Cardiac arrhythmias are associated with cardiovascular morbidity and mortality. Cardiac electrophysiology studies (EPS) use intracardiac catheter recording and stimulation for profound evaluation of the heart's electrical properties. The main clinical application is investigation and treatment of rhythm disorders. These techniques have been translated to the murine setting to open opportunities for detailed evaluation of the impact of different characteristics (including genetics) and interventions on cardiac electrophysiology and -pathology. Currently, a detailed description of the technique of murine transjugular EPS (which is the standard route of catheter introduction) is lacking. This article provides detailed information on EPS in mice via the transjugular route. This includes catheter placement, stimulation protocols, intracardiac tracing interpretation, artefact reduction and surface ECG recording. In addition, reference values as obtained in C57BL/6N mice are presented for common electrophysiological parameters. This detailed methodological description aims to increase accessibility and standardisation of EPS in mice. Ultimately, also human research and patient care may benefit from translation of the knowledge obtained in preclinical models using this technique.

Unprecedented immunization campaigns have been rolled out worldwide in an attempt to contain the ongoing COVID-19 pandemic. Multiple vaccines were brought to the market, among two utilizing novel messenger ribonucleic acid technology. Despite their undisputed success in decreasing COVID-19-associated hospitalizations and mortality, various adverse events have been reported. The emergence of malignant lymphoma is one of such rare adverse events that has raised concern, although an understanding of the mechanisms potentially involved remains lacking. Herein, we present the first case of B-cell lymphoblastic lymphoma following intravenous high-dose mRNA COVID-19 vaccination (BNT162b2) in a BALB/c mouse. Two days following booster vaccination (i.e., 16 days after prime), at only 14 weeks of age, our animal suffered spontaneous death with marked organomegaly and diffuse malignant infiltration of multiple extranodal organs (heart, lung, liver, kidney, spleen) by lymphoid neoplasm. Immunohistochemical examination revealed organ sections positive for CD19, terminal deoxynucleotidyl transferase, and c-MYC, compatible with a B-cell lymphoblastic lymphoma immunophenotype. Our murine case adds to previous clinical reports on malignant lymphoma development following novel mRNA COVID-19 vaccination, although a demonstration of direct causality remains difficult. Extra vigilance is required, with conscientious reporting of similar cases and a further investigation of the mechanisms of action explaining the aforementioned association.

Background and Aims The goal of the present study was to systematically evaluate the effect of a booster vaccination with the BNT162b2 messenger RNA (mRNA; Pfizer‐BioNTech®) vaccine on maximum oxygen uptake (VO 2 max ), potential signs of (peri)myocarditis, and sports participation. Methods Recreational athletes who were scheduled to undergo booster vaccination were evaluated with transthoracic echocardiography, serum measurements of high‐sensitivity C‐reactive protein(hsCRP) and high‐sensitivity troponin I, and a bicycle cardiopulmonary exercise test (CPET) with serum lactate evaluation before the booster vaccine administration. Seven days postvaccination the test battery was repeated. Additionally, the subjects were asked to fill in a questionnaire on side effects and a subjective evaluation of their relative training volume and intensity as compared to the weeks before vaccination. Results A group of 42 analysed athletes showed a statistically significant 2.7% decrease in VO 2 max after vaccination (mean standard error of mean pre: 48.6 (1.4) ml/kg/min; post: 47.3 (1.4) ml/kg/min; p = 0.004). A potentially clinically relevant decrease of 8.6% or more occurred in 8 (19%) athletes. Other CPET parameters and lactate curves were comparable. We found no serological or echocardiographic evidence of (peri)myocarditis. A slight but significant increase in hsCRP was noted 1 week after vaccination. Side effects were mild and sports participation was generally unchanged or mildly decreased after vaccination. Conclusion In our population of recreational endurance athletes, booster vaccination with the BNT162b2 mRNA vaccine resulted in a statistically significant decrease in VO 2max 7 days after vaccination. The clinical impact hereof needs to be further determined. No major adverse events were observed.

Background: Allylnitrile is a compound found in cruciferous vegetables and has the same lethality and toxic effects as the other nitriles. In 2013, a viable allylnitrile ototoxicity mouse model was established. The toxicity of allylnitrile was limited through inhibition of CYP2E1 with trans-1,2-dichloroethylene (TDCE). The allylnitrile intoxication model has been extensively tested in the 129S1 mouse strain for vestibular function, which showed significant HC loss in the vestibular organ accompanied by severe behavioral abnormalities. However, the effect of allylnitrile on auditory function remains to be evaluated. Commonly used anesthetics to conduct hearing measurements are isoflurane and ketamine/xylazine anesthesia but the effect of these anesthetics on hearing assessment is still unknown. In this study we will evaluate the otovestibular effects of oral allylnitrile administration in mice. In addition, we will compare the influence of isoflurane and ketamine/xylazine anesthesia on hearing thresholds.Methods and Materials: Fourteen Coch+/– CBACa mice were randomly allocated into an allylnitrile (n = 8) and a control group (n = 6). Baseline measurements were done with isoflurane and 1 week later under ketamine/xylazine anesthesia. After baseline audiovestibular measurements, mice were co-administered with a single dose of allylnitrile and, to reduce systemic toxicity, three intraperitoneal injections of TDCE were given. Hearing loss was evaluated by recordings of auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE). Specific behavioral test batteries for vestibular function were used to assess alterations in vestibular function.Results: Hearing thresholds were significantly elevated when using isoflurane anesthesia compared to ketamine/xylazine anesthesia for all frequencies of the ABR and the mid-to-high frequencies in DPOAE. Allylnitrile-treated mice lacked detectable ABR thresholds at each frequency tested, while DPOAE thresholds were significantly elevated in the low-frequency region of the cochlea and completely lacking in the mid-to high frequency region. Vestibular function was not affected by allylnitrile administration.Conclusion: Isoflurane anesthesia has a negative confounding effect on the measurement of hearing thresholds in mice. A single oral dose of allylnitrile induced hearing loss but did not significantly alter vestibular function in mice. This is the first study to show that administration of allylnitrile can cause a complete loss of hearing function in mice.

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation Flanders Introduction Myocarditis is an inflammatory disease of the heart with viral infections being the most common aetiology. Often, myocardial fibrosis (MF) is observed during the resolution of myocarditis. MF is a strong independent predictor for outcome in patients with myocarditis. Nevertheless, the late stages of disease, encompassing fibrogenesis and arrhythmogenesis, have been underappreciated in viral myocarditis research to date. Purpose The primary aim of this study was to characterise the natural history of coxsackievirus B3 (CVB3)-induced myocarditis in C57BL/6J mice, with emphasis on fibrogenesis and its electrical impact. Secondary aims were 1) to study the impact of inoculation dose and sex on the course of disease, and 2) to develop an in-house histopathological scoring system for inflammation and fibrosis. Methods C57BL/6J mice (12 weeks old; n=154) received intraperitoneal injection with CVB3 (Nancy strain). Male mice received 5 x 10^5 (regular dose)(RD) or 5 x 10^6 (high dose) plaque-forming units, whereas female mice received the RD only. Mice injected with PBS served as control groups. Animals were sacrificed 7, 14, 28, 56 and 77 days after CVB3 or PBS injection. Inflammation (haematoxylin-eosin) and fibrosis (Picrosirius red (PSR)) were evaluated histologically. Arrhythmogenicity was assessed through right ventricular programmed stimulation. Results CVB3 animals sacrificed or with spontaneous death within 14 days after inoculation showed cardiac infiltration in all (100%) and necrosis in 88% (35/40). In male CVB3-infected mice, premature mortality was ±20% in both regular and high dose groups, occurring between 9 and 23 days post inoculation. No mortality was observed in the female group (p<0.025 for comparison male and female RD). Cardiac inflammation had resolved in the majority of animals at day 77. Perivascular fibrosis was seen in both infected and control mice. Pericellular fibrosis and organised scarring were seen in CVB3-infected animals only, and mainly became evident 56 and 77 days after inoculation (51% of infected animals). Also total cross-sectional PSR-positive area was 2-3-fold higher in CVB-infected mice compared to sex-matched controls, independent of inoculation dose (p<0.05). At the 56- and 77-day timepoint, nonsustained ventricular tachycardia was induced in 17% (5/29) of the intervention animals (all with pericellular fibrosis or scarring) and none (0/14) of the control animals, but this did not reach statistical significance (p=0.098). Conclusion We report on the characterisation of fibrotic remodelling in a CVB3-induced myocarditis mouse model. Fibrotic remodelling was seen in a majority of mice after 8 to 11 weeks. It was associated with a numerical (but not significant) increased arrhythmogenicity, requiring further exploration given the clinical significance of fibrotic remodelling. Further research on the molecular pathways and cellular interactions triggered by myocarditis is ongoing.