Clinical and microbiological data and echocardiography findings
In total, 82 patients (mean age of 61 +/- 19 years, 62% of male gender) were enrolled from May 2016 to June 2019. Baseline characteristics were summarized in Table 1.
Half of included patients had an implanted prosthetic valve (n=35), the majority of which biological (n=19) and in aortic position (n=27).
Fever was present in most patients (n=64) (Table 2), followed by heart failure symptoms and vascular occurrences. One patient presented with pacemaker pocket signs of infection. Staphylococcus aureus was identified in 19 cases and more than half of these were methicillin resistant (52.9%). Presence of vegetations was the most common echocardiographic finding (n=31), followed by moderate to severe regurgitation (n=14), presence of abscess, pseudoaneurysm (n=9) or fistulae (n=5).
PET/CT findings
Seventy patients (90.9%) were under antibiotic therapy before PET/CT with a mean interval between treatment initiation and PET/ CT of 20±14 days. PET/CT was positive for IE in 24 cases. The receiver-operating characteristic curve yielded an area under the curve of 0.91 (95% confidence interval, 0.88–0.96) for SUVmax. A SUVmax cutoff value of ≥3.1 identified positive cases with 88.9%% sensitivity and 70.0% specificity (Figure 1).
PET/ CT performance in IE of NVE and PVE diagnosis
There were 6718F-FDG PET/CT concordant results with the final diagnosis of the endocarditis team, corresponding to a 96% of agreement, k = 0.91(p=0.04).
PET/CT was positive in 1 patient without a final diagnosis of IE (false positive, 2.2%). Conversely, PET/CT was negative in 4 patients with a diagnosis IE (false negative, 5.7%).
The sensitivity, specificity, positive, negative predictive values and area under the curve (95% confidence intervals) of DC at admission, echocardiogram and PET/CT in the diagnosis of IE are shown in Table 3.The addition of PET/CT to the modified DC resulted in a substantial increase in diagnostic specificity (from 33.3% to 97.8%) with only a mild reduction in sensitivity (from 88.0% to 84.0%). The percentage of IE cases classified as “possible” was reduced from 58% to 4.3%.
Concerning the subgroup of patients with intracardiac devices, PET/CT showed similar sensitivity to DC at admission but superior to echocardiography (89.5% vs 68.4%). PET/CT was also more specific than echocardiogram and DC at admission for diagnosis of device IE (90.0% vs 60.0% vs 51.0%). In this subgroup, PET/CT allowed reclassification, reducing from 67.4% of possible cases to 4.2 %. (Figure 4)
Extracardiac Findings: Additional Benefits of Whole-Body PET/CT
PET/CT detected 4 cases of peripheral embolism, which were asymptomatic. In addition, PET/CT identified clinical important extracardiac findings in 34 patients, and provided an alternative diagnosis in 22 of the negative IE cases: other infection foci in 13 patients [pneumonia (n=3), Q fever (n=5), colon abscess/diverticulitis (n=1), spondylodiscitis (n=5),hepatic abscess (n=2), phlebitis (n=1), sternotomy infection (n=1)]; 1 patient with Takayasu´s arteritis exacerbation and 8 unsuspected neoplastic lesions [colon (n=1), kidney (n=1), testicle (n=1) and lymphoma (n=5)], (figure 2-5).
Final Diagnosis and Patient Management
The patients were followed during a mean of 14 +/- 10months. According to diagnosis gold standard defined for this study, IE was established in 22 patients and was rejected in 45 patients; 3 patients were classified as possible IE. Those patients with definitive diagnosis of IE, 11 were submitted to surgery or percutaneous extraction of leads or devices. The remaining patients were medically managed. The all-cause mortality was 17.1% (12 patients).