A simplified 3D model of whole heart electrical activity and 12-lead ECG generation

Abstract

We present a computationally efficient three-dimensional bidomain model of torso-embedded whole heart electrical activity, with spontaneous initiation of activation in the sinoatrial node, incorporating a specialized conduction system with heterogeneous action potential morphologies throughout the heart. The simplified geometry incorporates the whole heart as a volume source, with heart cavities, lungs, and torso as passive volume conductors. We placed four surface electrodes at the limbs of the torso: V R , V L , V F and V GND and six electrodes on the chest to simulate the Einthoven, Goldberger-augmented and precordial leads of a standard 12-lead system. By placing additional seven electrodes at the appropriate torso positions, we were also able to calculate the vectorcardiogram of the Frank lead system. Themodel was able to simulate realistic electrocardiogram (ECG) morphologies for the 12 standard leads, orthogonal X, Y, and Z leads, as well as the vectorcardiogram under normal and pathological heart states. Thus, simplified and easy replicable 3D cardiac bidomain model offers a compromise between computational load and model complexity and can be used as an investigative tool to adjust cell, tissue, and whole heart properties, such as setting ischemic lesions or regions of myocardial infarction, to readily investigate their effects on whole ECG morphology.

Figure 1

3D geometry of the model with subdomains labelled as follows: 1 = torso, 2 = lungs, 3 = atria and ventricles, and 4 = cardiac blood chambers, observed in the frontal plane (left) and the transverse plane (right).

Figure 2

Frontal views of model showing placement of all ECG leads. (a) ECG electrodes are placed at the four corners of the torso, yielding surface potentials (V) of the right arm (V _R), the left arm (V _L), the left leg (V _F), and the right leg (V _GND). Additional six precordial leads, V ₁, V ₂, V ₃, V ₄, V ₅,  and  V ₆, were placed at the chest near the heart. (b) The seven electrodes (A, C, E, F, H, I anteriorly, and M posteriorly) are placed to form a Frank lead system for determining orthogonal X, Y, and Z components for the vectorcardiogram.

Figure 3

Whole heart layout with semitransparent views in the right panels and sectioned views illustrating the various subdomains of the heart in panels on the right. Subdomain numbering is as follows: 1 = sinoatrial node, 2 = atria, 3 = atrioventricular node, 4 = His bundle, 5 = bundle branches, 6 = Purkinje fibers, and 7 = ventricular myocardium.

Figure 4

V _m transmembrane potential (TMP) at the heart surface (a) and in a frontal plane cross section midway through the heart (b), when the depolarization wave front first excites the left and right ventricles and when atrial repolarization has just begun.

Figure 5

Simulated lead II ECG signal and corresponding whole heart activation sequences at various time points on the ECG signal. The numeric labels on the ECG mark the moments in which the matching activation sequences below are illustrated. The color bar at Figure 4 also applies for the current figure.

Figure 6

Simulation of normal electrical activity. (a) Frontal plane cross section midway through the heart with the probe locations (black dots) positioned throughout the myocardium according to sinoatrial node (SAN), right atria (RA), left atria (LA), atrioventricular node (AVN), His bundle (HIS), bundle branches (BNL), Purkinje fibers (PKJ), right ventricle (RV), and left ventricle (LV). (b) Simulated lead II ECG waveform and the transmembrane action potentials at the probe positions.

Figure 7

Simulated transmembrane potential V _m at the epicardial surface in normal heart (a), heart with anterior MI (b), and heart with inferior MI (c).

Figure 8

Simulated Lead II ECG (a) and precordial lead V ₁ (b) for the three cases: normal heart (blue), anterior MI (red), and inferior MI (green).

Figure 9

Simulated 12 ECG leads for three cases: normal heart (blue), heart with anterior MI (red), and heart with inferior MI (green). V _I, V _II, and V _III refer to the three Einthoven leads; aV _R, aV _L, and aV _F are the augmented limb leads, whilst V ₁–V ₆ denote the six precordial leads.

Figure 10

Simulated vectorcardiogram (VCG) (b) and X, Y, and Z orthogonal ECG leads (a) for three cases: normal heart (blue), heart with anterior MI (red), and heart with inferior MI (green).