Cardiac infections: focus on molecular diagnosis

Blood culture negative endocarditis in the modern era of 16S rRNA sequencing

Blood culture negative endocarditis (BCNE) accounts for up to 20% of infective endocarditis. While the most common cause of BCNE remains the initiation of antibiotics prior to culture, intracellular organisms such as Coxiella and Bartonella spp account for a significant proportion of cases. Identifying the infecting organism remains important to ensure optimal antimicrobial treatment. However, these organisms can be difficult to diagnose. We outline a systematic approach to BCNE. Over half of patients with infective endocarditis now undergo early surgery and 16S ribosomal ribonucleic acid (rRNA) polymerase chain reaction (PCR) of excised tissue can be vitally important to secure a diagnosis. Molecular testing is likely to become a key tool in improving outcomes from BCNE and contribute to an improved understanding of the aetiology. We advocate modifying the Duke criteria to incorporate organisms identified on molecular testing, including 16S rRNA PCR, in particular from explanted tissue.

Myocarditis

Myocarditis is an inflammatory disease of the heart that can cause devastating disease in otherwise healthy children. Inciting agents such as viral infection cause direct damage to the myocardial cells, which triggers an inflammatory response that enhances myocardial toxicity and associated morbidity. Severe cases typically present with respiratory distress and cardiovascular collapse, whereas subclinical cases are unnoticed by the medical community. The initial workup in suspected cases should include an electrocardiogram, chest radiograph, and cardiac troponin T. Treatment is concentrated on hemodynamic stabilization with optimization of heart failure management, dysrhythmia protocol, and supportive therapy. The purpose of this review was to provide the emergency medicine practitioner a concise and current review of the basic pathophysiology as well as a functional and evidence-based approach to the diagnosis and treatment of myocarditis in the pediatric population.

Classification and histological, immunohistochemical, and molecular diagnosis of inflammatory myocardial disease

In the WHO 1996 classification of cardiomyopathies, myocarditis is defined as an "inflammatory disease of the myocardium associated with cardiac dysfunction" and is listed among "specific cardiomyopathies". Myocarditis is diagnosed on endomyocardial biopsy (EMB) by established histological, immunological, and immunohistochemical criteria, and molecular techniques are recommended to identify viral etiology. Infectious, autoimmune, and idiopathic forms of inflammatory cardiomyopathy are recognized that may lead to dilated cardiomyopathy. According to Dallas criteria, myocarditis is diagnosed in the setting of an "inflammatory infiltrate of the myocardium with necrosis and/or degeneration of adjacent myocytes, not typical of ischemic damage associated with coronary artery disease". The majority of experts in the field agree that an actual increase in sensitivity of EMB has now been reached by using immunohistochemistry together with histology. A value of >14 leukocytes/mm(2) with the presence of T lymphocytes >7 cells/mm(2) has been considered a realistic cut off to reach a diagnosis of myocarditis. The development of molecular biological techniques, particularly amplification methods like polymerase chain reaction (PCR) or nested-PCR, allows the detection of low copy viral genomes even from an extremely small amount of tissue such as in EMB specimens. Positive PCR results obtained on EMB should always be accompanied by a parallel investigation on blood samples collected at the time of the EMB. According to the recent Association for European Cardiovascular Pathology guidelines, optimal specimen procurement and triage indicates at least three, preferably four, EMB fragments, each 1-2 mm in size, that should immediately be fixed in 10 % buffered formalin at room temperature for light microscopic examination. In expected focal myocardial lesions, additional sampling is recommended. Moreover, one or two specimens should be snap-frozen in liquid nitrogen and stored at -80 °C or alternatively stored in RNA-later for possible molecular tests or specific stains. A sample of peripheral blood (5-10 ml) in EDTA or citrate from patients with suspected myocarditis allows molecular testing for the same viral genomes sought in the myocardial tissue.

2011 consensus statement on endomyocardial biopsy from the Association for European Cardiovascular Pathology and the Society for Cardiovascular Pathology

The Association for European Cardiovascular Pathology and the Society for Cardiovascular Pathology have produced this position paper concerning the current role of endomyocardial biopsy (EMB) for the diagnosis of cardiac diseases and its contribution to patient management, focusing on pathological issues, with these aims: • Determining appropriate EMB use in the context of current diagnostic strategies for cardiac diseases and providing recommendations for its rational utilization • Providing standard criteria and guidance for appropriate tissue triage and pathological analysis • Promoting a team approach to EMB use, integrating the competences of pathologists, clinicians, and imagers.

Pericarditis: pathophysiology, diagnosis, and management

Pericarditis, the most common disease of the pericardium, may be isolated or a manifestation of a systemic disease. The etiology of pericarditis is varied and includes infectious (especially viral and tuberculosis) and noninfectious causes (autoimmune and autoinflammatory diseases, pericardial injury syndromes, and cancer [especially lung cancer, breast cancer, and lymphomas]). Most cases remain idiopathic with a conventional diagnostic evaluation. A targeted etiologic search should be directed to the most common cause on the basis of the patient's clinical background, epidemiologic issues, specific presentations, and high-risk features associated with specific etiologies or complications (fever higher than 38°C, subacute onset, large pericardial effusion, cardiac tamponade, lack of response to NSAIDs). The management of pericardial diseases is largely empiric because of the relative lack of randomized trials. NSAIDs are the mainstay of empiric anti-inflammatory therapy, with the possible addition of colchicine to prevent recurrences.

Acute myocarditis in children

Myocarditis is an uncommon but significant disease in children. Diagnosis requires a high index of suspicion and understanding of the clinical presentation of this disease. The understanding of the mechanisms of disease-host immune response and host response has improved, but is not completely known. Therapy remains mainly supportive, while the use of immunotherapy in children is still controversial. The majority of children will improve; however, a substantial portion of children will die or develop persistent dilated cardiomyopathy leading to necessary heart transplantation.