Characterization of ventricular depolarization and repolarization changes in a porcine model of myocardial infarction

In this study, several electrocardiogram (ECG)-derived indices corresponding to both ventricular depolarization and repolarization were evaluated during acute myocardial ischemia in an experimental model of myocardial infarction produced by 40 min coronary balloon inflation in 13 pigs. Significant changes were rapidly observed from minute 4 after the start of coronary occlusion, achieving their maximum values between 11 and 22 min for depolarization and between 9 and 12 min for repolarization indices, respectively. Subsequently, these maximum changes started to decrease during the latter part of the occlusion. Depolarization changes associated with the second half of the QRS complex showed a significant but inverse correlation with the myocardium at risk (MaR) estimated by scintigraphic images. The correlation between MaR and changes of the downward slope of the QRS complex, I_DS, evaluated at the two more relevant peaks observed during the occlusion, was r = −0.75, p < 0.01 and r = −0.79, p < 0.01 for the positive and negative deflections observed in I_DS temporal evolution, respectively. Repolarization changes, analyzed by evaluation of ST segment elevation at the main observed positive peak, also showed negative, however non-significant correlation with MaR: r = −0.34, p = 0.28. Our results suggest that changes evaluated in the latter part of the depolarization, such as those described by I_DS, which are influenced by R-wave amplitude, QRS width and ST level variations simultaneously, correlate better with the amount of ischemia than other indices evaluated in the earlier part of depolarization or during the ST segment. (paper)