A new tool for the action potential repolarization dynamic analysis: Application to the discrimination of diabetic and control cells

In CinC2015 we have shown that the dynamics of the action potential (AP) repolarization could be tracked throughout the stimulation course. Despite some valuable outcomes, the populations of interest (control, Ctrl, and streptozotocin-induced, STZ, diabetic mice) could not be significantly distinguished in term of dynamics because of the global extracted feature. In this study, the computation of new features for each repolarization percentage allows an accurate and meaningful characterization of the two groups leading to a significant classification. APs in isolated left ventricular cardiomyocytes obtained from Ctrl and STZ mice were measured by patch-clamp. The progressive changes in AP repolarization for individual cells were tested on a set of 100 consecutive excitations at 2Hz pacing rate. The corresponding repolarizations are stacked in a matrix decomposed with a new approach. Observations are modeled as a sum of vectors multiplied by specific polynomial functions. This approach is similar to the Singular Value Decomposition (SVD), but the corresponding scalars are replaced by these functions. Model unknowns are estimated by using an alternated least square algorithm. Finally, the mean of the polynomial first derivative is computed for each repolarization percentage as a representative feature. A Wilcoxon signed rank test (p<;0.05) has been applied on the features from the two groups. We can observe a significant difference in the late repolarization phase (70%-95% repolarization), with a singular behavior in correspondence with the AP profile shoulder onset (80%).