Review
Infective endocarditis: An intensive care perspective

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Summary

Infective endocarditis is a rising problem in the intensive care setting. Patients admitted to the intensive care unit (ICU) are at a high risk of developing infective endocarditis because of the frequent use of invasive monitoring and therapeutic devices in the intensive care environment. In particular, cardiac surgery patients are at a high risk of developing nosocomial infective endocarditis in the ICU. Staphylococci and Streptococci are the predominant organisms causing infective endocarditis in this setting, while fungal endocarditis remains a less frequent condition that may be on the rise. Infective endocarditis in the intensive care can be challenging to diagnose and manage. Morbidity and mortality from infective endocarditis can be high in the intensive care setting because of pre-existing pathologies in patients as well as the more complex nature of the disease in patients who need admission to the ICU. A multidisciplinary team approach is essential to improve clinical outcomes of patients with this condition. Particular emphasis has to be placed on the prevention of nosocomial endocarditis in the ICU through the use of strict aseptic conditions during placement and manipulation of invasive devices as well as appropriate endocarditis prophylaxis in selected patients.

Introduction

Infective endocarditis (IE) refers to an inflammation of the endocardium caused by infectious agents. IE was first described as a disease condition as early as in the 16th century.1 Since the first descriptions of IE, significant advances have been made in our understanding of the disease, its prevention, diagnosis and treatment. A number of people have contributed to these advances including Sir William Osler, who in 1885 drew a distinction between “simple” and “malignant” forms of endocarditis, which we now refer to as subacute and acute IE respectively.1, 2

The incidence of IE has essentially remained unchanged over the last two decades, ranging between 3 and 10 episodes/100,000 person-years.1, 3 However, the epidemiological profile of IE has changed dramatically in recent years with a large increase in the proportion of cases with Staphylococcal IE due to intravenous drug abuse, infection of prosthetic heart valves and the use of invasive vascular devices.3 Nosocomial IE (NIE), which is defined as infective endocarditis in patients admitted to a hospital at least 72 h prior to the onset of symptoms of IE or IE in patients with a history of an invasive procedure carried out in a recent hospital admission less than 8 weeks prior to onset of symptoms,4 has similarly increased in incidence and is a growing problem.

The diagnosis and management of infective endocarditis in the ICU setting can be quite challenging. ICU teams encounter patients with IE who are hemodynamically unstable due to severe sepsis, heart failure or cardiogenic shock as well as patients who have severe valvular pathology due to IE and require cardiac surgery.5 Patients are also admitted to the ICU after major cardiac surgery for post-operative care and are very susceptible to NIE and other nosocomial infections.6 Patients on ICU are in general more susceptible to developing IE due to the widespread use of invasive monitoring and therapeutic devices such as central venous lines, mechanical ventilation, in-dwelling urinary catheters, hemofiltration devices and so on.

Despite advances in diagnosis and treatment along with improved antimicrobial treatments and potentially curative surgery, infective endocarditis continues to cause significant morbidity and mortality.3, 7, 8, 9 Mortality from IE is particularly high in ICU patients ranging from 29 to 54%.10, 11, 12 This review article will provide a concise overview of the pathophysiology, diagnosis and management of IE and provides a specific update on recent developments in all aspects of IE in the ICU setting.

Section snippets

Causative organisms

There is limited data on the causative organisms for IE in ICU patients. A few data series available in literature on patients with IE in the ICU setting have found Staphylococci to be the most commonly isolated organisms9, 10, 11 with Streptococci being the second most common. In a study of 90 ICU patients with IE, Mouly et al. reported that majority (44%) of the cases were caused by Staphylococci, followed by Streptococci which were responsible for 25% cases.9 Methicillin Resistant

Pathophysiology

The endothelium represents the internal lining of heart valves and cavities. In normal conditions it forms a continuous smooth surface which, if subjected to injury, can become susceptible to fibrin and platelet deposits leading to the formation of sterile micro-vegetations.1, 12 This endothelial injury can occur as a result of high-velocity turbulent blood flow associated with certain valvular pathologies like aortic incompetence, mitral incompetence and ventricular septal defects17 or due to

Clinical features

IE may present with a variety of clinical manifestations including atypical symptoms, particularly in patients on ICU. Common presentations on the ICU are pyrexia of unknown origin; peripheral thromboembolism; neurological complications such as stroke or intracranial hemorrhage; hypotension; new or changing cardiac murmur; tachycardia; heart failure; unexplained rise in inflammatory markers; acute kidney injury and anemia8, 19, 20 (please see Table 1).

The classical manifestations of IE are not

Predictors of outcome

Various clinical factors have been associated with higher overall mortality in patients with IE and the majority of these factors are common predictors of outcome in ICU patients as well as in patients in general. These factors include older age,21 presence of heart failure, presence of severe sepsis, immunocompromised status, presence of acute kidney injury5, 8, 9, 12, 22, 23 and antimicrobial treatment failure.24 Other factors linked with increased mortality are prosthetic valve infection9, 25

Diagnosis

The diagnosis of IE is derived from a combination of clinical findings, laboratory investigations and imaging data. The Modified Duke’s Criteria can be used for the diagnosis of IE,28, 29 although these have not been specifically validated for the diagnosis of IE in the ICU setting (please see Table 3).

Essentially, diagnosis is based on strength of clinical suspicion in conjunction with evidence from blood cultures and imaging modalities such as echocardiography, CT and MRI. At least 3 sets of

Treatment

Treatment of IE includes antimicrobial therapy alone or in combination with surgery when indicated. The former should be instituted early, after at least three sets of blood culture samples have been taken from peripheral venous sites.23 Empirical antibiotics can be started based on local hospital policy and standard national or international guidelines such as those issued by the ACC or ESC. The microbiology team should be consulted in all cases to guide treatment as per local protocols. The

Prevention

As previously highlighted nosocomial IE is a growing problem particularly in the ICU. There is a clear need to have robust ICU protocols to prevent infections such as IE occurring as a result of invasive devices.42 Central venous catheter associated blood stream infections are common in the ICU setting and are known to cause IE in susceptible patients such as those with prosthetic valves, known valve disease or patients post-cardiac surgery.6, 20, 43, 44, 45 Adequate precautions and care should

Conclusions

IE is a condition which is increasingly encountered in the ICU. Mortality can be very high in this setting due to the higher complexity of cases admitted to ICU and the co-existing pathologies. The ICU stay itself represents a risk factor for nosocomial IE in susceptible patients groups. Diagnosis involves the identification of the causative organism by serial blood cultures (which allows for effective antibiotic therapy to be administered based on sensitivities) along with imaging studies.

Conflict of interest

The authors have no conflicts of interest to declare.

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