Simulation of Subendocardial Ischemia: From the Action Potential to 12-lead ECG. Simulation of subendocardial ischemia from increased myocardial demand with ECGSIM. A. Heart – left upper: The left (top) and right (bottom) ventricles are shown so that the endocardium can be viewed. The entire endocardium of the left ventricle has been highlighted so that it appears as a lighter yellow color. B. TMP – left lower: The action potential (also known as transmembrane potential [TMP]) from a cell at the center of the ischemic region is shown. The baseline normal action potential is shown in white and the ischemic action potential is shown in red. The ischemic action potential has a shortened action potential depolarization (early repolarization) and decreased action potential amplitude (depolarized baseline). Depolarization has not been delayed (as was done with transmural ischemia) because this does not normally occur with subendocardial ischemia. C. Leads – on right: The normal baseline 12-lead ECG is shown in white and the simulated ECG from global subendocardial ischemia is shown in red. Horizontal or down-sloping ST-segment depression with inverted T-waves occurs in a large number of leads except for aVR, where there is ST segment elevation and a positive T wave. The associated video further demonstrates the relation between the individual action potential changes and the ECG changes. ECGSIM can be downloaded for free from www.ecgsim.org.

Simulation of Transmural Myocardial Ischemia: From the Action Potential to 12-lead ECG. Simulation of transmural myocardial ischemia from insufficient blood supply with ECGSIM. A. Heart – upper left: The right and left ventricles (RV and LV) are shown with the left anterior descending (LAD) coronary artery (red) running down between the two ventricles. An area of ischemic myocardium has been highlighted that appears as a lighter yellow color and correlates to transmural ischemia that could occur from a mid-to-distal LAD occlusion. The spatial location of the 6 precordial electrodes are shown. B. TMP– lower left: The action potential (also known as transmembrane potential [TMP]) from a cell at the center of the ischemic region is shown. The baseline normal action potential is shown in white and the ischemic action potential is shown in red. The ischemic action potential has a shortened action potential depolarization (early repolarization), decreased action potential amplitude (depolarized baseline) and delayed initiation of the upstroke (delayed depolarization). C. Leads – on right: The normal baseline 12-lead ECG is shown in white and the simulated ECG from transmural ischemia is shown in red. The most significant change arrears in lead V3, which has its positive pole most directly above the ischemic region, as seen in the upper left model of the heart. The ECG changes that occur in V3 are an increase in T wave amplitude, ST-segment elevation and changes to the terminal part of the QRS (disappearance of S wave and increase in R wave). These changes also occur in leads V4, I and aVL, which also have positive poles above the ischemic area. The associated video further demonstrates the relation between the individual action potential changes and the ECG changes. ECGSIM can be downloaded for free from www.ecgsim.org.

Understanding the Three-dimensional Electrocardiogram: From Vector Loops to the 12-lead ECG