A dynamic model of the cardiac ventricular action potential. II. Afterdepolarizations, triggered activity, and potentiation.

Abstract

The action potential model presented in our accompanying article in this journal is used to investigate phenomena that involve dynamic changes of [Ca2+]i, as described below. Delayed afterdepolarizations (DADs) are induced by spontaneous Ca2+ release from the sarcoplasmic reticulum (SR), which, in turn, activates both the Na(+)-Ca2+ exchanger (INaCa) and a nonspecific Ca(2+)-activated current (Ins(Ca)). The relative contributions of INaCa and of Ins(Ca) to the generation of DADs are different under different degrees of Ca2+ overload. Early afterdepolarizations (EADs) can be categorized into two types: (1) plateau EADs, resulting from a secondary activation of the L-type Ca2+ current during the plateau of an action potential, and (2) phase-3 EADs, resulting from activation of INaCa and Ins(Ca) by increased [Ca2+]i due to spontaneous Ca2+ release from the SR during the late repolarization phase. Spontaneous rhythmic activity and triggered activity are caused by spontaneous Ca2+ release from the SR under conditions of Ca2+ overload. Postextrasystolic potentiation reflects the time delay associated with translocation of Ca2+ from network SR to junctional SR. The cell is paced at high frequencies to investigate the long-term effects on the intracellular ionic concentrations.

The role of M cells and the long QT syndrome in cardiac arrhythmias: Simulation studies of reentrant excitations using a detailed electrophysiological model

“…Typical currents that are responsible for the generation of early after depolarizations are fairly small. 34 For example, in the case studied here, the late I N a current is on the order of 2-4 µAcm −2 while in long QT 1 and long QT 2, the respective reduction of I Ks and I Kr is on the order of 1 µAcm −2 . Furthermore, the L type calcium current involved in the generation of early after depolarizations is roughly of the same magnitude.…”

Turbulent electrical activity at sharp-edged inexcitable obstacles in a model for human cardiac tissue

“…Time t is measured in milliseconds, voltage V in millivolts, conductances (GX) in nanosiemens per picofarad, the intracellular and extracellular ionic concentrations (Xi, Xo) in millimoles per liter, and current densities (IX) in microamperes per unit area in square centimeters, as used in second-generation models (see, e.g., Refs. 7,35,36,67). For a detailed list of the parameters of this model and the equations that govern the spatiotemporal behaviors of the transmembrane potential and currents see, e.g., References 61 and 67.…”

Mechanoelectric Feedback as a Trigger Mechanism for Cardiac Electrical Remodeling: A Model Study

“…12 In this model, calcium handling is based on the ventricular model by Luo and Rudy. 44,45 The formulation of Ca 2+ release from the SR reflects the close coupling of L-type Ca 2+ channels and SR Ca 2+ release channels. In addition, the formulation is completely analytic and does not require the identification of some trigger event (see Courtemanche et al 12 for details).…”