AimsDiseased atria are characterized by functional and structural heterogeneities, adding to abnormal impulse generation and propagation. These heterogeneities are thought to lie at the origin of... Show moreAimsDiseased atria are characterized by functional and structural heterogeneities, adding to abnormal impulse generation and propagation. These heterogeneities are thought to lie at the origin of fractionated electrograms recorded during sinus rhythm (SR) in atrial fibrillation (AF) patients and are assumed to be involved in the onset and perpetuation (e.g. by re-entry) of this disorder. The underlying mechanisms, however, remain incompletely understood. Here, we tested whether regions of dense fibrosis could create an electrically isolated conduction pathway (EICP) in which re-entry could be established via ectopy and local block to become ‘trapped’. We also investigated whether this could generate local fractionated electrograms and whether the re-entrant wave could ‘escape’ and cause a global tachyarrhythmia due to dynamic changes at a connecting isthmus.Methods and resultsTo precisely control and explore the geometrical properties of EICPs, we used light-gated depolarizing ion channels and patterned illumination for creating specific non-conducting regions in silico and in vitro. Insight from these studies was used for complementary investigations in virtual human atria with localized fibrosis. We demonstrated that a re-entrant tachyarrhythmia can exist locally within an EICP with SR prevailing in the surrounding tissue and identified conditions under which re-entry could escape from the EICP, thereby converting a local latent arrhythmic source into an active driver with global impact on the heart. In a realistic three-dimensional model of human atria, unipolar epicardial pseudo-electrograms showed fractionation at the site of ‘trapped re-entry’ in coexistence with regular SR electrograms elsewhere in the atria. Upon escape of the re-entrant wave, acute arrhythmia onset was observed.ConclusionsTrapped re-entry as a latent source of arrhythmogenesis can explain the sudden onset of focal arrhythmias, which are able to transgress into AF. Our study might help to improve the effectiveness of ablation of aberrant cardiac electrical signals in clinical practice. Show less
Background: Optogenetics could offer a solution to the current lack of an ambulatory method for the rapid automated cardioversion of atrial fibrillation (AF), but key translational aspects remain... Show moreBackground: Optogenetics could offer a solution to the current lack of an ambulatory method for the rapid automated cardioversion of atrial fibrillation (AF), but key translational aspects remain to be studied. Objective: To investigate whether optogenetic cardioversion of AF is effective in the aged heart and whether sufficient light penetrates the human atrial wall. Methods: Atria of adult and aged rats were optogenetically modified to express light-gated ion channels (i.e., red-activatable channelrhodopsin), followed by AF induction and atrial illumination to determine the effectivity of optogenetic cardioversion. The irradiance level was determined by light transmittance measurements on human atrial tissue. Results: AF could be effectively terminated in the remodeled atria of aged rats (97%, n = 6). Subsequently, ex vivo experiments using human atrial auricles demonstrated that 565-nm light pulses at an intensity of 25 mW/mm(2) achieved the complete penetration of the atrial wall. Applying such irradiation onto the chest of adult rats resulted in transthoracic atrial illumination as evidenced by the optogenetic cardioversion of AF (90%, n = 4). Conclusion: Transthoracic optogenetic cardioversion of AF is effective in the aged rat heart using irradiation levels compatible with human atrial transmural light penetration. Show less
Nyns, E.C.A.; Jin, T.Y.; Fontes, M.S.; Heuvel, T. van den; Portero, V.; Ramsey, C.; ... ; Pijnappels, D.A. 2021
Aims: Ventricular tachyarrhythmias (VTs) are common in the pathologically remodelled heart. These arrhythmias can be lethal, necessitating acute treatment like electrical cardioversion to restore... Show moreAims: Ventricular tachyarrhythmias (VTs) are common in the pathologically remodelled heart. These arrhythmias can be lethal, necessitating acute treatment like electrical cardioversion to restore normal rhythm. Recently, it has been proposed that cardioversion may also be realized via optically controlled generation of bioelectricity by the arrhythmic heart itself through optogenetics and therefore without the need of traumatizing high-voltage shocks. However, crucial mechanistic and translational aspects of this strategy have remained largely unaddressed. Therefore, we investigated optogenetic termination of VTs (i) in the pathologically remodelled heart using an (ii) implantable multi-LED device for (iii) in vivo closed-chest, local illumination. Methods and results: In order to mimic a clinically relevant sequence of events, transverse aortic constriction (TAC) was applied to adult male Wistar rats before optogenetic modification. This modification took place 3 weeks later by intravenous delivery of adeno-associated virus vectors encoding red-activatable channelrhodopsin or Citrine for control experiments. At 8-10 weeks after TAC, VTs were induced ex vivo and in vivo, followed by programmed local illumination of the ventricular apex by a custom-made implanted multi-LED device. This resulted in effective and repetitive VT termination in the remodelled adult rat heart after optogenetic modification, leading to sustained restoration of sinus rhythm in the intact animal. Mechanistically, studies on the single cell and tissue level revealed collectively that, despite the cardiac remodelling, there were no significant differences in bioelectricity generation and subsequent transmembrane voltage responses between diseased and control animals, thereby providing insight into the observed robustness of optogenetic VT termination. Conclusion: Our results show that implant-based optical cardioversion of VTs is feasible in the pathologically remodelled heart in vivo after local optogenetic targeting because of preserved optical control over bioelectricity generation. These findings add novel mechanistic and translational insight into optical ventricular cardioversion. Show less
In this thesis molecular and environmental cues in cardiac differentiation of mesenchymal stem cells were investigated. The main conclusions were that the cardiac differentiation potential of human... Show moreIn this thesis molecular and environmental cues in cardiac differentiation of mesenchymal stem cells were investigated. The main conclusions were that the cardiac differentiation potential of human mesenchymal stem cells negatively correlates with donor age. This in its own shows a negative relationship with connexin 43 levels in these cells. However, a causal relationship between connexin 43 expression levels and cardiomyogenic differentiation potential only exists for human mesenchymal stem cells from prenatal sources, i.e. while knockdown of connexin 43 expression in fetal human mesenchymal stem cells inhibits their ability to differentiate into cardiomyocytes, connexin 43 overexpression in adult human mesenchymal stem cells does not endow them with cardiomyogenic differentiation capacity. In addition, co-culture studies showed that the alignment and distribution of mesenchymal stem cells affect their electrical integration into host myocardium and are major determinants of their pro-arrhythmic risk. The mechanisms underlying the pro-arrhythmic effects of hMSCs are to some extent comparable to those of cardiac myofibroblasts, cells that are found in fibrotic myocardium Show less
Mesenchymal stem cells (MSCs) show unexplained differences in differentiation potential. In this study, differentiation of human (h) MSCs derived from embryonic, fetal and adult sources toward... Show moreMesenchymal stem cells (MSCs) show unexplained differences in differentiation potential. In this study, differentiation of human (h) MSCs derived from embryonic, fetal and adult sources toward cardiomyocytes, endothelial and smooth muscle cells was investigated. Labeled hMSCs derived from embryonic stem cells (hESC-MSCs), fetal umbilical cord, bone marrow, amniotic membrane and adult bone marrow and adipose tissue were co-cultured with neonatal rat cardiomyocytes (nrCMCs) or cardiac fibroblasts (nrCFBs) for 10 days, and also cultured under angiogenic conditions. Cardiomyogenesis was assessed by human-specific immunocytological analysis, whole-cell current-clamp recordings, human-specific qRT-PCR and optical mapping. After co-culture with nrCMCs, significantly more hESC-MSCs than fetal hMSCs stained positive for a-actinin, whereas adult hMSCs stained negative. Furthermore, functional cardiomyogenic differentiation, based on action potential recordings, was shown to occur, but not in adult hMSCs. Of all sources, hESC-MSCs expressed most cardiac-specific genes. hESC-MSCs and fetal hMSCs contained significantly higher basal levels of connexin43 than adult hMSCs and co-culture with nrCMCs increased expression. After co-culture with nrCFBs, hESC-MSCs and fetal hMSCs did not express a-actinin and connexin43 expression was decreased. Conduction velocity (CV) in co-cultures of nrCMCs and hESC-MSCs was significantly higher than in co-cultures with fetal or adult hMSCs. In angiogenesis bioassays, only hESC-MSCs and fetal hMSCs were able to form capillary-like structures, which stained for smooth muscle and endothelial cell markers. Human embryonic and fetal MSCs differentiate toward three different cardiac lineages, in contrast to adult MSCs. Cardiomyogenesis is determined by stimuli from the cellular microenvironment, where connexin43 may play an important role. Show less
Askar, S.F.A.; Ramkisoensing, A.A.; Schalij, M.J.; Bingen, B.O.; Swildens, J.; Laarse, A. van der; ... ; Pijnappels, D.A. 2011
Cardiovascular disease remains one of the most important causes of mortality. Over the past decades important advances have been made in prevention and treatment of acute complications after... Show moreCardiovascular disease remains one of the most important causes of mortality. Over the past decades important advances have been made in prevention and treatment of acute complications after myocardial infarction (MI). As a result, the number of patients that acutely die from MI has been reduced. Current treatments can not prevent the loss of cardiac contractility caused by cardiomyocyte death, and therefore patients that do survive MI are prone to develop progressive impaired cardiac function, which may lead to heart failure. Cell-based therapy has been proposed as a potential new therapy to prevent progression to end-stage heart failure by (re) generating contractile tissue in the damaged heart. During the last years many different cell sources have been studied extensively for their cardiomyogenic differentiation capacity in vitro and in vitro. These cells include several populations of cardiac-derived progenitor cells as well as mesenchymal stem cells derived from different sources. It has become clear that not only the origin, but also the "age" of a cell is an important determinant of its plasticity. Therefore, special attention is paid to the difference in developmental state of the cell sources and the consequences for their differentiation capacity and therapeutic applicability. Furthermore, we provide future perspectives for several aspects of cell-based therapy that could be optimized in order to enhance the regeneration of the heart. Show less
