Simultaneous Evaluation of Cardiac Wall Motion and Myocardial Ischemic Injury by Measurement of Electrical Impedance

The authors devised a new method to simultaneously evaluate cardiac wall motion and myocardial ischemic injury by measurement of myocardial electrical impedance. This method is based on the principle that electrical properties of the myocardium are affected by intra- or extracellular structure. Impedance was assessed by measuring voltage while a constant alternating current (0.4 mA, 50 kHz) was being applied to the myocardium by way of an electrode that had two parallel 6 mm long needles. In five dogs, an electrode was placed in the left ventricular wall, adjacent to a pair of ultrasonic crystals that were used to estimate regional wall thickness. To change regional contractility and to induce ischemic injury, the left anterior descending coronary artery was ligated. The impedance waveforms were observed to be synchronized with cardiac contraction, and changes in impedence correlated well with changes in wall thickness. Dyskinetic movements in the ischemic myocardium could also be detected through assessment of the impedance waveform. During the first 2 hr, the average value of impedance increased significantly, from 254 +/- 38 omega-cm to 329 +/- 13 omega-cm (P < 0.005), and then decreased, indicating a correlation with the progression and irreversibility of ischemic injury. This simple technique may eventually allow us to simultaneously assess cardiac wall motion and myocardial ischemia in humans.