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The Annals of Thoracic Surgery, Vol 44, 587-597, Copyright © 1987 by The Society of Thoracic Surgeons
MI Ellenby, KW Small, RM Wells, DJ Hoyt and JE Lowe
The metabolic and physiological alterations associated with changes in
myocardial tissue electrical resistivity during ischemia were characterized
to assess the feasibility of using such resistivity as an on-line indicator
of the onset of ischemic injury. Twelve anesthetized dogs underwent rapid
cardiac extirpation; 5 served as untreated controls, and 7 were pretreated
with metoprolol tartrate. Beta blockade was used to alter the time course
of ischemic injury as demonstrated previously in studies using this
experimental model. In vitro measurement of myocardial resistivity, the
detection of ischemic contracture, and serial measurements of tissue
adenosine triphosphate (ATP) and lactate were obtained from totally
ischemic left ventricles at 37 degrees C. Myocardial resistivity began to
increase significantly before onset of ischemic contracture in the
untreated control group (resistivity at 42.3 +/- 3.1 minutes, contracture
at 53.8 +/- 3.7 minutes; p less than 0.025) as well as the metoprolol group
(resistivity at 50.7 +/- 1.5 minutes, contracture at 70.0 +/- 3.5 minutes;
p less than 0.005). As expected, ischemic contracture was delayed in the
beta-blocked group compared with controls (p less than 0.01). Similarly,
the onset of myocardial resistivity increase was delayed in the
beta-blocked group (p less than 0.025). ATP and lactate levels at the onset
of myocardial resistivity increase were consistent with severe but
reversible injury. Resistivity changes during ischemia correlated linearly
with simultaneous ATP depletion and lactate accumulation (r = 0.88 to 0.98;
p less than 0.05). Furthermore, during global ischemia studied in 3
anesthetized dogs in vivo, the onset of myocardial resistivity increase
occurred after 20 minutes. Finally, 6 anesthetized dogs underwent 60
minutes of in vivo regional ischemia by coronary artery occlusion, followed
by 60 minutes of reperfusion. Myocardial resistivity in the ischemic region
increased immediately and steadily after coronary occlusion, followed by a
rapid decrease during subsequent reperfusion. These data show that
myocardial resistivity may be useful for identifying severe but still
reversible ischemic injury in on-line fashion during regional and global
myocardial ischemia.
ARTICLES
On-line detection of reversible myocardial ischemic injury by measurement of myocardial electrical impedance
Department of Surgery, Duke University Medical Center, Durham, NC 27710.
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