Myocardial electrical activity does not affect myocardial electrical impedance measurements.
OBJECTIVE
Myocardial electrical impedance (MEI) has shown to be an effective indicator of myocardial ischemia. We have previously developed a novel monitor for measuring MEI in near-real time. The object of this study was to test whether drug-induced changes in the frequency of the periodic myocardial electrical activity, as measured by the heart rate (HR), affect MEI measurements made with our monitor.


METHODS
Thirty dogs were randomly assigned to one of three study groups (placebo, isoproterenol or esmolol) and then anesthetized with sodium thiamylal, intubated, ventilated, given isoflurane, and had venous, arterial, and pulmonary artery catheters placed. Median sternotomy was performed to facilitate myocardial exposure and to allow the left anterior descending (LAD) coronary artery to be isolated. Following baseline measurements, saline (control), isoproterenol or esmolol was administered and the LAD coronary artery was occluded in a timed sequence in order to study the effects of heart rate changes and demonstrate induced myocardial ischemia on MEI.


RESULTS
Isoproterenol raised the HR and esmolol lowered the HR without affecting our MEI measurements. Myocardial electrical impedance increased during LAD coronary artery occlusion in all groups, as previously shown.


CONCLUSIONS
These results demonstrate that our MEI monitor is unaffected by the frequency of the periodic myocardial electrical activity that generates the HR.
Dzwonczyk
Roger
R
Department of Anesthesiology, The Ohio State University, Doan Hall, Columbus, OH 43210-1228, USA. dzwonczyk.1@osu.edu
del Rio
Carlos
C
McSweeney
Thomas D
TD
Zhang
Xiaoli
X
Howie
Michael B
MB
D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects; D003331:Coronary Vessels / Q000473:pathology; D004285:Dogs; D017097:Electric Impedance; D004563:Electrochemistry / Q000379:methods; D004594:Electrophysiology / Q000379:methods; D006321:Heart; D006339:Heart Rate / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D017202:Myocardial Ischemia / Q000175:diagnosis / Q000188:drug therapy / Q000503:physiopathology*; D009206:Myocardium / Q000378:metabolism; D010919:Placebos; D011412:Propanolamines / Q000494:pharmacology; D013997:Time Factors
D010919:Placebos; D011412:Propanolamines; D007545:Isoproterenol; C036604:esmolol