Experimental Measures of the Minimum Time Derivative of the Extracellular Potentials as an Index of Electrical Activity During Metabolic and Hypoxic Stress

Abstract

The time of the minimum time derivative of the extracellular potentials (Φ ^∧) is a marker for the instant of activation when the depolarizing sodium current reaches its maximum rate of increase. This study examined the normalized averaged value of Φ ^∧, $\Phi{^\wedge_{na}}$, as an index of electrical activity under metabolic and hypoxic stresses. Electrical mapping was performed using a 64-electrode cage array on Langendorff perfused isolated mouse hearts at three different glucose and insulin levels during hypoxia. The lower levels of glucose and/or insulin resulted in the largest decrease of $\Phi^\wedge_{na}$ during hypoxia. A significant decrease in $\Phi^\wedge_{na}$ was a predictor of increased total activation time and propagation pattern change, and irreversible damage was predicted by a 60% decrease of $\Phi^\wedge_{na}$. These results supported $\Phi^\wedge_{na}$ as an potentially useful index of electrical activity.