Abstract 210: Assessment of Cardiac Cell Culture Electrical Excitability Using Strength Duration Relationships

Abstract

Understanding the factors that influence the electrical excitability is important for successful engineering and therapeutic translation of cardiac tissue. Electric field excitation is widely utilized in vitro and in vivo to assess the response of cardiomyocytes to electrical excitation. The excitability of cardiac tissue is influenced by a variety of factors, including anatomic location in the heart, disease status, and age. We dissect properties that alter the electrical excitability of ventricular myocardial tissue constructs in vitro in 2D and 3D models of neonatal rat ventricular myocytes, using a custom-made integrated live-cell imaging and pacing setup. We find that for both 2D and 3D constructs, the electrical signal strength correlates negatively with the threshold stimulation duration required for pacing and driving the engineered tissue, and the resulting strength-duration curve is well approximated by the Lapicque-Hill model of electrically excitable membranes. By comparing strength-duration relationships, we find that pacing 2D constructs at 2 Hz requires 1.7 to 1.9 times the stimulus strength compared to pacing at 1 Hz (n=3, p<0.05). Similarly, we find that pacing 3D constructs at 3 Hz requires 1.2 to 1.5 times the stimulus duration compared to pacing at 1 Hz (n=3, p<0.05). By comparing strength-duration relationships of 3D spheroids of diameters ranging from 100 to 210 um (n=7), we find that the signal strength required for capture at 10 ms duration correlates negatively with the spheroid diameter (r =-0.87, p=0.02). When cell culture anisotropy is induced by seeding the cells on abraded plastic substrate, we find that a 1.3 to 1.9 times higher threshold duration of stimulus is required to pace and drive cultures aligned perpendicular to the direction of the electric field compared to those aligned parallel to the direction of the electric field (n=3, p<0.05). Finally, when fibroblasts are added in equal density to the NRVMs, we find a significant increase in threshold duration at lower stimulation strength (n≥2, p<0.05). Therefore, we conclude that 2D and 3D primary NRVM cultures are better electrically entrained when driven at slower frequencies, are large in size and aligned with the electric field, and have low fibroblast content.