OPTOCARD · Panoramic optical manipulation of cardiac electrical dynamics: a novel tool to study complex arrhythmias

Panoramic optical manipulation of cardiac electrical dynamics: a novel tool to study complex arrhythmias

Cardiovascular diseases are the most common cause of death worldwide, and a substantial number of these deaths are caused by cardiac arrhythmias resulting in sudden cardiac death. Cardiac arrhythmias are caused by disruptions in cardiac electrical activity, leading to a reduction to complete loss of the heart’s ability to maintain blood flow throughout the body. One of the mechanisms underlying these arrhythmias are driven by heterogeneities in repolarisation time (RT), which is the time in which cardiac muscle cells (cardiomyocytes) recover from electrical activation. These RT heterogeneities are caused by action potential (AP) prolongation or abbreviation in certain areas of the heart, and can be caused by inherited disease (i.e. genetic disorders causing ion channel dysfunction), but also occur secondary to acquired heart disease such as myocardial infarction. Current experimental methods aimed to explore the mechanisms causing arrhythmias rely on the infusion of drugs modulating AP duration (APD) in single coronary arteries to generate ventricular RT heterogeneities, limiting versatility of the spatial characteristics of the area with altered APD, as well as restricting studies to larger animal models. Therefore, the conditions facilitating sustained arrhythmia upon the presence of RT heterogeneities remain to be elucidated. In addition, while optical platforms offer the possibility to study cardiac electrical dynamics in a highly detailed manner, current state-of the-art optical platforms lack the possibilities required for the research objectives of this project. To accurately assess the arrhythmogenic effects of RT heterogeneities, it is vital to be able control optical stimulation across the entire ventricular surface. In the OptoCARD project, we aimed to develop a novel, state-of-the-art panoramic optical manipulation-and-detection platform to study and manipulate cardiac electrophysiological dynamics in mouse hearts. By using multiple cameras and projectors, and a centralised acquisition system, this platform enables us to perform organ-wide detection of electrical activity. To measure cellular transmembrane potential and thereby map action potentials, we implemented a red-shifted voltage-sensitive dye (VSD) which is excited by red light and emits light in the far-red spectrum. Manipulation of cardiac function is performed via the use of the light-activated ion channel Channelrhodopsin-2 (ChR2), which is activated by blue light. Hence, by using a mouse model with cardiac-specific expression of ChR2 and using the red-shifted VSD, we can perform simultaneous optical mapping and optogenetic stimulation with minimal optical crosstalk. The scientific goal of this project is to develop a new model to study mechanisms underlying generation and maintenance of lethal ventricular arrhythmias caused by heterogeneities in RT. Previous work by the supervisor’s group demonstrated that sub-threshold optogenetic stimulation, with an intensity insufficient to evoke an AP, induces a depolarization in single cells, translating to conduction slowing and delayed RT in the stimulated area of whole hearts. As such, this approach could allow for specific and fully reversible manipulation of RT and can therefore be used to gain insight in mechanisms driving cardiac arrhythmias in the setting of RT heterogeneities. In addition, patterned supra-threshold allows for the creation of non-conducting areas within the heart and thereby inducing conduction block. Together, these approaches enable advanced investigations of mechanisms driving arrhythmias by mimicking various pathological conditions. Combining this approach with a panoramic aspect allowing to measure and manipulate the entire heart, opens a new avenue of possibilities by gaining control over the entire myocardial surface and simultaneously measuring it. Apart from the panoramic optical manipulation-and-detection platform, we identified a pharmacological approach to enhance functional gradients induced by sub-threshold optogenetic stimulation. After an extensive literature study, patch-clamp studies were performed on isolated mouse cardiomyocytes to assess the impact of the selected drug, Flecainide. Here, we tested whether the drug Flecainide can be used to enhance heterogeneities in excitability to depolarised resting membrane potential. In addition, we applied the insights gained from these single cell experiments to the entire heart, where we performed sub-threshold optogenetic stimulation in combination with this pharmacological approach to enhance arrhythmia susceptibility. Together, this project contributes to the development of novel approaches to study arrhythmia mechanisms in mouse hearts. Scientific objectives: The scientific objectives and their status at the end of the project are as follows: Objective 1: Develop a panoramic optical platform for measuring and manipulating cardiac activity and employ the system to characterise the spatial properties of repolarisation manipulation. Objective 2: Establish RMP-dependent drugs and exploit this dependence to enhance RT gradients. Objective 3: Employ the newly developed panoramic optical platform and apply the established RMP- dependent drugs to understand the mechanisms underlying arrhythmia induction and rotor maintenance. Training objectives: Objective 1: Extend technical skills and knowledge in the field of cardiac functional imaging. Objective 2: Gain programming skills to become a more all-round researcher. Objective 3: Improve communication skills with general public.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз