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CARDIOVASCULAR ANESTHESIA

An Evaluation of a New Two-Electrode Myocardial Electrical Impedance Monitor for Detecting Myocardial Ischemia

The Ohio State University Medical Center, Department of Anesthesiology, Columbus OH

Address correspondence and reprint requests to Michael B. Howie, MD, The Ohio State University Medical Center, Department of Anesthesiology, 410 West 10th Avenue, Columbus, OH 43210-1228.

The objective of this study was to determine the efficacy of a two-electrode myocardial electrical impedance (MEI) monitor in reproducibly detecting induced myocardial ischemia by comparing MEI changes with hemodynamic changes, including sonomicrometric changes. With institutional approval, 80 dogs were anesthetized with sodium thiamylal, intubated, ventilated, and had venous, arterial, and pulmonary artery catheters placed. Medial sternotomy was performed to facilitate myocardial exposure and allow the left anterior descending coronary artery (LAD) to be isolated. Two pacing electrodes were attached to the myocardium to measure MEI with a monitor. Seventy dogs were randomly assigned to the 15, 30, 45, 60, or 120 min LAD occlusion group. Sonomicrometric transducers were attached to the myocardium of the ten remaining dogs and their LAD was occluded for 36 min. MEI increased immediately after LAD occlusion to a level significantly more (P <0.05) than baseline and returned to the baseline level upon reperfusion. Twenty dogs developed ventricular fibrillation with no attempts at resuscitation. MEI changes paralleled the sonomicrometric changes expected with ischemia. No significant cardiovascular hemodynamic changes were found with less than 45 min of LAD occlusion. Sixty and 120 min LAD occlusion resulted in significant decreases in cardiac output. The results of these experiments demonstrate that the two-electrode MEI monitor reproducibly changes in response to myocardial ischemia.

Implications: We used dogs to determine if we could measure myocardial ischemia using a device that measures impedance and demonstrated that a two-electrode myocardial electrical impedance monitor reliably reflected changes induced by myocardial ischemia.

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