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Utility of Cardiac Magnetic Resonance Imaging in Predicting Atrial Arrhythmias in Repaired Tetralogy of Fallot.

Arrhythmias are the leading cause of morbidity and mortality in repaired tetralogy of Fallot (TOF), and over 20% of these patients will develop a sustained atrial arrhythmia during their lifetimes. Cardiac magnetic resonance imaging (cMRI) is frequently performed in TOF, although its ability to identify patients at risk of atrial arrhythmias is uncertain. Adult TOF patients (n = 175) with no history of atrial arrhythmia who underwent cMRI between 2003 and 2020 at a single tertiary care center were identified. Clinical characteristics and imaging findings were evaluated to identify a predilection for atrial arrhythmias using Kaplan-Meier survival analysis and log-rank testing. Multivariable Cox regression was used to determine independent predictors of atrial arrhythmias. Over a median follow-up of 3.6 years, 29 patients (17%) developed atrial arrhythmias. Independent predictors of atrial arrhythmia included age (hazard ratio [HR] 1.06 per 1-year increase, 95% confidence interval [CI] 1.02 to 1.09, p = 0.002), diabetes mellitus (HR 4.26, 95% CI 1.26 to 14.41, p = 0.020), indexed right ventricular end-diastolic volume (RVEDVi), (HR 1.20 per 10-ml/m2 increase, 95% CI 1.05 to 1.39, p = 0.010), and moderate or greater tricuspid regurgitation (TR) (HR 6.32, 95% CI 2.15 to 18.60, p = 0.001). Utilizing Kaplan-Meier analysis, patients with at least mild right ventricular dilation (RVEDVi >100 ml/m2, p = 0.047) and greater than or equal to moderate TR (p <0.001) were found to be significantly more likely to develop atrial arrhythmias. In conclusion, cMRI can help to identify TOF patients at increased risk for atrial arrhythmia beyond standard clinical and imaging data by better quantifying RVEDVi and degree of TR.

Burden and Impact of Arrhythmias in Repaired Tetralogy of Fallot.

PURPOSE OF REVIEW: Arrhythmias are a leading cause of morbidity and mortality following repair of tetralogy of Fallot (TOF). This review will highlight current understanding of arrhythmia pathogenesis in this patient population and review novel therapeutic options. RECENT FINDINGS: Risk factors for developing ventricular arrhythmias in repaired TOF have thus far been better defined than for atrial arrhythmias. Growing understanding of the pathophysiology of arrhythmias, development of risk stratification models, and novel techniques such as electrophysiologic ultrahigh-density mapping should help to better identify patients that benefit from advanced therapies such as ablation and implantable cardioverter defibrillators. Atrial and ventricular arrhythmias are common in TOF patients. Methods of risk stratification and therapeutic approaches are rapidly evolving, leading to ever improving clinical outcomes in this patient population.

Development of a Staphylococcus aureus reporter strain with click beetle red luciferase for enhanced in vivo imaging of experimental bacteremia and mixed infections.

In vivo bioluminescence imaging has been used to monitor Staphylococcus aureus infections in preclinical models by employing bacterial reporter strains possessing a modified lux operon from Photorhabdus luminescens. However, the relatively short emission wavelength of lux (peak 490 nm) has limited tissue penetration. To overcome this limitation, the gene for the click beetle (Pyrophorus plagiophtalamus) red luciferase (luc) (with a longer >600 emission wavelength), was introduced singly and in combination with the lux operon into a methicillin-resistant S. aureus strain. After administration of the substrate D-luciferin, the luc bioluminescent signal was substantially greater than the lux signal in vitro. The luc signal had enhanced tissue penetration and improved anatomical co-registration with infected internal organs compared with the lux signal in a mouse model of S. aureus bacteremia with a sensitivity of approximately 3 × 104 CFU from the kidneys. Finally, in an in vivo mixed bacterial wound infection mouse model, S. aureus luc signals could be spectrally unmixed from Pseudomonas aeruginosa lux signals to noninvasively monitor the bacterial burden of both strains. Therefore, the S. aureus luc reporter may provide a technological advance for monitoring invasive organ dissemination during S. aureus bacteremia and for studying bacterial dynamics during mixed infections.

Efficacy of a Multimechanistic Monoclonal Antibody Combination against Staphylococcus aureus Surgical Site Infections in Mice.

Surgical site infections (SSIs) are commonly caused by Staphylococcus aureus We report that a combination of three monoclonal antibodies (MEDI6389) that neutralize S. aureus alpha-toxin, clumping factor A, and four leukocidins (LukSF, LukED, HlgAB, and HlgCB) plus vancomycin had enhanced efficacy compared with control antibody plus vancomycin in two mouse models of S. aureus SSI. Therefore, monoclonal antibody-based neutralization of multiple S. aureus virulence factors may provide an adjunctive perioperative approach to combat S. aureus SSIs.

Clonal Vγ6+Vδ4+ T cells promote IL-17-mediated immunity against Staphylococcus aureus skin infection.

T cell cytokines contribute to immunity against Staphylococcus aureus, but the predominant T cell subsets involved are unclear. In an S. aureus skin infection mouse model, we found that the IL-17 response was mediated by γδ T cells, which trafficked from lymph nodes to the infected skin to induce neutrophil recruitment, proinflammatory cytokines IL-1α, IL-1ß, and TNF, and host defense peptides. RNA-seq for TRG and TRD sequences in lymph nodes and skin revealed a single clonotypic expansion of the encoded complementarity-determining region 3 amino acid sequence, which could be generated by canonical nucleotide sequences of TRGV5 or TRGV6 and TRDV4 However, only TRGV6 and TRDV4 but not TRGV5 sequences expanded. Finally, Vγ6+ T cells were a predominant γδ T cell subset that produced IL-17A as well as IL-22, TNF, and IFNγ, indicating a broad and substantial role for clonal Vγ6+Vδ4+ T cells in immunity against S. aureus skin infections.

Theranostic biocomposite scaffold membrane.

Acute and chronic wounds affect millions and are associated with billions of dollars in healthcare costs. The use of healing markers, biochemical cues from biocompatible matrices and materials, and their correlation with wound healing has the potential to generate valuable diagnostic, prognostic, and therapeutic information. In this study, we developed a collagen-dextran oxygen-sensing biocomposite scaffold membrane in which a phosphorescent oxygen sensor was incorporated to monitor physiological oxygen using in vivo phosphorescence imaging in a preclinical mouse model of wound healing. The oxygen-sensing biocomposite scaffold membrane enabled the noninvasive and longitudinal monitoring of oxygenation changes in vivo in an approach compatible with commercially available preclinical in vivo imaging system instruments. This study provides a new and novel capability where a biocomposite material can serve as a biocompatible, biodegradable theranostic platform to promote and assess tissue oxygenation during wound healing.

In Vivo Bioluminescence Imaging in a Rabbit Model of Orthopaedic Implant-Associated Infection to Monitor Efficacy of an Antibiotic-Releasing Coating.

BACKGROUND: In vivo bioluminescence imaging (BLI) provides noninvasive monitoring of bacterial burden in animal models of orthopaedic implant-associated infection (OIAI). However, technical limitations have limited its use to mouse and rat models of OIAI. The goal of this study was to develop a larger, rabbit model of OIAI using in vivo BLI to evaluate the efficacy of an antibiotic-releasing implant coating. METHODS: A nanofiber coating loaded with or without linezolid-rifampin was electrospun onto a surgical-grade locking peg. To model OIAI in rabbits, a medial parapatellar arthrotomy was performed to ream the femoral canal, and a bright bioluminescent methicillin-resistant Staphylococcus aureus (MRSA) strain was inoculated into the canal, followed by retrograde insertion of the coated implant flush with the articular surface. In vivo BLI signals were confirmed by ex vivo colony-forming units (CFUs) from tissue, bone, and implant specimens. RESULTS: In this rabbit model of OIAI (n = 6 rabbits per group), implants coated without antibiotics were associated with significantly increased knee width and in vivo BLI signals compared with implants coated with linezolid-rifampin (p < 0.001 and p < 0.05, respectively). On day 7, the implants without antibiotics were associated with significantly increased CFUs from tissue (mean [and standard error of the mean], 1.4 × 10 ± 2.1 × 10 CFUs; p < 0.001), bone (6.9 × 10 ± 3.1 × 10 CFUs; p < 0.05), and implant (5.1 × 10 ± 2.2 × 10 CFUs; p < 0.05) specimens compared with implants with linezolid-rifampin, which demonstrated no detectable CFUs from any source. CONCLUSIONS: By combining a bright bioluminescent MRSA strain with modified techniques, in vivo BLI in a rabbit model of OIAI demonstrated the efficacy of an antibiotic-releasing coating. CLINICAL RELEVANCE: The new capability of in vivo BLI for noninvasive monitoring of bacterial burden in larger-animal models of OIAI may have important preclinical relevance.

Clonally expanded γδ T cells protect against Staphylococcus aureus skin reinfection.

The mechanisms that mediate durable protection against Staphylococcus aureus skin reinfections are unclear, as recurrences are common despite high antibody titers and memory T cells. Here, we developed a mouse model of S. aureus skin reinfection to investigate protective memory responses. In contrast with WT mice, IL-1ß-deficient mice exhibited poor neutrophil recruitment and bacterial clearance during primary infection that was rescued during secondary S. aureus challenge. The γδ T cells from skin-draining LNs utilized compensatory T cell-intrinsic TLR2/MyD88 signaling to mediate rescue by trafficking and producing TNF and IFN-γ, which restored neutrophil recruitment and promoted bacterial clearance. RNA-sequencing (RNA-seq) of the LNs revealed a clonotypic S. aureus-induced γδ T cell expansion with a complementarity-determining region 3 (CDR3) aa sequence identical to that of invariant Vγ5+ dendritic epidermal T cells. However, this T cell receptor γ (TRG) aa sequence of the dominant CDR3 sequence was generated from multiple gene rearrangements of TRGV5 and TRGV6, indicating clonotypic expansion. TNF- and IFN-γ-producing γδ T cells were also expanded in peripheral blood of IRAK4-deficient humans no longer predisposed to S. aureus skin infections. Thus, clonally expanded γδ T cells represent a mechanism for long-lasting immunity against recurrent S. aureus skin infections.

Neutralizing Alpha-Toxin Accelerates Healing of Staphylococcus aureus-Infected Wounds in Nondiabetic and Diabetic Mice.

Staphylococcus aureus wound infections delay healing and result in invasive complications such as osteomyelitis, especially in the setting of diabetic foot ulcers. In preclinical animal models of S. aureus skin infection, antibody neutralization of alpha-toxin (AT), an S. aureus-secreted pore-forming cytolytic toxin, reduces disease severity by inhibiting skin necrosis and restoring effective host immune responses. However, whether therapeutic neutralization of alpha-toxin is effective against S. aureus-infected wounds is unclear. Herein, the efficacy of prophylactic treatment with a human neutralizing anti-AT monoclonal antibody (MAb) was evaluated in an S. aureus skin wound infection model in nondiabetic and diabetic mice. In both nondiabetic and diabetic mice, anti-AT MAb treatment decreased wound size and bacterial burden and enhanced reepithelialization and wound resolution compared to control MAb treatment. Anti-AT MAb had distinctive effects on the host immune response, including decreased neutrophil and increased monocyte and macrophage infiltrates in nondiabetic mice and decreased neutrophil extracellular traps (NETs) in diabetic mice. Similar therapeutic efficacy was achieved with an active vaccine targeting AT. Taken together, neutralization of AT had a therapeutic effect against S. aureus-infected wounds in both nondiabetic and diabetic mice that was associated with differential effects on the host immune response.