Abstract 17006: Reversing Membrane Clock Remodeling (MCR) Associated With Heart Failure With Preserved Ejection Fraction (HFpEF) in the Sinoatrial Node (SAN) Eliminates Chronotropic Incompetence (CI)

Introduction: While CI, or the inability of heart rate (HR) to adequately respond to exercise, is a strong indicator of mortality in HFpEF, treatment options remain limited as its mechanisms remain underexplored. Ionic remodeling of the SAN, both of the membrane (MC) and calcium clocks (CC), is associated with HFpEF and CI. Aim: Using an in silico approach, we investigated whether SAN ionic remodeling can contribute to 3 different CI presentations (Fig A) and explored the effectiveness of targeting the remodeling of the MC or CC (MCR and CCR, resp.) in eliminating CI. Methods: A human SAN model (control) was used, in which ionic remodeling was integrated using experimental data from HFpEF rat model with CI (Fig B top). A family of HFpEF SAN models (n = 147) was generated because the uniqueness of Ca 2+ handling parameters constrained to experimentally-based Ca 2+ transients could not be guaranteed (Fig B middle). To assess the level of CI, max beat rate (BR), BR response (τ on ), and BR recovery (τ off ) were quantified for each model in response to a transient 40s pulse of 1 μM isoproterenol (ISO) (Fig B bottom). Lastly, the effect of reversing either CCR or MCR on CI was determined. Results: Without ISO, BR of HFpEF SAN models was similar to that of control; when ISO was applied (Fig C), HFpEF models exhibited all aspects of CI: submaximal BR (Fig D), and elevated τ on and τ off (Fig E). In CCR reversed models, BR without ISO was similar to that of control; with ISO, they exhibited submaximal BR (Fig F). In MCR reversed models, BR without ISO was slightly lower compared to control; with ISO, while they exhibited submaximal BR, the increase in BR with ISO was similar to that of control (Fig F). τ on and τ off were elevated in CCR reversed models, but they were not in MCR reversed models (Fig G). In summary, CCR reversed models exhibited all aspects of CI, but MCR reversed models did not. Conclusion: Ionic remodeling of the SAN contributes to CI in HFpEF, and targeting MCR could be a promising strategy for eliminating CI.