Continuous ST-segment monitoring during coronary angioplasty using orthogonal ECG leads

In order to characterize ST-segment shifts during transient coronary artery occlusion, 24 patients with single-vessel disease were continuously monitored during percutaneous transluminal coronary angioplasty by use of a computerized orthogonal lead system. Changes of ST-segment (J + 60 ms) in leads X, Y, and Z and of the ST vector magnitude were analyzed by using 20 microV as a threshold for significant ST-segment shift. The sensitivity and magnitude of this shift were compared among the left anterior descending, right coronary, and circumflex artery groups (11, 8, and 5 patients, respectively) during balloon inflation. Significant ST-segment shifts were seen in 22 patients (92%) in ST-VM, Y, and Z leads and all patients in lead X (100%). There was no significant difference in sensitivity of either the ST vector magnitude or the most sensitive lead for occlusion detection among the three groups. There was a significantly greater magnitude of ST shift during left anterior descending artery occlusion than during right coronary artery and circumflex artery occlusions in ST-VM. Analysis of the direction of ST shifts in the X, Y, and Z leads showed a characteristic pattern, which could distinguish among the three coronary groups in 21 patients (88%). The presence of collaterals was significantly associated with ST-segment depression in leads oriented toward ischemia (3 of 6 patients) as compared with ST-segment elevation in the absence of collaterals (all of 15 patients), P > .01. It is concluded that ST-segment shift in the orthogonal leads is a reliable marker for myocardial ischemia. It is equally sensitive to occlusion of each of the three major coronary arteries and can thus identify the occluded coronary. An ST-segment depression instead of an elevation was related to the presence of collaterals, which may reflect a lesser degree of ischemia.