Circulation, Vol 87, 199-207, Copyright © 1993 by American Heart Association
MA Fallert, MS Mirotznik, SW Downing, EB Savage, KR Foster, ME Josephson and DK Bogen
BACKGROUND. This study was designed to examine the bulk electrical
properties of myocardium and their variation with the evolution of
infarction after coronary occlusion. These properties may be useful in
distinguishing between normal, ischemic, and infarcted tissue on the basis
of electrophysiological parameters. METHODS AND RESULTS. The electrical
impedance of myocardial tissue was studied in a sheep model of infarction.
The animal model involved a one-stage ligation of the left anterior
descending and second diagonal arteries at a point 40% of the distance from
the apex to the base. By use of a four-electrode probe, an epicardial
mapping system was developed that allowed for cardiac cycle gated and
signal-averaged measurements. Subthreshold current (15 microA) was injected
through two of the electrodes at frequencies of 1, 5, and 15 kHz and the
induced potential measured with the other two electrodes. Epicardial maps
of the left ventricle were obtained during acute infarction and at 1-, 2-,
and 6-week intervals after occlusion. Results showed the average specific
impedance of the myocardium before infarction to be 158 +/- 26 omega-cm
independent of location on the epicardium. By 60 minutes after coronary
occlusion, the specific impedance had increased by 199% (p < 0.005, n =
9); it remained elevated for up to 4 hours. One week after infarction, the
specific impedance decreased to 59% of the control value (p < 0.025, n =
8). Six weeks after occlusion, the specific impedance remained low at 57%
of that of the noninfarcted tissue (p < 0.005, n = 9). The phase angle
of the complex impedance was also measured and revealed similar changes.
The hydroxyproline content of the tissue was assayed to assess infarct
healing. CONCLUSIONS. In this animal model, impedance is a bulk electrical
property of tissue that varies with the evolution of myocardial infarction.
Impedance mapping revealed significantly different values for normal,
ischemic, and infarcted tissue and may prove useful in better defining the
electrophysiological characteristics of such tissue.
ARTICLES
Myocardial electrical impedance mapping of ischemic sheep hearts and healing aneurysms
Department of Medicine, University of Pennsylvania, Philadelphia.
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