Effects of long-term exercise on arrhythmogenesis in aged hypertensive rats

Biomaterial-induced conversion of quiescent cardiomyocytes into pacemaker cells in rats

Pacemaker cells can be differentiated from stem cells or transdifferentiated from quiescent mature cardiac cells via genetic manipulation. Here we show that the exposure of rat quiescent ventricular cardiomyocytes to a silk-fibroin hydrogel activates the direct conversion of the quiescent cardiomyocytes to pacemaker cardiomyocytes by inducing the ectopic expression of the vascular endothelial cell-adhesion glycoprotein cadherin. The silk-fibroin-induced pacemaker cells exhibited functional and morphological features of genuine sinoatrial-node cardiomyocytes in vitro, and pacemaker cells generated via the injection of silk fibroin in the left ventricles of rats functioned as a surrogate in situ sinoatrial node. Biomaterials with suitable surface structure, mechanics and biochemistry could facilitate the scalable production of biological pacemakers for human use.

A genome-wide circular RNA transcriptome in rat

Circular RNAs (circRNAs) are a novel class of noncoding RNAs that back-splice from 5ʹ donor site and 3ʹ acceptor sites to form a circular structure. A number of circRNAs have been discovered in model organisms including human, mouse, Drosophila, among other organisms. There are a few candidate-based studies on circRNAs in rat, a well-studied model organism as well. A number of pipelines have been published to identify the back splice junctions for the discovery of circRNAs but studies comparing these tools have suggested that a combination of tools would be a better approach to identify high-confidence circRNAs. The availability of a recent dataset of transcriptomes encompassing 11 tissues, 4 developmental stages, and 2 genders motivated us to explore the landscape of circRNAs in the organism in this context. In order to understand the difference among different pipelines, we employed five different combinations of tools to identify circular RNAs from the dataset. We compared the results of the different combination of tools/pipelines with respect to alignment, total number of circRNAs identified and read-coverage. In addition, we identified tissue-specific, development-stage specific and gender-specific circRNAs and further independently validated 16 circRNA junctions out of 24 selected candidates in 5 tissue samples and estimated the quantitative expression of five circRNA candidates using real-time polymerase chain reaction and our analysis suggests three candidates as tissue-enriched. This study is one of the most comprehensive studies which provides a map of circRNAs transcriptome as well as to understand the difference among different computational pipelines in rat.

Effects of high-frequency biphasic shocks on ventricular vulnerability and defibrillation outcomes through synchronized virtual electrode responses

Electrical defibrillation is a well-established treatment for cardiac dysrhythmias. Studies have suggested that shock-induced spatial sawtooth patterns and virtual electrodes are responsible for defibrillation efficacy. We hypothesize that high-frequency shocks enhance defibrillation efficacy by generating temporal sawtooth patterns and using rapid virtual electrodes synchronized with shock frequency. High-speed optical mapping was performed on isolated rat hearts at 2000 frames/s. Two defibrillation electrodes were placed on opposite sides of the ventricles. An S1-S2 pacing protocol was used to induce ventricular tachyarrhythmia (VTA). High-frequency shocks of equal energy but varying frequencies of 125–1000 Hz were used to evaluate VTA vulnerability and defibrillation success rate. The 1000-Hz shock had the highest VTA induction rate in the shorter S1-S2 intervals (50 and 100 ms) and the highest VTA defibrillation rate (70%) among all frequencies. Temporal sawtooth patterns and synchronous shock-induced virtual electrode responses could be observed with frequencies of up to 1000 Hz. The improved defibrillation outcome with high-frequency shocks suggests a lower energy requirement than that of low-frequency shocks for successful ventricular defibrillation.

Rotenone and 3-bromopyruvate toxicity impacts electrical and structural cardiac remodeling in rats

3-Bromopyruvate (3-BrPA) is a promising agent that has been widely studied in the treatment of cancer and pulmonary hypertension. Rotenone is a pesticide commonly used on farms and was shown to have anti-cancer activity and delay fibrosis progression in chronic kidney disease in a recent study. However, there are few studies showing the toxicity of rotenone and 3-BrPA in the myocardium. To support further medical exploration, it is necessary to clarify the side effects of these compounds on the heart. This study was designed to examine the cardiotoxicity of 3-BrPA and rotenone by investigating electrical and structural cardiac remodeling in rats. Forty male rats were divided into 4 groups (n = 10 in each group) and injected intraperitoneally with 3-BrPA, rotenone or a combination of 3-BrPA and rotenone. The ventricular effective refractory period (VERP), corrected QT interval (QTc), and ventricular tachycardia/ventricular fibrillation (VT/VF) inducibility were measured. The expression of Cx43, Kir2.1, Kir6.2, DHPRα₁, KCNH2, caspase3, caspase9, Bax, Bcl2, and P53 was detected. Masson's trichrome, TUNEL, HE, and PAS staining and transmission electron microscopy were used to detect pathological and ultrastructural changes. Our results showed that rotenone alone and rotenone combined with 3-BrPA significantly increased the risk of ventricular arrhythmias. Rotenone combined with 3-BrPA caused myocardial apoptosis, and rotenone alone and rotenone combined with 3-BrPA caused electrical and structural cardiac remodeling in rats.

Prognostic Impact of Angiotensin-Converting Enzyme Inhibitors and Receptor Blockers on Recurrent Ventricular Tachyarrhythmias and Implantable Cardioverter-Defibrillator Therapies

This study sought to assess the prognostic impact of treatment with angiotensin-converting enzyme inhibitors (ACEi) or angiotensin receptor blockers (ARB) on recurrences of ventricular tachyarrhythmias in recipients of implantable cardioverter-defibrillators (ICD). Using a large retrospective registry including consecutive ICD recipients with documented episodes of ventricular tachycardia (VT) or fibrillation (VF) from 2002 to 2016, those patients treated with ACEi/ARB were compared with patients without. The primary prognostic endpoint was the first recurrence of ventricular tachyarrhythmias and related ICD therapies at 5 years. Multivariable Cox regression analyses were applied within the entire cohort, and thereafter, Kaplan-Meier analyses were performed in propensity-matched subgroups. A total of 592 consecutive ICD recipients were included (81% treated with ACEi/ARB and 19% without). Although ACEi/ARB was associated with no differences in overall recurrence of ventricular tachyarrhythmias, ACEi/ARB was associated with improved freedom from appropriate ICD therapy within multivariable Cox regressions (hazard ratio = 0.666; P = 0.043), especially in patients with index episodes of VF, left ventricular ejection fraction <35%, coronary artery disease, secondary preventive ICD, and glomerular filtration rate <45 mL/min/1.73 m. In the propensity-matched subgroup, ACEi/ARB still prolonged freedom from appropriate ICD therapies (hazard ratio = 0.380; 95% confidence interval 0.193-0.747; P = 0.005). In conclusion, ACEi/ARB therapy was associated with improved freedom from appropriate ICD therapies.

A systematic comparison of exercise training protocols on animal models of cardiovascular capacity

Cardiovascular disease (CVD) is a major global cause of mortality, which has prompted numerous studies seeking to reduce the risk of heart failure and sudden cardiac death. While regular physical activity is known to improve CVD associated morbidity and mortality, the optimal duration, frequency, and intensity of exercise remains unclear. To address this uncertainty, various animal models have been used to study the cardioprotective effects of exercise and related molecular mechanism such as the mice training models significantly decrease size of myocardial infarct by affecting Kir6.1, VSMC sarc-K_ATP channels, and pulmonary eNOS. Although these findings cement the importance of animal models in studying exercise induced cardioprotection, the vast assortment of exercise protocols makes comparison across studies difficult. To address this issue, we review and break down the existent exercise models into categories based on exercise modality, intensity, frequency, and duration. The timing of sample collection is also compared and sorted into four distinct phases: pre-exercise (Phase I), mid-exercise (Phase II), exercise recovery (Phase III), and post-exercise (Phase IV). Finally, because the life-span of animals so are limited, small changes in animal exercise duration can corresponded to untenable amounts of human exercise. To address this limitation, we introduce the Life-Span Relative Exercise Time (RET_{life span}) as a method of accurately defining short-term, medium-term and long-term exercise relative to the animal's life expectancy. Systematic organization of existent protocols and this new system of defining exercise duration will allow for a more solid framework from which researchers can extrapolate animal model data to clinical application.