Large Animal Translational Validation of 3 Mitral Valve Repair Operations for Mitral Regurgitation Using a Mitral Valve Prolapse Model: A Comprehensive In Vivo Biomechanical Engineering Analysis.

BACKGROUND: Various mitral repair techniques have been described. Though these repair techniques can be highly effective when performed correctly in suitable patients, limited quantitative biomechanical data are available. Validation and thorough biomechanical evaluation of these repair techniques from translational large animal in vivo studies in a standardized, translatable fashion are lacking. We sought to evaluate and validate biomechanical differences among different mitral repair techniques and further optimize repair operations using a large animal mitral valve prolapse model. METHODS: Male Dorset sheep (n=20) had P2 chordae severed to create the mitral valve prolapse model. Fiber Bragg grating force sensors were implanted to measure chordal forces. Ten sheep underwent 3 randomized, paired mitral valve repair operations: neochord repair, nonresectional leaflet remodeling, and triangular resection. The other 10 sheep underwent neochord repair with 2, 4, and 6 neochordae. Data were collected at baseline, mitral valve prolapse, and after each repair. RESULTS: All mitral repair techniques successfully eliminated regurgitation. Compared with mitral valve prolapse (0.54±0.18 N), repair using neochord (0.37±0.20 N; P=0.02) and remodeling techniques (0.30±0.15 N; P=0.001) reduced secondary chordae peak force. Neochord repair further decreased primary chordae peak force (0.21±0.14 N) to baseline levels (0.20±0.17 N; P=0.83), and was associated with lower primary chordae peak force compared with the remodeling (0.34±0.18 N; P=0.02) and triangular resectional techniques (0.36±0.27 N; P=0.03). Specifically, repair using 2 neochordae resulted in higher peak primary chordal forces (0.28±0.21 N) compared with those using 4 (0.22±0.16 N; P=0.02) or 6 neochordae (0.19±0.16 N; P=0.002). No difference in peak primary chordal forces was observed between 4 and 6 neochordae (P=0.05). Peak forces on the neochordae were the lowest using 6 neochordae (0.09±0.11 N) compared with those of 4 neochordae (0.15±0.14 N; P=0.01) and 2 neochordae (0.29±0.18 N; P=0.001). CONCLUSIONS: Significant biomechanical differences were observed underlying different mitral repair techniques in a translational large animal model. Neochord repair was associated with the lowest primary chordae peak force compared to the remodeling and triangular resectional techniques. Additionally, neochord repair using at least 4 neochordae was associated with lower chordal forces on the primary chordae and the neochordae. This study provided key insights about mitral valve repair optimization and may further improve repair durability.

Epizootic of enterocolitis and clostridial overgrowth in NSG and NSG-related mouse strains.

While the immunodeficient status of NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) and NSG-related mice provides utility for numerous research models, it also results in increased susceptibility to opportunistic pathogens. Over a 9-week period, a high rate of mortality was reported in a housing room of NSG and NSG-related mice. Diagnostics were performed to determine the underlying etiopathogenesis. Mice submitted for evaluation included those found deceased (n = 2), cage mates of deceased mice with or without diarrhea (n = 17), and moribund mice (n = 8). Grossly, mice exhibited small intestinal and cecal dilation with abundant gas and/or digesta (n = 18), serosal hemorrhage and congestion (n = 6), or were grossly normal (n = 3). Histologically, there was erosive to ulcerative enterocolitis (n = 7) of the distal small and large intestine or widespread individual epithelial cell death with luminal sloughing (n = 13) and varying degrees of submucosal edema and mucosal hyperplasia. Cecal dysbiosis, a reduction in typical filamentous bacteria coupled with overgrowth of bacterial rods, was identified in 18 of 24 (75%) mice. Clostridium spp. and Paeniclostridium sordellii were identified in 13 of 23 (57%) and 7 of 23 (30%) mice, respectively. Clostridium perfringens (7 of 23, 30%) was isolated most frequently. Toxinotyping of C. perfringens positive mice (n = 2) identified C. perfringens type A. Luminal immunoreactivity to several clostridial species was identified within lesioned small intestine by immunohistochemistry. Clinicopathologic findings were thus associated with overgrowth of various clostridial species, though direct causality could not be ascribed. A diet shift preceding the mortality event may have contributed to loss of intestinal homeostasis.

Efficacy of 3 Buprenorphine Formulations for the Attenuation of Hypersensitivity after Plantar Incision in Immunodeficient NSG Mice.

Buprenorphine is perhaps the most prescribed analgesic for management of postoperative pain in mice. Although various buprenorphine formulations are effective in commonly used immunocompetent mouse strains, a knowledge gap exists regarding its efficacy in immunodeficient mice. Here we used a plantar incision to evaluate the efficacy of 3 buprenorphine formulations for attenuating postoperative mechanical and thermal hypersensitivity in the immunodeficient NSG mouse strain. We also characterized the pharmacokinetics of these formulations over a 72-h period. We hypothesized that all 3 buprenorphine formulations evaluated-the standard preparation and 2 extended-release products (Bup-HCl, Bup-ER, and Bup-XR, respectively)-would attenuate postoperative mechanical and thermal hypersensitivity resulting from a plantar incision in NSG mice. Male and female NSG mice (n = 48) were allocated to 4 treatment groups: saline (0.9% NaCl, 5 mL/kg SC once); Bup-HCl (0.1 mg/kg SC, BID for 2 d); Bup-ER (1.0 mg/kg SC once); and Bup-XR (3.25 mg/kg SC once). Mechani- cal and thermal hypersensitivity assessments were conducted 24 h before surgery and at 4, 8, 24, 48, and 72 h afterward. All groups of mice showed mechanical and thermal hypersensitivity within the first 24 h after surgery. Behavioral pain indicators (guarding, toe-touching [intermittent partial weight bearing], licking the incision, vocalizations) were observed in some mice from each group at every postoperative time point. Plasma buprenorphine was measured in a separate group of mice and concentrations surpassed the suggested therapeutic level (1.0 ng/mL) for less than 4 h for Bup-HCl, for at least 24 h for Bup-ER, and for 72 h for Bup-XR. Our results indicate that at the dosages studied, these buprenorphine formulations do not adequately attenuate postoperative mechanical and thermal hypersensitivity in the plantar incisional model in NSG mice. These findings support the need for strain-specific analgesic protocols for mice used in research.