Developing a pediatric organotypic slice model to study cardiac development in humans

The human heart continues to develop after birth and into adolescence – not reaching maturity until nearly the first decade of life. As such, there are considerable knowledge gaps in our understanding of cardiac physiology and pathology throughout the postnatal to juvenile period. These knowledge gaps can have unintended consequences, particularly when pharmacological therapies are designed with the adult in mind – targeting ion channels or signaling pathways that may not be fully developed in the immature heart. This study aimed to develop a technique to preserve human cardiac tissue for physiological measurements at baseline and in response to cardiovascular medications. We hypothesized that preparing thin tissue slices would preserve tissue ultrastructure and support cell viability, thus allowing for highly translatable electrophysiology studies. As a child is placed on cardiopulmonary bypass, a small piece of the right atrium may be removed to allow for cannulation; additionally, ventricular tissue may be discarded during repair. After surgical removal, these discarded samples are immediately transferred to the research laboratory for experimentation. A vibrating microtome was used to cut tissue slices to 380 microns and Fluo 4-AM was used to assess optical calcium transients. Cell viability was maintained with approximately 85% of cells alive immediately post-slicing and 78% viable 3-5 hours later. Additionally, slices can be maintained for up to 40 days allowing for long term drug screening. Organotypic slices were responsive to external pacing and the calcium transient duration at 80% repolarization (CaD80) was frequency dependent - shortening from an average of 996 ms at 0.2 Hz to 581 ms at 1 Hz and 486 ms at 2 Hz (room temperature) in tissue slices prepared from pediatric patients <1 year old. Each cardiac tissue sample yielded multiple slices, allowing for the comparison of multiple medications within a drug class to be assessed per patient. Tissue slices were responsive to 1-10 micromolar (μM) of catecholamines (isoproterenol, epinephrine, norepinephrine, and dopamine) and phosphodiesterase inhibitors (milrinone). For example, neonates treated with isoproterenol experienced a 25-32% shortening of CaD80 at 1-10 μM, respectively (baseline: 573 ms; 1 μM: 430 ms; 10 μM: 390 ms). Calcium imaging is reliable and reproducible with signals acquired in patients ranging from neonates to young adults having both simple and complex congenital heart defects thus allowing for the comparison of electrophysiologic responses across the pediatric age spectrum and multiple cardiac conditions. Using human cardiac tissue slices as a model for drug testing in adults has been accepted as a reliable technique for years. Our results show that cardiac tissue slices, from both the right atria and ventricle, can model pediatric cardiac physiology and may be a valuable asset in testing the safety of off label medications commonly used in pediatric patients. F31HL165818 to DG; R01HD108839 to NGP This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.