Changes in R wave amplitude: ECG differentiation between episodes of reocclusion and reperfusion associated with ST-segment elevation.

This study assesses the electrocardiographic (ECG) differences between episodes of increased ST-segment amplitude induced by coronary artery occlusion and by reperfusion in the open-chest rabbit model. Nine anesthetized open-chest male New Zealand White rabbits were subjected to four episodes of 5 minutes of coronary artery occlusion followed by 5 minutes of reperfusion. The ST-segment and R wave amplitudes were measured from an ECG lead attached to the pericardium overlying the ischemic myocardium. In 10 out of 35 (29%) of the episodes, reperfusion resulted in a transient increase in ST-segment amplitude. While episodes of coronary artery occlusion were associated with increase in R wave amplitude (69% and 97% of the episodes after 1 and 5 minutes, respectively), all reperfusion episodes were associated with prompt decrease in R wave amplitude. There was no difference between the repeated episodes in the occurrence of ST-segment elevation during reperfusion. However, ST-segment elevation during reperfusion could be distinguished from the ischemic episodes by the prompt decline in the R wave amplitude in the former compared with no change or increase in the latter.