.
  • Renal/Urologic-renal infarction; immune-mediated glomerulonephritis; urinary tract infections.
  • Respiratory-pulmonary edema and/or emboli.

Signalment

Species

Dogs; rarely cats

Breed Predilections

  • Middle-sized to large breeds
  • Breeds predisposed to subaortic stenosis

Mean Age and Range

Most affected dogs are 4–8 years of age; infection can occur at any age.

Predominant Sex

Most studies report male predominance-may be as great as 2:1.

Signs

General Comments

  • Gram-negative bacteremia results in peracute or acute clinical signs; Gram-positive bacteremia results in subacute or chronic clinical signs.
  • Systemic signs are secondary to infarction, infection (inflammation), toxemia, or immune-mediated damage; usually override cardiac signs.

Historical Findings

  • Infectious disease involving the skin, oral, GI, and genital tract (e.g., prostatitis).
  • History of predisposing factors-immunosuppressive drug therapy, aortic stenosis, recent surgery, infected wounds, abscesses, or pyoderma.
  • Common reasons for presentation include lethargy, paresis, fever, anorexia, GI disturbances, and lameness.

Physical Examination Findings

  • Usually diverse and misleading-“the great imitator.”
  • Pyrexia and general malaise.
  • Dyspnea caused by CHF.
  • Arrhythmias (usually ventricular, supraventricular, or heart block).
  • Single or shifting leg lameness.
  • Systolic heart murmur.
  • “To-and-fro” murmur-associated with aortic valve vegetation causing systolic turbulence and diastolic regurgitation.
  • Diastolic murmur component with hyperdynamic femoral pulses are a strong indication of advanced aortic valve endocarditis.

Causes

  • Bacterial infection associated with the oral cavity, bone, prostate, skin, and other sites.
  • Invasive diagnostic or surgical procedures forcing bacteria into the bloodstream.

Risk Factors

  • Congenital subaortic stenosis.
  • Immunosuppression from long-term or high-dose corticosteroids, neoplasia, or cytotoxic drug administration.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Bacteremia of any cause.
  • Polysystemic, immune-mediated disorders.
  • Left-sided CHF caused by dilated cardiomyopathy or congenital subaortic stenosis.

CBC/Biochemistry/Urinalysis

  • Active, severe infection associated with an inflammatory leukogram (i.e., neutrophilia, left shift, and monocytosis)-patients with chronic, relatively inactive, or walled-off infection may have normal or nearly normal leukogram; those with chronic infection may have mature neutrophilia with monocytosis.
  • Nonregenerative anemia.
  • Thrombocytopenia-variable severity.
  • Low-normal or low albumin, low-normal or low glucose, and high SAP/bilirubin activity are inconsistently associated with sepsis (septic triad).
  • Renal azotemia-secondary to renal embolization, pyelonephritis, and/or hypovolemia-induced renal failure.
  • Proteinuria caused by septic embolization, immune-mediated glomerulonephritis, or infarction of the kidneys; hematuria, pyuria, and granular casts associated with pyelonephritis.

Other Laboratory Tests

  • Blood culturing-three samples taken at least 1 hour apart over 24 hours; at least two should yield the same microbe; both aerobic and anaerobic cultures recommended; antibiotic removal systems available for diagnosis of patients given antibiotics.
  • PCR with bacterial 16s primers, in combination with blood culturing, increases the likelihood of identification of bacteria in blood.
  • Culture-negative bacteremia often due to prior antibiotic administration or fastidious microbes, especially Bartonella.
  • Catheter tips-culture.
  • Urine cultures (not a substitute for blood cultures)-easy; often yield positive results; do not necessarily incriminate the urinary tract as the source of infection.
  • Tests for prostate, kidney, and bone infection may be warranted.
  • Positive antinuclear antibody, lupus erythematosus, rheumatoid factor, and Coombs' test results occasionally found-non-specific; tend to confound the diagnosis.
  • Bartonella alpha-Proteobacteria growth medium (BAPGM) and PCR-for Bartonella.

Imaging

Radiographic Findings

Left heart enlargement; rarely, calcification of one or more heart valves.

Echocardiography

Best test-vegetative endocarditis of the aortic valve is easily discerned; mitral valve infection may be difficult to differentiate from myxomatous degeneration. Hyperechoic with chronicity.

Diagnostic Procedures

Joint taps for cytologic examination and culture-cytologic examination usually does not differentiate septic from immune-mediated arthritis; either, usually not septic, can exist with infective endocarditis. Neutrophils are usually non-degenerate regardless of cause.

Electrocardiographic Findings

  • ECG-may be normal; occasionally reflects left heart enlargement; often detects ventricular tachyarrhythmias; occasionally heart block of variable severity or supraventricular tachyarrhythmias.
  • Heart block suggests aortic valve involvement with infection or infarction of the adjacent septum.

Pathologic Findings

  • Cardiomegaly, almost always left sided when present.
  • Vegetative lesions and blood clots on one or more valves.
  • Infection, hemorrhage, and infarction of adjacent myocardium.
  • Renal infarcts are always present and lead to proteinuria and possibly renal failure.
  • Primary or secondary sites of infection, especially kidneys and spleen.
  • Pulmonary hemorrhage or edema.

Treatment ⬆ ⬇

Treatment

Early index of suspicion with aggressive, rapid diagnostic testing, followed by appropriate treatment are imperative for cure. Cure is a reasonable expectation when mitral valve (alone) IE is identified early in its course and treatment is aggressive.

Nursing Care

  • Aggressive fluid therapy-overt or impending CHF limits fluid volumes that can be administered; this problem is virtually insurmountable in patients with concomitant renal failure.
  • Imminent CHF-provide no more than maintenance volumes of fluid; alternate D5W with LRS (or 2.5% dextrose in half-strength LRS); potassium supplementation usually required.

Client Education

Guarded prognosis if only mitral valve involved. The prognosis is grave if the aortic valve is involved.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

Treatment variable-depends on severity of sepsis and presence or absence of CHF.

Antibiotics

  • Backbone of treatment but usually do not eradicate infection before irreversible aortic valve damage occurs; more than minimal damage to the aortic valve is life-threatening because aortic insufficiency tends to be a lethal complication.
  • High-dose IV administration of bactericidal antibiotics is imperative and recommended for as long as feasible (at least 1 week), followed by SC administration for 1 or more weeks.
  • Oral administration-recommended only after at least 4 weeks of injectable therapy and at least 1 week after hematologic and clinical signs of infection and inflammation have disappeared; long-term (>4 months) treatment required to eradicate the infection from the vegetations.
  • Selection determined by both the urgency of septic complications and results of bacterial culture; coagulase-positive staphylococci and streptococci are most often incriminated, so choices can be logically made before culture results are obtained.
  • Coagulase-positive staphylococci-usually resistant to penicillin, hetacillin, amoxicillin, and ampicillin.
  • Streptococci-often resistant to aminoglycosides and fluoroquinolones.
  • Gram-negative bacteria-often sensitive to third-generation cephalosporins, fluoroquinolones, and aminoglycosides.
  • Bartonella-only aminoglycosides appear cidal; can try doxycycline, fluoroquinolone, rifampin, or azithromycin.
  • First-generation cephalosporins-reasonable choice for stable patients until culture results are obtained.
  • Treat life-threatening sepsis immediately with drug combinations. Pending culture results, one of three regimens is recommended: (1) Penicillin, ampicillin, ticarcillin, or a first-generation cephalosporin is combined with an aminoglycoside. Aminoglycosides are not good choices for animals with overt or impending CHF or those with renal azotemia. Gentamicin (2 mg/kg q8h) is recommended for only 5–10 days because of renal toxicity. A fluoroquinolone may be substituted for an aminoglycoside. (2) Clindamycin (2–10 mg/kg IV q8h) plus enrofloxacin (10 mg/kg q24h given diluted 1:1 in sterile water and injected slowly over 15–20 minutes). (3) Advanced-generation cephalosporins or ticarcillin-clavulanic acid (Timentin)-high dosages, but only normal dosages if patient has renal failure.

Treatment of CHF

  • Pimobendan, ACE inhibitor, spironolactone, amlodipine, and furosemide indicated for patients with overt or impending CHF.
  • Oxygen, nitroglycerin, high-dose furosemide (2–8 mg/kg IV), and hydralazine (1–2 mg/kg q12h) for patients with acute, severe pulmonary edema.

Contraindications

  • Avoid antibiotics that cannot penetrate fibrin (e.g., sulfonamides).
  • Corticosteroids.

Other Drugs

  • Anticoagulant therapy-controversial in the prevention of embolization. Heparin not recommended in human medicine as it increases risk of hemorrhage.
  • Aspirin (5–7 mg/kg PO q24h) and/or dalteparin (100 U/kg SC q8h) and/or clopidogrel (2–4 mg/kg PO q24h)-may reduce bacterial dissemination and embolization.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Emergence of antibiotic resistance-relapsing fever and inflammatory leukogram; imperative to adjust treatment on the basis of culture results.
  • Frequent examination and CBC after discharge.
  • Repeat blood cultures 1 week after antibiotics are discontinued or if fever recurs.

Prevention/Avoidance

  • Indwelling catheters-restrict to appropriate indications; aseptic placement; replace within 3–5 days.
  • Administer antibiotics to dog with moderate to severe subaortic stenosis during dentistry or “dirty” procedures.
  • Avoid careless use of corticosteroids.

Possible Complications

  • CHF
  • Renal failure
  • Septic embolization of many tissues and organs
  • Persistent or latent immune-mediated polyarthropathy

Expected Course and Prognosis

  • Best prognosis associated with short history of bacteremia, rapid diagnosis, and aggressive treatment.
  • Mortality relatively higher in animals recently given corticosteroids.
  • Grave prognosis for patients with aortic valve endocarditis.
  • Patients with mitral valve endocarditis can be saved with appropriate treatment.
  • Latent CHF can occur with advance, late diagnosis or inadequate treatment for mitral valve endocarditis.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

Congenital heart defects (usually subaortic stenosis) in some animals.

Synonyms

  • Bacterial endocarditis
  • Infective endocarditis
  • Vegetative endocarditis

Abbreviations

  • ACE = angiotensin converting enzyme
  • APTT = activated partial thromboplastin time
  • CHF = congestive heart failure
  • BAPGM = Bartonella alpha-Proteobacteria growth medium
  • CNS = central nervous system
  • DIC = disseminated intravascular coagulation
  • ECG = electrocardiogram
  • GI = gastrointestinal
  • IE = infective endocarditis
  • PCR = polymerase chain reaction
  • RBC = red blood cell
  • SAP = (serum) alkaline phosphatase

Authors Justin D. Thomason and Clay A. Calvert

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

Client Education Handout Available Online

Suggested Reading

Calvert C, Thomason J. Cardiovascular infections. In: Greene CE, ed. Infectious Diseases of the Dog and Cat. St. Louis: Saunders Elsevier, 2012, pp. 912–936.