**3. Clinical symptoms, diagnosis, and imaging**

Infective endocarditis is a condition whose presentation may vary greatly, which consequently may make the diagnosis elusive, conferring a significant delay in initiation of treatment. The presenting symptoms stem from several distinct pathophysiological mechanisms, and any combination of these may occur in any given individual:


Pathologic criteria


Showing active endocarditis

Clinical criteria


Possible infective endocarditis


Rejected


Definite infective endocarditis


These mechanisms are reflected in the diagnostic criteria (the Duke criteria) provided in **Table 1** [6]. To accurately make an IE diagnosis, it is crucial to (a) perform a thorough clinical examination, (b) acquire adequate microbiological samples, and (c) ensure that correct radiological imaging is carried out. As to the latter, the cornerstone of radiological imaging has long been echocardiography: preferably with a transesophageal approach. Other modalities, such as ECG-triggered computerized tomography and positron emission tomography, are sometimes used in clinical practice, but are as yet not included in the Duke criteria [5].

### **4. Microbiology, antibiotic treatment, and surgery**

The most common etiologic agents in IE are Gram-positive bacteria, which are responsible for more than 90% of cases. IE caused by Gram-negative bacteria and fungi does occur but rarely. While traditionally the major bacterial finding has been streptococcal species, later decades have seen a continuing rise of *S. aureus* [3].

 Regardless of etiology, treatment consists of a long course of high-dose antibiotics, which are generally administered intravenously for the entire duration. Length of the treatment is usually 2–4 weeks but may be longer in complicated cases—particularly in those involving foreign material in the bloodstream. Due to the high total drug exposure, it is imperative to use pharmaceuticals which are well tolerated by the majority of patients. As in other severe infections, antibiotics of the betalactamase class are preferred when applicable. These drugs are distinguished by a combination of high efficacy and good tolerability [7].

Pharmaceutical treatment alone is often insufficient, however. Thoracic surgery is required in 25–50% of cases during acute infection and 20–40% during convalescence. Surgery is effective (a) as a means of source control (b) in preventing embolization and (c) as a means to repair structural cardiac damage [8]. Procedural risk is significant, however, and the decision to operate should be taken on an individual basis and in collaboration with representatives of appropriate clinical and diagnostic specialties. To this end it is recommended that decisions are taken by a unit known as the endocarditis team [9].
