A new method to determine the electrical transfer function of the human thorax

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Signal Processing

Background:

• Traditional electrocardiogram (ECG) analysis assumes cardiac electrical signals transmit through the body without distortion.
• This assumption may not hold true, potentially affecting the accuracy of surface ECG interpretations.

Purpose of the Study:

• To investigate the frequency-dependent attenuation of intracardiac electrical activity as it propagates to the body surface.
• To quantify the impact of thoracic tissues on the fidelity of cardiac electrical signals recorded via ECG.

Main Methods:

• Recorded intracardiac electrograms and orthogonal Frank-lead surface ECGs from 20 patients undergoing electrophysiological studies.
• Applied unipolar stimuli from right ventricular catheter positions.
• Analyzed frequency domain characteristics of signal-averaged pacing impulses using linear regression.

Main Results:

• Demonstrated significant frequency-dependent attenuation in the magnitude transfer functions (R(2) = 0.84-0.89, P < 0.0001).
• Showed a good linear fit for phase transfer characteristics (R(2) = 0.98-1.0, P < 0.0001).
• Identified age, physical dimensions, and respiratory characteristics as factors influencing signal transfer.

Conclusions:

• Thoracic attenuation significantly impacts surface-recorded cardiac electrical activity in a frequency-dependent manner.
• Models of transfer functions revealed differential attenuation of P and T waves compared to the QRS complex.
• Findings necessitate re-evaluation of ECG signal interpretation, considering tissue-induced distortions.