Multiple components in the unipolar electrogram: a simulation study in a three-dimensional model of ventricular...

Area of Science:

• Computational Biology
• Electrophysiology
• Biophysics

Background:

• Traditional models of cardiac electrical activity, such as the uniform and oblique dipole layers, struggle to explain experimental electrogram (EG) data.
• Inconsistencies between existing models and experimental findings necessitate a reevaluation of unipolar EG interpretation.

Purpose of the Study:

• To develop and utilize a numerical model simulating excitation spread in myocardial tissue.
• To identify factors influencing the shape, amplitude, and polarity of unipolar electrograms (EGs).

Main Methods:

• A parallelepipedal bidomain model of myocardial tissue with anisotropic properties and fiber rotation was implemented.
• Eikonal equations calculated excitation spread, and fixed action potential shapes determined potential distributions.
• Unipolar electrograms (EGs) were computed from time-varying potential distributions at multiple sites.

Main Results:

• Unipolar QRS waveforms are composed of a "field" component (wavefront proximity) and a newly identified "reference" component.
• The "reference" component arises from the drift of the reference potential during excitation spread.
• This reference potential shifts from positive to negative extremes during excitation propagation.

Conclusions:

• The reference potential drift reconciles discrepancies between cardiac models and observed EG shapes.
• This drift impacts the assessment of excitation/recovery times and QRS/ST-T areas.
• Correcting for reference potential drift restores consistency between potential distributions and electrographic waveforms.