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Are All Echocardiographic Findings Equally
Predictive of Prosthetic Endocarditis?

Ricardo E Ronderos, MD, PhD

Hospital San Juan de Dios, Instituto de Cardiología La Plata,
Universidad Nacional de La Plata, Argentina

   Echocardiography has shown a big impact in diagnosis of infective endocarditis. Since Durack's criteria, ultrasound images became mayor criteria for such diagnosis, representing the only way to show anatomic evidence of endocardial involvement during a sepsis. Until Durack's experience as published, only anatomopathologic findings from surgery, autopsy or emboli material were the unique evidence of septic endocardial involvement (Von Reyn).

   Durack's criteria were changing on time in concordance of more information obtained using developed ultrasound techniques. Special scenarios, as cardiac prosthesis, appear as complex fields for echo diagnosis.

   Prosthetic materials, surgical maneuvers, surgical techniques and the impossibility of infection to compromise mechanical devices, made the classic "vegetation criteria" suboptimal for endocarditis diagnosis in-patients with valve prosthesis.

    Postoperative fever, is frequent, in coincidence with anatomic changes due to surgical procedures as separate sutures around prosthetic ring, cloth and haematomas around aorta or fibrous valve rings and echo free spaces secondary to changes in normal anatomy induced by surgical reconstruction.

   Use of transesophageal echocardiography with broad band high frequency transducers, increases dramatically the ultrasound images resolution. This fact allows echocardiographers to look carefully to a lot of anatomical findings frequently very difficult to explain in terms of "normal postsurgical findings" or mayor criteria for endocarditis diagnosis in patients with valve replacement and fever with hemolyisis and or new murmurs.

   Blood cultures are the other main criteria for such diagnosis, but negative blood cultures are unfortunately frequent in the cohort of patients with suspicion of early endocarditis (antibiothical prophylaxis after surgery, presence of multiple venous invasions during postop, and antibiotics administration after hospital period for concurrent infections are common causes of such high percentage of negative cultures). On the other hand, late prosthetic endocarditis is usually due to slow growing type of microorganisms (coagulase negative staphylococcus, HACECK group, etc.) that also have low rate of positive blood cultures. In this particular scenario echocardiography became the great value tool for endocarditis diagnosis.

   Unstable prosthesis, aortic or mitral rings' rupture with fistulae are easily recognized as endocarditis complications. But smaller signs as "vegetation" in biologic prosthetic devices, or abscess without other typical findings or 1 or 2+ periprosthetic leaks and regurgitation, could be present without any significant infection.

   Vegetation was well defined by Durack's criteria as tiny, high mobile with high velocity fluttering structures related to cardiac valves. It is not infrequent to see this kind of structures in abnormally degenerated non-infected bioprosthesis; this is a common cause of false positive echo diagnosis in suspicion of endocarditis.

   Echo free spaces around valve rings, in particular around aortic valve ring are secondary in most cases to abscess or pseudoaneurysms due to prosthetic infection (Figure 1 and 2), in those cases inflammatory material as debris or vegetation are usually present in combination with such echo free spaces. But seldom those echolucent areas are secondary to infection when they appear alone without other mayor signs of endocardial infection as vegetation or high degree of periprosthetic leaks.

Figure 1

Figure 2

   It is possible to have 3-4+ periprosthetic regurgitation (Figure 3) without prosthetic infections, but in a clinical high suspicion clinical scenario of endocarditis, those kind of anatomic findings are frequently highly predictive of prosthetic endocarditis, and in those cases are usually related with other typical endocarditis signs as vegetation, abscess or pseudoaneurysms.

Figure 3

   On the other side very small periprosthetic leaks (Figure 4), are usually seen after surgery if a high resolution TEE is performed for any causes. Separate type of surgical sutures allow during unexpected period of time the presence of those 1-2+ periprosthetic leaks without any relation with endocardial involvement. In our experience those types of anatomic findings are not predictive at all for diagnosis of endocarditis unless they are related with other highly predictive signs as vegetation, abscess and or pseudoaneurisms. In those patients endocarditis diagnosis should be rule out, and TEE should be performed as many times as it was necessary if high clinical suspicion of endovascular infection is present. If any other areas could explain a sepsis situation, blood cultures are negative and repeated TEE not show progression to high degree regurgitation or new findings appears, those type of small regurgitation periprosthetic leaks should be not consider as endocarditis mayor criteria diagnosis.

Figure 4

   During a follow up of 24 patients with suspicion of endocarditis with only that small regurgitation during a media of 38 months, nobody developed a real prosthetic endocarditis.

   These concepts need to be repeated by larger series of patients and in different groups, but at the present time, seems to be a good practice not to consider small leaks as signs of prosthetic endocarditis. Also vegetation alone in bioprosthesis should be consider carefully to avoid false positive diagnosis. Echo free spaces, as anatomic findings alone (with negative blood cultures for instance) should be also evaluated carefully to increase echocardiography specificity in the field of prosthetic endocarditis.


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