Polymerase Chain Reaction to Diagnose Infective Endocarditis

report on a series of 52 excised heart valves on which they performed broad-range polymerase chain reaction (PCR) to identify microbes in valve tissues that were defined as having infective endocarditis (IE). Internal sequencing of amplicons, with specific “nested” primers to identify microbial subspecies, was performed after broad-range PCR. The authors report that on the basis of gross features and histopathology, 22 (42.3%) of the 52 valves, which otherwise had evidence of IE, also had microbial subspecies identified. Eight (44%) of 18 IE valves that were preceded by positive blood cultures, where blood culture data were available, were positive by broad-range PCR. von Reyn’s,2 Duke,3 and modified Duke4 criteria use blood cultures as a major clinical criterion to predict IE and histopathologic evidence of IE on cardiac valves as “definite” evidence of IE. Arguably, these two criteria together represent the most definite evidence of disease. Therefore, it may seem enigmatic that between and among major criteria used for the diagnosis of IE, 50% of the valves in the Breitkopf et al series1 did not yield a causative microorganism identified by broad-range PCR. At first glance, broad-range PCR may seem to be a highly sensitive method to detect the presence of microbes. Indeed, this method was 3-fold more sensitive than the Gram stains and cultures performed on these tissues combined.