EPICARDIAL MAPPING AND ELECTROCARDIOGRAPHIC MODELS OF MYOCARDIAL ISCHEMIC-INJURY

The amplitude and distribution of epicardial ST-segment elevation (ST↑) were examined for an 8-hour period after coronary occlusion in eight baboons and five pigs. ST↑ was determined from unipolar epicardial electrograms obtained from a high-resolution matrix of fixed electrodes overlying a transmural region of ischemia. A relatively uniform degree of ST↑ was observed overlying the ischemic region for 20 minutes after coronary occlusion. A gradient in ST↑ from the periphery to the center of the ischemic region was documented after 20 minutes of ischemia. In 10 other pigs, change in the degree of ST↑ was examined contingent on either an increase (five pigs) or decrease (five pigs) in the size of the ischemic region after 1 hour of preexisting ischemia. An abrupt increase in the number of electrodes that showed ST↑ (NST) from 7.8 ±1.24 (SEM) to 14.8 ± 1.35 (90%) was associated with an increase in mean ST↑ of 58% from 4.28 ± 0.61 mV to 6.78 ± 0.84 (p<0.05). An abrupt decrease in NST from 25.2 ±2.63 to 14.6 ± 22.2 (42%) was associated with a decrease in mean ST↑ of 24%, from 8.2 ± 0.36 mV to 6.3 ± 0.30 mV (p<0.01). The results during early ischemia (less than 20 minutes of ischemia) are accurately represented by a model of ischemia in which injury current arises only at the ischemic boundary. The results during later ischemia (after 20 minutes of ischemia) may be represented by a model in which ST↑ is considered dependent on injury currents generated throughout the ischemic region.