Left Ventricular Strain from Myocardial Perfusion PET Imaging: Method Development and Comparison to 2-Dimensional Echocardiography.

This study aimed to develop a measure of longitudinal, radial, and circumferential myocardial strain at rest and regadenoson during pharmacologic stress using 82Rb PET electrocardiography-gated myocardial perfusion imaging (MPI). Methods: We retrospectively identified 80 patients who underwent rest and regadenoson-stress CT attenuation-corrected 82Rb PET and had a standard resting transthoracic echocardiogram (TTE) with global longitudinal strain (GLS) analysis within 3 mo. A method was developed to compute longitudinal, radial, and circumferential strain from PET MPI at stress and rest. PET MPI-derived strain and left ventricular function were compared with resting TTE measures as the clinical reference standard. Interobserver agreement of PET MPI strain and left ventricular ejection fraction processing was reported. Results: Longitudinal strain assessed with resting TTE GLS showed good correlation with PET MPI at stress (r = 0.68, P < 0.001) and rest (r = 0.58, P < 0.001). Resting TTE GLS also correlated with PET MPI radial strain at stress (r = -0.70, P < 0.001) and rest (r = -0.59, P < 0.001) and circumferential strain at stress (r = 0.67, P < 0.001) and rest (r = 0.69, P < 0.001). The left ventricular ejection fraction showed good correlation between resting TTE and PET MPI at stress (r = 0.83, P < 0.001) and rest (r = 0.80, P < 0.001). Bland-Altman analysis indicated positive bias of TTE GLS compared with PET MPI longitudinal strain at stress (mean difference = 5.1%, 95% CI = [-2.5, 12.7]) and rest (mean difference = 4.2%, 95% CI = [-4.3, 12.8]). Reproducibility of PET MPI longitudinal strain showed good agreement at stress (concordance correlation coefficient = 0.73, P < 0.001) and rest (concordance correlation coefficient = 0.74, P < 0.001), with Bland-Altman analysis showing a small bias in the longitudinal direction at stress (mean difference = -0.2%) and rest (mean difference = -1.0%). Conclusion: Strain measured with PET MPI using an automated technique correlated well with resting GLS strain obtained by TTE, and the measure is reproducible. Strain from PET MPI should be investigated further to establish reference ranges and assess its value in routine clinical practice.

Risk Factors Associated With New-Onset Myocardial Perfusion Abnormalities in Kidney Transplant Candidates.

The optimal coronary artery disease surveillance strategy for end-stage renal disease patients being evaluated for kidney transplantation is unknown. It is unclear what risk factors are associated with the development of new-onset perfusion abnormalities on serial myocardial perfusion imaging. Potential kidney transplant recipients who underwent 2 myocardial perfusion imaging studies at Emory University Hospital between January 2010 and December 2019 were identified. We assessed the frequency of development of any new perfusion defect and development of moderate to severe ischemia (reversible perfusion defect >10%) on serial imaging. Finally, we identified the clinical and imaging factors associated with new perfusion defects and explored the association between new perfusion defects and all-cause mortality. History of myocardial infarction (MI) and peripheral artery disease was associated with an increased risk of developing a new perfusion defect. History of MI was also associated with the risk of developing moderate-severe ischemia. Female patients were less likely to develop new perfusion defects or moderate-severe ischemia. There was no association between either outcome and all-cause mortality. In conclusion, a history of MI, peripheral artery disease, and male gender are risk factors for developing new perfusion defects, although only the history of MI and male gender predict moderate to severe ischemia. Interval development of any abnormal perfusion is not associated with increased mortality.

Pleomorphic Structures in Human Blood Are Red Blood Cell-Derived Microparticles, Not Bacteria.

BACKGROUND: Red blood cell (RBC) transfusions are a common, life-saving therapy for many patients, but they have also been associated with poor clinical outcomes. We identified unusual, pleomorphic structures in human RBC transfusion units by negative-stain electron microscopy that appeared identical to those previously reported to be bacteria in healthy human blood samples. The presence of viable, replicating bacteria in stored blood could explain poor outcomes in transfusion recipients and have major implications for transfusion medicine. Here, we investigated the possibility that these structures were bacteria. RESULTS: Flow cytometry, miRNA analysis, protein analysis, and additional electron microscopy studies strongly indicated that the pleomorphic structures in the supernatant of stored RBCs were RBC-derived microparticles (RMPs). Bacterial 16S rDNA PCR amplified from these samples were sequenced and was found to be highly similar to species that are known to commonly contaminate laboratory reagents. CONCLUSIONS: These studies suggest that pleomorphic structures identified in human blood are RMPs and not bacteria, and they provide an example in which laboratory contaminants may can mislead investigators.

Platelets confound the measurement of extracellular miRNA in archived plasma.

Extracellular miRNAs are detectable in biofluids and represent a novel class of disease biomarker. Although many studies have utilized archived plasma for miRNA biomarker discovery, the effects of processing and storage have not been rigorously studied. Previous reports have suggested plasma samples are commonly contaminated by platelets, significantly confounding the measurement of extracellular miRNA, which was thought to be easily addressed by additional post-thaw plasma processing. In a case-control study of archived plasma, we noted a significant correlation between miRNA levels and platelet counts despite post-thaw processing. We thus examined the effects of a single freeze/thaw cycle on microparticles (MPs) and miRNA levels, and show that a single freeze/thaw cycle of plasma dramatically increases the number of platelet-derived MPs, contaminates the extracellular miRNA pool, and profoundly affects the levels of miRNAs detected. The measurement of extracellular miRNAs in archived samples is critically dependent on the removal of residual platelets prior to freezing plasma samples. Many previous clinical studies of extracellular miRNA in archived plasma should be interpreted with caution and future studies should avoid the effects of platelet contamination.

An accurate, precise method for general labeling of extracellular vesicles.

Extracellular, membrane vesicles (microvesicles, exosomes) are secreted by cells and may serve as mediators of intercellular communication. Methods for detecting them by flow cytometry have included the use of agents that fluorescently stain vesicle membrane, or fluorescent antibodies that target specific cell-of-origin antigens. However, these methods may falsely detect cell debris or require prior cell-of-origin knowledge. Here, we demonstrate the suitability of calcein AM for detection of intact extracellular vesicles (EVs) by flow cytometry.•Calcein AM is non-fluorescent until it passively enters EVs, after which it is activated and becomes fluorescent and EV-impermeant.•Permeabilized/lysed EVs label positive with antibodies and lipophilic membrane stain, whereas no labeling was observed with calcein. In contrast to methods that use antibodies or membrane stains, calcein AM allows for the differentiation between intact EVs and debris.•Calcein AM can be used for detection of intact EVs from numerous cell types.