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Infectious Disease And Microbiology – Endocarditis (Prosthetic Valve)
Prosthetic valve endocarditis is an infection involving prosthetic heart valves or associated prosthetic material. It is most commonly caused by bacteria, especially Gram-positive organisms, although fungi and, rarely, organisms such as chlamydiae or rickettsiae may also be responsible. This form of endocarditis is a serious complication of valve replacement and can arise either early after surgery or later through bloodstream spread from another infectious source.
The incidence of prosthetic valve infective endocarditis is approximately 0.3–1% per patient-year. The most important risk factors are healthcare-associated infections, chronic intravascular access, and hemodialysis. Additional predisposing factors include the presence of prosthetic valve material itself and any circumstances that increase the likelihood of bloodstream infection.
Prevention includes antibiotic prophylaxis for high-risk patients, particularly before dental procedures that involve manipulation of gingival tissue or disruption of the oral mucosa. Prophylaxis is also considered reasonable for certain respiratory, skin, soft tissue, or muscle procedures in those at highest risk. Recommended prophylactic regimens include a single dose of amoxicillin 2 g or clindamycin 600 mg administered 30–60 minutes before the procedure. Antibiotic prophylaxis is not recommended for gastrointestinal or genitourinary procedures.
The pathophysiology of prosthetic valve endocarditis involves contamination during implantation, later hematogenous seeding of the prosthesis, or contiguous spread of nearby infection. Staphylococci are the most common causes. Early-onset prosthetic valve endocarditis, occurring within 60 days of surgery, is more often due to hospital-acquired pathogens, whereas late-onset infection is caused by organisms more similar to those seen in native valve endocarditis. Early infections are commonly caused by Staphylococcus aureus, coagulase-negative staphylococci, enterococci, Gram-negative bacilli, fungi, and occasionally streptococci. Late infections are more often caused by S. aureus, coagulase-negative staphylococci, streptococci, enterococci, fungi, and Gram-negative bacilli. Culture-negative cases may occur, most often after recent antibiotic exposure or with fastidious organisms such as Bartonella, Coxiella burnetii, Brucella, or Tropheryma whipplei.
The clinical presentation is highly variable. Some patients present with an acute toxic illness and high fever, whereas others have a more indolent subacute course. In any patient with a prosthetic valve and unexplained fever, endocarditis must be strongly considered. Fever is present in more than 70% of cases, and other symptoms may include weakness, chills, sweats, anorexia, weight loss, nausea, and malaise. A careful history should also explore travel, animal exposure, and consumption of unpasteurized dairy products, which may suggest unusual pathogens.
Diagnosis is commonly based on the modified Duke criteria, which combine clinical, microbiologic, and echocardiographic data. Major criteria include persistently positive blood cultures for typical organisms and evidence of endocardial involvement, such as vegetations, abscesses, prosthetic valve dehiscence, or new valvular regurgitation. Minor criteria include predisposition, fever, vascular phenomena, immunologic phenomena, and microbiologic findings that do not meet major criteria.
On physical examination, patients may have a new or changed murmur or signs of congestive heart failure. Because embolic and metastatic complications are common, a full examination should assess for neurologic deficits, splenic involvement, spinal tenderness, joint infection, or other distant sites of disease.
Initial laboratory workup includes complete blood count, electrolytes, renal and liver function tests, inflammatory markers, urinalysis, and multiple blood cultures. At least three sets of blood cultures should be obtained within the first 24 hours before starting antibiotics. The first two sets are positive in most patients. Leukocytosis and elevated ESR or CRP are common. In culture-negative cases, serologic testing for organisms such as Coxiella burnetii and Bartonella should be considered. Blood cultures should be repeated every 24–48 hours until the infection has cleared.
Transesophageal echocardiography is the imaging test of choice because prosthetic valves often create artifact on transthoracic studies and because prosthetic valve infections frequently involve paravalvular complications. TEE has high sensitivity and specificity for detecting vegetations, abscesses, and dehiscence and should be performed as soon as possible when prosthetic valve endocarditis is suspected. Additional imaging of the brain, lungs, abdomen, or spine may be needed if embolic events, abscesses, or mycotic aneurysms are suspected. Electrocardiography is also important to detect baseline or evolving conduction abnormalities, which may indicate abscess extension.
Treatment requires prolonged bactericidal intravenous antibiotic therapy, with regimens tailored to the causative organism and its susceptibilities. For streptococcal infections, treatment typically includes penicillin G or ceftriaxone plus gentamicin, with vancomycin used in selected allergic patients. For enterococci or highly penicillin-resistant streptococci, ampicillin plus gentamicin is commonly used, or vancomycin plus gentamicin if ampicillin cannot be given. Methicillin-susceptible staphylococcal infections are treated with nafcillin plus rifampin for at least six weeks, with gentamicin added for the first two weeks. Methicillin-resistant staphylococcal infections are treated with vancomycin plus rifampin for at least six weeks, again with gentamicin for two weeks. Rifampin is often delayed by a few days because resistance can develop quickly if started too early.
Management requires a multidisciplinary approach involving cardiology, infectious diseases, and cardiovascular surgery. Patients with prosthetic valve endocarditis should be evaluated early for surgery. Valve replacement may be necessary in cases of prosthetic valve dehiscence, perforation, fistula formation, large abscess, severe structural damage, or failure of medical therapy because of highly resistant organisms.
All patients require hospitalization for monitoring, intravenous therapy, and expedited evaluation. They may be discharged once fevers have resolved for more than 24 hours, vital signs are stable, and a safe plan for continued antibiotic treatment and follow-up is in place. During and after therapy, patients should be monitored closely for relapse, treatment complications, and new cardiac dysfunction. At completion of therapy, transthoracic echocardiography is recommended to establish a new baseline for valve and cardiac function.
Patient education is important and should include the importance of good oral hygiene, prevention of future endocarditis associated with dental procedures, and recognition of symptoms of valvular dysfunction. Prognosis depends on several factors. Higher mortality is associated with healthcare-associated infection, congestive heart failure, older age, S. aureus infection, persistent bacteremia, stroke, and intracardiac abscess. In-hospital mortality is substantial. Complications include periprosthetic leak, ring abscess, congestive heart failure, cerebral emboli, stroke, renal infarction, immune complex glomerulonephritis, mycotic aneurysm, meningitis, cerebritis, splenic infarction or abscess, heart block, and pulmonary embolism in right-sided disease.
Prosthetic valve endocarditis is an infection involving prosthetic heart valves or associated prosthetic material. It is most commonly caused by bacteria, especially Gram-positive organisms, although fungi and, rarely, organisms such as chlamydiae or rickettsiae may also be responsible. This form of endocarditis is a serious complication of valve replacement and can arise either early after surgery or later through bloodstream spread from another infectious source.
The incidence of prosthetic valve infective endocarditis is approximately 0.3–1% per patient-year. The most important risk factors are healthcare-associated infections, chronic intravascular access, and hemodialysis. Additional predisposing factors include the presence of prosthetic valve material itself and any circumstances that increase the likelihood of bloodstream infection.
Prevention includes antibiotic prophylaxis for high-risk patients, particularly before dental procedures that involve manipulation of gingival tissue or disruption of the oral mucosa. Prophylaxis is also considered reasonable for certain respiratory, skin, soft tissue, or muscle procedures in those at highest risk. Recommended prophylactic regimens include a single dose of amoxicillin 2 g or clindamycin 600 mg administered 30–60 minutes before the procedure. Antibiotic prophylaxis is not recommended for gastrointestinal or genitourinary procedures.
The pathophysiology of prosthetic valve endocarditis involves contamination during implantation, later hematogenous seeding of the prosthesis, or contiguous spread of nearby infection. Staphylococci are the most common causes. Early-onset prosthetic valve endocarditis, occurring within 60 days of surgery, is more often due to hospital-acquired pathogens, whereas late-onset infection is caused by organisms more similar to those seen in native valve endocarditis. Early infections are commonly caused by Staphylococcus aureus, coagulase-negative staphylococci, enterococci, Gram-negative bacilli, fungi, and occasionally streptococci. Late infections are more often caused by S. aureus, coagulase-negative staphylococci, streptococci, enterococci, fungi, and Gram-negative bacilli. Culture-negative cases may occur, most often after recent antibiotic exposure or with fastidious organisms such as Bartonella, Coxiella burnetii, Brucella, or Tropheryma whipplei.
The clinical presentation is highly variable. Some patients present with an acute toxic illness and high fever, whereas others have a more indolent subacute course. In any patient with a prosthetic valve and unexplained fever, endocarditis must be strongly considered. Fever is present in more than 70% of cases, and other symptoms may include weakness, chills, sweats, anorexia, weight loss, nausea, and malaise. A careful history should also explore travel, animal exposure, and consumption of unpasteurized dairy products, which may suggest unusual pathogens.
Diagnosis is commonly based on the modified Duke criteria, which combine clinical, microbiologic, and echocardiographic data. Major criteria include persistently positive blood cultures for typical organisms and evidence of endocardial involvement, such as vegetations, abscesses, prosthetic valve dehiscence, or new valvular regurgitation. Minor criteria include predisposition, fever, vascular phenomena, immunologic phenomena, and microbiologic findings that do not meet major criteria.
On physical examination, patients may have a new or changed murmur or signs of congestive heart failure. Because embolic and metastatic complications are common, a full examination should assess for neurologic deficits, splenic involvement, spinal tenderness, joint infection, or other distant sites of disease.
Initial laboratory workup includes complete blood count, electrolytes, renal and liver function tests, inflammatory markers, urinalysis, and multiple blood cultures. At least three sets of blood cultures should be obtained within the first 24 hours before starting antibiotics. The first two sets are positive in most patients. Leukocytosis and elevated ESR or CRP are common. In culture-negative cases, serologic testing for organisms such as Coxiella burnetii and Bartonella should be considered. Blood cultures should be repeated every 24–48 hours until the infection has cleared.
Transesophageal echocardiography is the imaging test of choice because prosthetic valves often create artifact on transthoracic studies and because prosthetic valve infections frequently involve paravalvular complications. TEE has high sensitivity and specificity for detecting vegetations, abscesses, and dehiscence and should be performed as soon as possible when prosthetic valve endocarditis is suspected. Additional imaging of the brain, lungs, abdomen, or spine may be needed if embolic events, abscesses, or mycotic aneurysms are suspected. Electrocardiography is also important to detect baseline or evolving conduction abnormalities, which may indicate abscess extension.
Treatment requires prolonged bactericidal intravenous antibiotic therapy, with regimens tailored to the causative organism and its susceptibilities. For streptococcal infections, treatment typically includes penicillin G or ceftriaxone plus gentamicin, with vancomycin used in selected allergic patients. For enterococci or highly penicillin-resistant streptococci, ampicillin plus gentamicin is commonly used, or vancomycin plus gentamicin if ampicillin cannot be given. Methicillin-susceptible staphylococcal infections are treated with nafcillin plus rifampin for at least six weeks, with gentamicin added for the first two weeks. Methicillin-resistant staphylococcal infections are treated with vancomycin plus rifampin for at least six weeks, again with gentamicin for two weeks. Rifampin is often delayed by a few days because resistance can develop quickly if started too early.
Management requires a multidisciplinary approach involving cardiology, infectious diseases, and cardiovascular surgery. Patients with prosthetic valve endocarditis should be evaluated early for surgery. Valve replacement may be necessary in cases of prosthetic valve dehiscence, perforation, fistula formation, large abscess, severe structural damage, or failure of medical therapy because of highly resistant organisms.
All patients require hospitalization for monitoring, intravenous therapy, and expedited evaluation. They may be discharged once fevers have resolved for more than 24 hours, vital signs are stable, and a safe plan for continued antibiotic treatment and follow-up is in place. During and after therapy, patients should be monitored closely for relapse, treatment complications, and new cardiac dysfunction. At completion of therapy, transthoracic echocardiography is recommended to establish a new baseline for valve and cardiac function.
Patient education is important and should include the importance of good oral hygiene, prevention of future endocarditis associated with dental procedures, and recognition of symptoms of valvular dysfunction. Prognosis depends on several factors. Higher mortality is associated with healthcare-associated infection, congestive heart failure, older age, S. aureus infection, persistent bacteremia, stroke, and intracardiac abscess. In-hospital mortality is substantial. Complications include periprosthetic leak, ring abscess, congestive heart failure, cerebral emboli, stroke, renal infarction, immune complex glomerulonephritis, mycotic aneurysm, meningitis, cerebritis, splenic infarction or abscess, heart block, and pulmonary embolism in right-sided disease.
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