Fig. 2.

Linear relationship between action potential (AP) duration (APD) at 20% and 50% repolarization (APD₂₀ and APD₅₀) properties at five pacing frequencies ex vivo. Experimental data are shown as crosses, dashed-dotted lines are the least-squares fits to the data (corresponding R² value given at the top of each plot), and solid black lines represent constraints corresponding to aAPD₂₀ + b_upper ≥ APD₅₀ ≥ aAPD₂₀ + b_lower imposed on APD₂₀ and APD₅₀ properties generated by in silico models. The constant a was obtained from the least-squares fit, whereas b_lower and b_upper were determined from the values of the outermost experimental data points.