title: A new method to determine the electrical transfer function of the human thorax.
abstract: Traditional analyses have assumed that cardiac electrical activity is reflected on the surface ECG without distortion as the signal passes through the body tissues. This study aims to explore the frequency dependence of thoracic attenuation of surface-recorded intracardiac electrical activity. Twenty patients (14 men, 55 +/- 15 yr of age) undergoing electrophysiological study were enrolled. Rectangular unipolar stimuli were applied from a catheter positioned in the right ventricular apical area and another in the posteroseptal area without contact with the myocardium. An orthogonal Frank-lead surface ECG and a unipolar intracardiac electrogram near the pacing site were recorded. Frequency domain characteristics of the signal-averaged pacing impulses were analyzed. Linear regression analysis showed significant frequency-dependent attenuation in the magnitude transfer functions (R(2) = 0.84-0.89, P < 0.0001) and good linear fit for the phase transfer characteristics (R(2) = 0.98-1.0, P < 0.0001). Age, physical dimension, and respiratory characteristics had significant effects on the magnitude and phase characteristics of the transfer functions. Application of models of the low- and high-slope transfer functions to signal-averaged ECGs from 33 subjects showed differences in the attenuation of P and T waves relative to the QRS.
authors.affiliation: Division of Cardiac Electrophysiology, Bluhm Cardiovascular Institute, Northwestern University Feinberg School of Medicine, 251 East Huron, Chicago, IL 60611, USA. j-goldberger@northwestern.edu
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Goldberger
authors.forename: Haris
authors.initials: H
authors.lastname: Subacius
authors.forename: Indranil
authors.initials: I
authors.lastname: Sen-Gupta
authors.forename: David
authors.initials: D
authors.lastname: Johnson
authors.forename: Alan H
authors.initials: AH
authors.lastname: Kadish
authors.forename: Jason
authors.initials: J
authors.lastname: Ng
mesh_terms: D000200:Action Potentials; D000328:Adult; D000367:Age Factors; D000368:Aged; D049628:Body Size; D017097:Electric Impedance; D004562:Electrocardiography / Q000379:methods*; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D005583:Fourier Analysis; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D015656:Respiratory Mechanics; D012815:Signal Processing, Computer-Assisted; D013909:Thorax / Q000503:physiopathology*; D013997:Time Factors