Instantaneous current-voltage relationships during the course of the human cardiac ventricular action potential: new computational insights into repolarization dynamics.

Aims. To adopt a novel three-dimensional representation of cardiac action potential (AP) in order to compactly visualize dynamical properties of human cellular ventricular repolarization. Methods and results. We have recently established a novel three-dimensional representation of cardiac AP, which is based on iterative measurement of instantaneous ion current – voltage profiles during the course of an AP. Such approach has been originally developed on real patch clamped ventricular cells, and subsequently improved in silico on several cardiac ventricular AP models of different mammals, and on models of different AP types of the human heart. We apply it here on two different models of human ventricular AP, and show that it compactly provides further insights into repolarization dynamics. The 3D representation of the AP includes equilibrium points during repolarization, and can be screened in terms of what we have shown to be a region, during late repolarization, when membrane conductance becomes negative and repolarization therefore auto-regenerative. We have called this time window Auto-Regenerative-Repolarization-Phase (ARRP). Conclusion. In addition to previous findings obtained through the same procedure, we show here that 3D current-voltage-time representations of human ventricular AP allow compact visualization of dynamical properties, which are relevant for the physiology and pathology of ventricular repolarization. In particular, we suggest that the volume under the current surface corresponding to the ARRP might be used as predictor of safety of repolarization, in single cells and during AP conduction in cell pairs.