Diagnosis of culture-negative endocarditis: the role of the Duke criteria and the impact of transesophageal echocardiography

Small vessel vasculitis associated with culture-negative infective endocarditis related to a cardiac device: a case report

Background

Culture-negative endocarditis is uncommon, occurring in less than a third of all cases of infective endocarditis (IE). Culture-negative IE related to a cardiac device is an even greater diagnostic challenge due to its insidious presentation, with onset of symptoms ranging between 3 and 12 months after device implantation. Sensitivity of the modified Duke’s criteria remains low in culture-negative and cardiac device-related IE (CDRIE) since classical signs and symptoms of IE are often absent. Small vessel vasculitis has been reported as an immune response to IE. Recognizing immunological phenomenon related to IE is of paramount clinical importance, prompting the search for an underlying infection and avoiding the use of immunosuppressive medications which would otherwise result in an adverse outcome.

Case summary

An 81-year-old Caucasian male presented to the ambulatory medical unit with a two-week history of a symmetrical, generalized purpuric rash. He had an indwelling permanent pacemaker following a transcatheter aortic valve implantation for severe aortic stenosis five years ago. Blood tests showed an iron deficiency anaemia, thrombocytopenia and normal renal function, both CRP and ESR were raised at 61  and 30 mm/hr, respectively. Skin biopsy demonstrated small vessel cutaneous vasculitis. Transthoracic echocardiography revealed a mobile mass measuring 0.9 × 1.7 cm, confirmed on transoesophageal echocardiogram as pacing lead endocarditis. Blood cultures were persistently negative. The patient underwent pacemaker lead extraction, following which the vasculitic rash improved.

Discussion

Blood cultures in IE are more likely to be negative if there is a prior antibiotic administration or causative micro-organisms with limited proliferation which fail to grow in conventional media conditions. Transesophageal echocardiography (TOE) offers improved sensitivity and diagnostic yield when compared to transthoracic echocardiography (TTE) in patients with a high clinical suspicion of CDRIE. The evidence in the literature describing culture-negative IE associated with small vessel vasculitis is limited. However, it is recognized that cutaneous small vessel vasculitis may be associated with an underlying bacterial infection. IE produces an inflammatory response, resulting in the deposition of circulating immune complexes and cutaneous signs which are included in the modified Duke’s criteria to aid diagnosis. Management of CDRIE requires a multi-disciplinary team approach with an ‘Endocarditis Team.’ Pacemaker lead infection requires transvenous lead extraction if it is a newly implanted lead. Locking stylets, extraction sheaths or snare retrieval are usually required in cases of older implanted leads. Surgical lead extraction remains the gold standard for larger vegetations (>20 mm) or associated valve endocarditis.

Cutibacterium acnes: An emerging pathogen in culture negative bacterial prosthetic valve infective endocarditis (IE)

Cutibacterium acnes (previously known as Propionibacterium) infections are reportedly increasing in patients with implanted foreign material. Though it is a rare cause of bacterial endocarditis, patients with implanted prosthetic valves and devices have potential increased risk. Cutibacterium species are an ubiquitous environmental surface contaminant and typically difficult to culture, in case of high suspicion for infective endocarditis extended duration incubation of blood or any tissue sample and 16S RNA sequencing of any tissue sample is helpful for a microbiological identification. We report a case of a 50 year old male with culture negative prosthetic valve endocarditis in which the pathogen was identified by molecular testing 16S RNA gene sequencing.

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Prosthetic valve endocarditis.

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Cutibacterium acnes.

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16S gene sequencing.

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Management challange for prostetic valve endocarditis.

2020 ACC/AHA Guideline for the Management of Patients With Valvular Heart Disease: Executive Summary: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines

AIM

This executive summary of the valvular heart disease guideline provides recommendations for clinicians to diagnose and manage valvular heart disease as well as supporting documentation to encourage their use.

METHODS

A comprehensive literature search was conducted from January 1, 2010, to March 1, 2020, encompassing studies, reviews, and other evidence conducted on human subjects that were published in English from PubMed, EMBASE, Cochrane, Agency for Healthcare Research and Quality Reports, and other selected database relevant to this guideline. Structure: Many recommendations from the earlier valvular heart disease guidelines have been updated with new evidence and provides newer options for diagnosis and treatment of valvular heart disease. This summary includes only the recommendations from the full guideline which focus on diagnostic work-up, the timing and choice of surgical and catheter interventions, and recommendations for medical therapy. The reader is referred to the full guideline for graphical flow charts, text, and tables with additional details about the rationale for and implementation of each recommendation, and the evidence tables detailing the data considered in developing these guidelines.

Ruptured mitral valve abscess with mitral incompetence in culture negative infective endocarditis: case report

Introduction

Perivalvular abscess in native valve infective endocarditis (IE) is associated with significantly increased mortality.

Case description

Herein, we report a 29 year old Indian male who presented with culture negative IE with perivalvular abscess and severe mitral regurgitation requiring mitral valve replacement.

Discussion

Initial approach is very difficult in terms of when IE presents as culture negative. This case highlights the important role of echocardiography in the management of culture negative IE.

Fungal mobile mass on echocardiogram: native mitral valve Aspergillus fumigatus endocarditis

The most common type of infective endocarditis is bacterial endocarditis. However, fungal infections have been seen more frequently, mostly in the immunocompromised population. We report a case of invasive Aspergillus fumigatus native mitral valve endocarditis. The patient received appropriate empiric antifungal treatment with a combination of liposomal amphotericin B and flucytosine, associated with surgical debridement, valve replacement and chordae tendineae repair. Despite receiving the standard treatment of Aspergillus endocarditis, and susceptibility of the microorganism to the antifungal regimen, the patient, unexpectedly, developed early-onset septic emboli. It is surprising to see that the patient had developed such complications early, despite attempts to eliminate the source of infection with surgical intervention.

A rare case of behçet disease presenting with pyrexia of unknown origin, pulmonary embolism, and right ventricular thrombus

Behçet disease is a systemic vasculitis characterized by recurrent oral and genital ulcers and uveitis. We describe a rare case of a 43-year-old woman with Behçet disease who was admitted for pyrexia of unknown origin, cough, dyspnea, and chest pain. Her computerized tomography scan revealed pulmonary embolism and right ventricular thrombus. She was treated with anticoagulation for pulmonary embolism and right ventricular thrombus. She was well during her last follow-up.

Is it toxoplasma encephalitis, HIV encephalopathy or brain tuberculoma?

A 31-year-old Malaysian man was presented with an episode of seizures by the roadside, after having been recently diagnosed as HIV positive accompanied with miliary tuberculosis. On physical examination, he was oriented to person, but not to time or place. There was no neck stiffness or papilloedema. The other systemic examination was unremarkable. Chest examination revealed crepitations at the upper zone of the right lung. After diagnosis suspicion, the case was confirmed as toxoplasma encephalitis by MRI and serological tests. Patient was treated with trimethoprim/sulfamethoxazole 480-2400 mg/day with folinic acid supplement for 60 days. Two months later, a repeat brain MRI showed resolution of the cerebral lesions.

Are histopathological findings of diagnostic value in native valve endocarditis?

BACKGROUND

Optimal management of infective endocarditis (IE) depends on the early detection of IE-causing pathogens and on appropriate antimicrobial and surgical therapy. The current guidelines of the European Society of Cardiology (ESC) recommend histopathological examination as the gold standard for diagnosing IE Habib et al. (Eur Heart J 30:2369-2413, 2005). We hypothesize that histopathological findings do not provide additional information relevant to clinical decision-making.

METHODS

We retrospectively reviewed a cohort of patients who had undergone surgery for native valve endocarditis (NVE) at the University Hospital Regensburg between September 1994 and February 2005. All episodes of intraoperatively confirmed endocarditis during this period were included in the study. Data were retrieved from surgical records, microbiological and histopathological reports, and medical files of the treating as well as admitting hospital. Pathogens were correlated with the site of manifestation of the affected heart valve and with clinical and histopathological findings.

RESULTS

A total of 163 episodes of NVE were recorded and entered into our study for analysis. The valves affected were the aortic valve (45 %), the mitral valve (28 %), the aortic and mitral valve (22 %), and other valves (5 %). IE-causing pathogens were Staphylococcus aureus (22 %), viridans streptococci (18 %), enterococci (10 %), streptococci other than Streptococcus viridans (9 %), coagulase-negative staphylococci (5 %), miscellaneous pathogens (4 %), and culture-negative endocarditis (33 %). Infection with S. aureus was associated with high rates of sepsis, septic foci, and embolic events, while patients with enterococcal IE showed the highest rate of abscesses. Mortality rate in all subgroups was low without significant differences. However, histopathological findings correlated poorly with the pathogen involved and showed only few significant associations that were without clinical relevance.

CONCLUSIONS

The clinical presentation of IE depends on the pathogen involved. Among the episodes of NVE examined, the histopathological examination of resected heart valves did not show any pathogen-specific morphological patterns and therefore did not provide any additional information of clinical value. Based on our findings, we recommend complementary cultures of the resected materials (valve tissue, thrombotic material, pacer wire) and implementation of molecular diagnostic methods (e.g., broad-range PCR amplification techniques) instead of histopathological analyses of resected valve tissue.

Reassessment of blood culture-negative endocarditis: its profile is similar to that of blood culture-positive endocarditis

INTRODUCTION AND OBJECTIVES

Left-sided infective endocarditis with blood culture-negative has been associated with delayed diagnosis, a greater number of in-hospital complications and need for surgery, and consequently worse prognosis. The aim of our study was to review the current situation of culture-negative infective endocarditis.

METHODS

We analyzed 749 consecutive cases of left-sided infective endocarditis, in 3 tertiary hospitals from June 1996 to 2011 and divided them into 2 groups: group I (n=106), blood culture-negative episodes, and group II (n=643) blood culture-positive episodes. We used Duke criteria for diagnosis until 2002, and its modified version by Li et al. thereafter.

RESULTS

Age, sex, and comorbidity were similar in both groups. No differences were found in the proportion of patients who received antibiotic treatment before blood culture extraction between the 2 groups. The interval from symptom onset to diagnosis was similar in the 2 groups. The clinical course of both groups during hospitalization was similar. There were no differences in the development of heart failure, renal failure, or septic shock. The need for surgery (57.5% vs 55.5%; P=.697) and mortality (25.5% vs 30.6%; P=.282) were similar in the 2 groups.

CONCLUSIONS

Currently, previous antibiotic therapy is no longer more prevalent in patients with blood culture-negative endocarditis. This entity does not imply a delayed diagnosis and worse prognosis compared with blood culture-positive endocarditis. In-hospital clinical course, the need for surgery and mortality are similar to those in patients with blood culture-positive endocarditis. Full English text available from:www.revespcardiol.org.

The role of 18F-FDG PET or PET/CT in the detection of fever of unknown origin

Even with the recent advance in diagnostic tools and techniques, fever of unknown origin (FUO) remains a clinical challenge. A wide range of diseases, mainly infections, autoimmune conditions (inflammatory diseases), malignancies and miscellaneous can cause FUO. Positron emission tomography (PET) or positron emission tomography/computed tomography (PET/CT) scanning makes a great contribution to the diagnosis and differential diagnosis of FUO due to the high sensitivity of pathological accumulation of 18F-FDG. The diagnostic yield of PET/CT is higher than traditional radiographic imaging and other nuclear medicine scanning. Owing to the numerous advantages of PET/CT including high sensitivity and the ability to perform whole-body scans, many rare diseases presenting with FUO can be detected and the spectrum of diseases that can exhibit FUO has been increasing. Recent studies utilizing FUO are discussed in this paper. However, there are limited data available about the role of 18F-FDG PET or PET/CT in evaluation of FUO.

[Infectious endocarditis in intensive care patients]

Infectious endocarditis is a rare disease with high mortality. Epidemiological changes in recent years, the emergence of new risk factors, and the increasing use of intravasal prosthetic materials has led to changes in not only the clinical appearance of this disease but also in its diagnosis and treatment. Early diagnosis of infectious endocarditis is crucial. However, the often unspecific symptoms and the changes in its epidemiologic profile pose a challenge for the treating physician. This is especially true since the incidence of hospital-acquired, "nosocomial" cases of infectious endocarditis is increasing and often affects severely ill patients in intensive care units (ICU). There are diagnostic and therapeutic algorithms to guide the physician from an early diagnosis to an adequate treatment of the disease. In some critically ill patients, only surgery in combination with antimicrobial treatment may lead to complete eradication of the infectious disease. This review aims to subsume the guidelines, paying special attention to aspects that are important for intensive care and emergency doctors.

Use of echocardiography in the diagnosis and management of infective endocarditis

The first use of echocardiography in infective endocarditis (IE) was described in 1973. Since then, echocardiography has emerged as a major tool for the diagnosis and management of this disease. In general, transthoracic echocardiography (TTE) is adequate for diagnosing IE in cases where cardiac structures-of-interest are well visualized. Specific situations where transesophageal echocardiography is preferred over TTE include the presence of a prosthetic device, suspected periannular complications, children with complex congenital cardiac lesions, selected patients with Staphylococcus aureus bacteremia, and certain pre-existing valvular abnormalities that make TTE interpretation problematic (eg, calcific aortic stenosis). Echocardiography is also useful for risk stratification. Evidence suggests that vegetation size can predict embolic complications, although the data are inconsistent. Careful clinical assessment is essential to the proper use of echocardiography in diagnosing IE, visualizing complications related to IE, and evaluating candidacy for surgical intervention.

Culture negative endocarditis caused by Bartonella henselae in a child with congenital heart disease

A 9-year-old white male with congenital aortic and subaortic stenosis palliated by the Ross-Konno procedure presented with culture-negative endocarditis. Serologic studies and polymerase chain reaction testing of resected homograft valvular tissue provided evidence of Bartonella henselae as the etiology. B. henselae can cause endocarditis in children, particularly those with underlying valvular disease. Serologic testing for B. henselae should be considered in children with culture-negative endocarditis.

The potential impact of contemporary transthoracic echocardiography on the management of patients with native valve endocarditis: a comparison with transesophageal echocardiography

BACKGROUND

Between 1987 and 1994, several studies demostrated transthoracic echocardiography (TTE) to be less sensitive than transesophageal echocardiography (TEE) in detecting native valve endocarditis. Recent technologic advances, especially the introduction of harmonic imaging and digital processing and storage, have improved TTE image quality. The aim of this study was to determine the diagnostic accuracy of contemporary TTE.

METHODS

Between 2003 and 2007, 75 patients underwent both TTE and TEE for clinically suspected infective endocarditis. The diagnostic accuracy of TTE was assessed using transesophageal echocardiography as the gold standard for diagnosis of endocarditis.

RESULTS

Of the 75 patients in this study, 33 were found to be positive by TEE. The sensitivity for detection of infective endocarditis by TTE was 81.8%. It provided good image quality in 81.5% of cases; in these patients sensitivity was even greater (89.3%).

CONCLUSION

Contemporary TTE has improved the diagnostic accuracy of infective endocarditis by ameliorating image quality; it provides an accurate assessment of endocarditis and may reduce the need for TEE.

German guidelines for the diagnosis and management of infective endocarditis

This Gudelines are the translation of the German Guidelines for the Diagnosis and Management of Infective Endocarditis, which were prepared by the Working Group on Infective Endocarditis of the Paul-Ehrlich-Society and the German Society for Cardiology, Heart, and Circulatory Research in cooperation with the Deutsche Gesellschaft für Thorax-, Herz und Gefässchirurgie (DGTHG; German Society for Thorax-, Cardiac-, and Vascular Surgery), the Deutsche Gesellschaft für Infektiologie (DGI; German Society for Infectious Diseases), the Deutsche Gesellschaft für Internistische Intensivmedizin und Notfallmedizin (DGIIN; German Society for Internal Intensive Care Medicin and Emergency Medicine), the Deutsche Gesellschaft für Hygiene und Mikrobiologie (DGHM; German Society for Hygiene and Microbiology) and the Deutsche Gesellschaft für Innere Medizin (DGIM; German Society for Internal Medicine) (Naber CK et al. [S2 Guideline for diagnosis and therapy of infectious endocarditis] Z Kardiol. 2004;93:1005-21). The Guidelines provide recommendations for the diagnosis and management of infective endocarditis.

Endocarditis at a tertiary hospital: reduced acute mortality but poor long term prognosis

The outcome in 132 patients with infective endocarditis diagnosed in accordance with the Duke criteria at a tertiary hospital in Denmark in the period 1998-2000 is reported. The total in-hospital mortality was 15%. Indications are that in-hospital mortality over the last decade has been reduced by around a quarter. Mortality after 3 months was 17% (CI 29%), after 3 years 32% (CI 16-47%) and after 5 years 39% (CI 22-55%). This 5-years mortality was 5 times that of an age and gender matched background population. After follow-up for 5-8 y, mortality was highest for prosthetic valve endocarditis (63% vs. 39%, p = 0.05). Heart surgery was performed in 51% of the cases. Patients who underwent surgery had a lower mortality at follow-up (36% vs. 52%, p = 0.04). The 5-year mortality was 30% (CI 9-52%) for patients treated with surgery and 48% (CI 23-72%) for patients treated without surgery. In multivariable analysis surgery was not an independent predictor for lower long-term mortality. Surgery was however an independent predictor for lower intermediate-term mortality. It is concluded that surgery may be associated with lower short- and intermediate-term mortality, while the effect might decline in the long-term. High age, prosthetic valve endocarditis, and Staphylococcus aureus endocarditis were independent predictors for high mortality. Although improvements have occurred over recent years, infective endocarditis is still a high mortality disease.

Role of Echocardiography in Diagnosis and Management of Endocarditis

Echocardiography plays an increasingly important role in diagnosis and management of patients with infective and noninfective endocarditis. Significant changes to diagnostic criteria for endocarditis have occurred, and there are evolving trends associated with an older population presenting with endocarditis, greater numbers of patients with prosthetic heart valves and complex congenital heart disease, and an exponential increase in the numbers of patients eligible for pacing and defibrillator implants. The diagnostic accuracy of echocardiography has been enhanced by developments such as multiplanar transesophageal probes, real-time three-dimensional echocardiography, and intracardiac echocardiography. Standard echocardiography techniques now define the need for and timing of surgical intervention in endocarditis and may help determine the duration of treatment and follow-up after diagnosis.

Infective endocarditis: a five-year experience at a tertiary care hospital in Pakistan

OBJECTIVES

Infective endocarditis is common and data regarding its pattern and outcome from developing countries is sparse. We therefore examined the spectrum, demographics and clinical features of infective endocarditis and sought to determine the factors affecting its clinical outcome.

PATIENTS AND METHODS

Over a five-year period at our university hospital in Karachi, Pakistan, we identified 66 patients with infective endocarditis and compared their clinicoepidemiologic features and outcomes to subjects in the West.

RESULTS

The male:female ratio was 2:1; overall median age was 24 years (35.5 years for men and 13.5 years for women) (p < 0.001). Median duration of symptoms before presentation was 20.5 days. Major predisposing cardiac abnormalities included congenital (50%) and rheumatic (23%) lesions, and a history of heart surgery (17%). Causative organisms and valvular sites of infection were similar to those seen in developed countries. Blood culture-negative infective endocarditis was found in 48% of cases. Renal failure was more frequent among culture-positive patients (p = 0.055). Risk factors for mortality included neurologic (p = 0.003) and embolic (p = 0.02) complications, renal (p = 0.03) and left ventricular failure (p = 0.002), and a history of cardiac surgery (p = 0.026). Overall mortality was 27%.

CONCLUSIONS

Patients with infective endocarditis in Pakistan exhibit significant differences compared to their counterparts in the West, including younger age at presentation, incidence of predisposing cardiac conditions, and gender differences reflecting sociocultural bias. Neurologic and embolic complications, renal failure and heart failure predict a worse outcome.

Are all echocardiographic findings equally predictive for diagnosis in prosthetic endocarditis?

OBJECTIVE

The purpose of this study was to analyze the predictive value of different anatomic echocardiographic findings for diagnosis of prosthetic endocarditis.

BACKGROUND

Prognosis in endocarditis has improved in recent years after the wide acceptance of new clinical diagnostic criteria. One of the most important issues in clinical diagnosis is to use echocardiography for identification of endocardial involvement, but prosthetic material impairs echo quality.

METHODS

In all, 49 patients with 58 episodes of suggested prosthetic endocarditis were prospectively studied using transthoracic and transesophageal echocardiography. The patients were divided into two groups: group A, patients with 34 episodes of definite endocarditis according to Durack's criteria; and group B, patients with 24 episodes who were eventually classified as not having endocarditis, either by surgical exploration or by a mean of 32.6 months (range: 8-38 months) of follow-up.

RESULTS

In group A, valve dehiscence was observed in 4 episodes of suggested endocarditis, pseudoaneurysms in 3, fistulae in 2, and moderate to severe perivalvular regurgitation in 15. No patient in group B had these abnormalities (P <.001). Vegetations were present in 17 episodes in group A (50%) versus 1 in group B (9%; P <.001); perivalvular abscesses were seen in 19 episodes in group A (56%) versus 1 in group B (P <.001). Mild perivalvular regurgitation was observed in only 1 episode for group A (3%) and in 14 episodes for group B (58%; P <.01). The presence of any of the above echocardiographic finding, when used in combination with the exclusion of mild perivalvular regurgitation, had a positive and negative predictive value for diagnosing endocarditis of 94% and 96%, respectively. Isolated mild perivalvular regurgitation had a poor positive predictive value (6%).

CONCLUSION

Isolated mild perivalvular regurgitation should not be used as diagnostic criteria in patients with suggested prosthetic valve endocarditis.

Using 18-fluoro-2-deoxyglucose positron emission tomography in detecting infectious endocarditis/endoarteritis

RATIONALE AND OBJECTIVES

We evaluated the effectiveness of positron emission tomography (PET) with 18-fluoro-2-deoxyglucose (FDG) in the detection of infectious endocarditis/endoarteritis.

MATERIALS AND METHODS

For this study, we recruited 6 patients (4 women, 2 men; age range, 35 - 78 years; mean age, 55.8 +/- 16.8 years) who were clinically diagnosed as having infective endocarditis/endoarteritis by their echocardiographic findings and by Duke criteria.

RESULTS

For all 6 patients, we also found increased FDG uptakes in the corresponding areas detected in echocardiography.

CONCLUSION

FDG-PET appears to be a promising tool in diagnosing infective endocarditis/endoarteritis, and further prospective studies on a large scale to fully exploit the usefulness of FDG-PET for infective endocarditis/endoarteritis are needed.

Gram stain, culture, and histopathological examination findings for heart valves removed because of infective endocarditis

Retrospective chart review was undertaken for 480 patients who underwent a total of 506 valve replacements or repair procedures for infective endocarditis. The influence of preoperative antimicrobial treatment on culture, Gram stain, and histopathological examination findings for resected valve specimens was examined. When valves were removed before the end of treatment, organisms were seen on the Gram stain of ground valve material performed in the microbiology laboratory and on Gram-stained histopathological sections in 231 (81%) of 285 and 140 (67%) of 208 specimens, respectively (P=.0007). Gram-positive cocci were either cultured from or observed in excised valve tissue in 42 (67%) of 63 episodes involving negative preoperative blood cultures. Positive Gram stain results for microbiological specimens should be reintroduced into the definite pathological criteria for infective endocarditis. When deciding on how long to continue antimicrobial therapy after valve replacement for endocarditis, valve culture results should be the only laboratory finding taken into account, because it takes months for dead bacteria to be removed from sterile vegetations.

Blood culture negative endocarditis: analysis of 63 cases presenting over 25 years

OBJECTIVE

To analyse cases of blood culture negative endocarditis (BCNE) seen at St Thomas' Hospital, London, between 1975 and 2000.

METHODS

Data on all episodes of endocarditis with negative blood cultures seen at St Thomas' Hospital between 1975 and 2000 were collected prospectively and analysed retrospectively.

RESULTS

Sixty three patients with BCNE were seen during the study period: 48 (76%) with native and 15 (24%) prosthetic valve infection. BCNE accounted for 12.2% of the 516 cases of endocarditis seen at St Thomas' Hospital. The diagnosis of endocarditis was clinically definite by the Duke criteria in only 21% (7 of 34) of cases of pathologically proven native valve endocarditis but in 62% (21 of 34) of cases by the St Thomas' modifications of the criteria. Comparable figures for the 11 cases of pathologically proven prosthetic valve endocarditis were 45% and 73%. Despite negative blood cultures a causative organism was identified in 31 (49%) of the 63 cases: in 15 by serology (8 Coxiella burnetii, 6 Bartonella species, and 1 Chlamydia psittaci); in 9 cases by culture of the excised valve; in 3 by microscopy of the excised valve, on which large numbers of Gram positive cocci were seen although the culture was sterile; and in the other 4 by isolation from a site other than the excised valve (2 respiratory specimens, 1 from the pacemaker tip, and 1 from an excised embolus). In addition 5 of the 6 cases of Bartonella infection were confirmed by polymerase chain reaction study of the excised valve. Two thirds of the 32 patients for whom no pathogen was identified had received antibiotics before blood was cultured. Thus truly "negative" endocarditis was very uncommon (6% of the cases).

CONCLUSION

If blood cultures are negative in definite or suspected endocarditis, serum should be analysed for Bartonella, Coxiella, and Chlamydia species antibodies, and the excised valve or (rarely) embolus should be analysed by microscopy, culture, histology, and relevant polymerase chain reaction. Other specimens may be relevant. The Duke criteria performed poorly in BCNE; St Thomas' additional minor criteria gave more definite diagnoses.

Role of echocardiography in the diagnosis and management of infective endocarditis

Infective endocarditis is a life-threatening disease with significant morbidity and mortality. Accurate and early diagnosis for initiation of effective treatment is essential in improving patient outcome. Echocardiography is currently the primary modality for the detection of vegetations and cardiac complications that result from endocarditis. Technological advances in echocardiography, particularly the development of transesophageal echocardiography (TEE), have revolutionized the diagnosis and management of infective endocarditis. With the enhanced resolution provided by TEE, vegetations and paravalvular complications can be reliably detected. Transthoracic and transesophageal echocardiography provides complementary information for patient management and follow-up, and is best used in conjunction with clinical data. By means of its high sensitivity and negative predictive value, TEE is essential in the evaluation of prosthetic valve endocarditis and the paravalvular complications of IE. All patients with suspected infective endocarditis should undergo transthoracic echocardiography, and most of these patients should also undergo TEE evaluation. The role of new technology such as harmonic and three-dimensional imaging is yet to be determined.

Effect of electrical stimulus parameters on the development and propagation of action potentials in short excitable fibres

Intracellular action potentials (IAPs) produced by short fibres in response to their electrical stimulation were analysed. IAPs were calculated on the basis of the Hodgkin-Huxley (1952) model by the method described by Joyner et al. (1978). Principal differences were found in processes of activation of short (semilength L less than 5 lambda) and long fibres under near-threshold stimulation. The shorter the fibre, the lower was the threshold value (Ithr). Dependence of the latency on the stimulus strength (Ist) was substantially non-linear and was affected by the fibre length. Both fibre length and stimulus strength influenced the IAP amplitude, the instantaneous propagation velocity (IPV) and the site of the first origin of the IAP (and, consequently, excitability of the short fibre membrane). With L less than or equal to 2 lambda and Ithr less than or equal to Ist less than or equal to 1.1Ithr, IPV could reach either very high values (so that all the fibre membrane fired practically simultaneously) or even negative values. The latter corresponded to the first origin of the propagated IAP, not at the site of stimulation but at the fibre termination or at a midpoint. The characters of all the above dependencies were unchanged irrespective of the manner of approaching threshold (variation of stimulus duration or its strength). Reasons for differences in processes of activation of short and long fibres are discussed in terms of electrical load and latency. Applications of the results to explain an increased jitter, velocity recovery function and velocity-diameter relationship are also discussed.