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2024/25 Test Bank for Human Anatomy & Physiology, 12th Edition by Marieb & Hoehn. 978-1292421810|| Complete Guide|| Graded A+
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TEST BANK Human Anatomy & Physiology, (12TH) Global Edition By Elaine Marieb.
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STATE OF THE ARTSurgical Management of
Mitral Valve Infective Endocarditis
Charles F. Evans, MD, and James S. Gammie, MD
Active mitral valve infective endocarditis is a challenging clinical problem with a high rate of
mortality. Surgery is currently performed in more than 40% of patients, and selecting those
patients who will benefit from surgical intervention and performing a technically sound operation
at the proper time are keys to optimizing outcomes. Moderate-to-severe and severe mitral
regurgitation, large, mobile vegetations, paravalvular abscess, embolic events, failure of antibiotic
therapy, and infection with a fungal organism are indications for prompt operation. The use of
computed tomography imaging is important to determine whether there are noncardiac sources
of infection, and transesophageal echocardiography is essential to delineate valvular dysfunction,
identify paravalvular abscesses, rule out involvement of other valves, and plan operative therapy.
In most cases, surgery should not be delayed because of cerebrovascular emboli. Mitral valve
repair is favored over replacement whenever possible, is associated with superior short- and
long-term outcomes, and should be possible in most cases. Operative mortality is ⬍10% and
5-year survival is ⬎80%.
Semin Thoracic Surg 23:232-240 © 2011 Elsevier Inc. All rights reserved.
Keywords: endocarditis, mitral valve, surgery
Active mitral valve infective endocarditis (IE) is a and thus individual surgeon experience is lim-
challenging clinical problem. The in-hospital mor- ited.6 Identifying patients who will benefit from
tality from left-sided IE ranges from 26%1 to 30%2 surgery, operating at the correct time, and per-
and has not decreased in the past 40 years3 despite forming a technically sound operation are criti-
progress in medical and surgical treatment. The in- cally important to decrease the mortality and mor-
cidence of IE has also remained constant over time bidity of mitral valve IE.
and affects 5-15 per 100,000 people per year.4 Al-
though risk factors such as rheumatic heart disease
have become less prevalent, intravenous drug use, PATHOPHYSIOLOGY
degenerative valvular disease, and health care-asso- In left-sided native valve IE, the mitral valve is
ciated infection are more common and may account involved in 50%-56% of cases, the aortic valve in
for the unchanged prevalence of mitral valve IE. In 35%-49% of cases,2,5 and both valves in 15% of
North America, health care exposure, such as intra- cases.1 In contemporary series of left-sided IE, Staph-
venous therapy, hemodailysis, hospitalization, or ylococcus aureus and Streptococcal species are the
residence in a long-term care facility, accounts for most common causative bacteria.5 The vegetation of
38% of all IE.5 In a contemporary prospective inter- IE typically forms on the atrial side of the mitral valve
national cohort study, 46.6% of patients with IE un- beyond areas of high shear stress in areas of low
derwent operative intervention.5 Operations for mi- shear stress7 and is composed of bacteria, platelets,
tral valve IE are uncommon; they comprise only and fibrin.4 Factors that favor the development of an
5.8% of mitral valve operations in North America, endocarditic lesion include bacteremia, endocardial
damage, unfavorable hemodynamics, virulent bacte-
ria, and defects in host defense.7
Division of Cardiac Surgery, Department of Surgery, Uni- The pathogenesis of vegetation formation in endo-
versity of Maryland School of Medicine, Baltimore, Mary-
carditis depends on the interaction of host and bac-
land.
terial factors. On the host side, endothelial damage
Address reprint requests to James S. Gammie, MD, Divi- (in rheumatic or degenerative disease) and dysfunc-
sion of Cardiac Surgery, Department of Surgery, N4W94,
University of Maryland Medical Center, 22 South Greene
tion leads to exposure of the extracellular matrix,
Street, Baltimore, MD 21201. E-mail: jgammie@smail. release of cytokines, expression of adhesion mole-
umaryland.edu cules, and increased tissue factor activity.8 Bacteria
232 1043-0679/$-see front matter © 2011 Elsevier Inc. All rights reserved.
doi:10.1053/j.semtcvs.2011.07.005
, SURGICAL MANAGEMENT OF MITRAL VALVE IE
Table 1. Modified Duke Criteria
Major criteria ● Two separate positive blood cultures with organisms typical for IE: Viridans
Streptococci, Streptococcus bovis, HACEK group, Staphylococcus aureus,
community-acquired enterococci
● Echocardiographic evidence of endocardial involvement: vegetation, abscess, new
partial dehiscence of a prosthetic valve, new valvular regurgitation
Minor criteria ● Predisposing heart condition or intravenous drug use
● Temperature ⬎38.0°C
● Vascular phenomena: arterial emboli, pulmonary infarcts, mycotic aneurysm,
intracranial hemorrhage, conjunctival hemorrhage, Janeway lesions
● Immunologic phenomena: glomerulonephritis, Osler’s nodes, Roth’s spots, rheumatoid
factor
● Microbiologic evidence that does not meet a major criterion
HACEK, Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella; IE, infective endocarditis.
express microbial surface component reacting with available evidence is retrospective and observational;
adhesive matrix molecules, or MSCRAMMs, that thus, it is subject to selection bias and survivor selec-
bind to the extracellular matrix.4 Endothelial dam- tion treatment bias.11
age is not a prerequisite for bacterial adhesion. S Numerous studies have reported both short-12-14
aureus has fibrinogen- and fibronectin-binding pro- and long-term15-17 survival benefit of operation for
teins that bind directly to fibrinogen and fibronectin patients with active IE. In one study in which the
on the surface of otherwise undamaged endothelial authors used propensity matching to compare 218
cells.9 Bacteria are also able to bind and activate matched patients from a cohort of 513, 230 of whom
platelets.8 underwent operation and 283 of whom received
In either case, bacterial adhesion to the valve is the medical therapy alone, operative intervention was
primary event that subsequently generates an in- associated with significantly lower 6-month mortal-
flammatory response.4 Monocytes respond to cyto- ity (15% vs 28%, hazard ratio ⫽ 0.45), with the
kines and contribute to ulceration, tissue destruction greatest survival benefit found in patients with mod-
and fibrotic scarring of the valve.9 Tissue factor acti- erate-to-severe congestive heart failure (6-month mor-
vates the coagulation cascade and attracts platelets, tality ⫽ 14% vs 51%, hazard ratio ⫽ 0.22).12 In another
which are integral components of the vegetation.8 As study in which the authors used propensity match-
the vegetation grows, bacteria continue to bind and ing to compare 720 patients who received early sur-
proliferate within it where they are relatively pro- gery with 832 patients who received medical therapy
tected from host defenses. alone, early surgery was associated with significantly
lower in-hospital mortality (unadjusted mortality
DIAGNOSIS 12.1% vs 20.7%). The mortality benefit of surgery
The diagnosis of IE is based on the Duke Crite- was demonstrated in multivariable and propensity-
ria.10 The diagnosis of IE depends on the presence of matching analyses, with a demonstrated absolute
2 major, 1 major and 3 minor, or 5 minor criteria mortality risk reduction of 5.9% in both cases.14
(Table 1). In clinical practice, the large majority of There is some controversy over the benefit of early
patients with mitral valve IE present with positive surgery for native valve IE. The authors of one retro-
blood cultures and echocardiographic evidence of spective study of 546 patients with left-sided endo-
valvular involvement. Active endocarditis is defined carditis concluded that surgery for IE was not asso-
as ongoing infection in a patient who has not yet ciated with a survival benefit.18 Key limitations of
completed a full course of intravenous antibiotics. this report included a high operative mortality (27%)
The diagnosis of mitral valve IE is usually established and a noncontemporary series (1980-1998). The
by the time surgical evaluation is requested. Delayed large majority of contemporary series demonstrate
diagnosis of IE is common. the benefit of early surgery for left-sided endocardi-
tis.
BENEFIT OF OPERATION Current single-institution19-21 and national series6
IN ACTIVE ENDOCARDITIS of patients undergoing surgery for mitral valve IE
There have been no randomized controlled trials have reported mortality rates of less than 10% com-
in which investigators address the benefits, indica- pared to the overall 30% mortality rates reported for
tions, timing, and technique of operation for IE. All all patients diagnosed with left-sided IE. There are 2
Seminars in Thoracic and Cardiovascular Surgery ● Volume 23, Number 3 233
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