ST-segment depression in inferior ECG leads during percutaneous transluminal coronary angioplasty for left anterior descending artery.

The mechanism of inferior ST depression during percutaneous transluminal coronary angioplasty (PTCA) for the left anterior descending artery (LAD) was studied in 108 patients with isolated LAD lesion. In 49 patients (Group I) ST depression in inferior leads was observed, and 59 patients (Group II) showed no inferior ST depression. In the lateral lead (I or a VL), the incidence (43 cases; 88% vs. 5 cases; 9%) and degree (1.5 +/- 0.8 mm vs. 0.2 +/- 0.4) of ST elevation were significantly greater in Group I than in Group II. There was a significant inverse correlation (r = -0.57, p less than 0.01) between ST depression in the inferior lead and ST elevation in the lateral lead, but no correlation was found between anterior leads (V2-4) and the inferior leads. Elevation of diastolic pressure of the pulmonary artery (8.7 +/- 4.8 vs. 5.7 +/- 2.8 mmHg) and lowering of systolic pressure of the femoral artery (-25.7 +/- 24.3 vs. -11.8 +/- 8.3 mmHg) were significantly greater in Group I. These findings suggest that ST depression in the inferior leads during LAD angioplasty was due to a purely electrical phenomenon and not to the concomitant ischemia of the inferior wall. However, this change was more frequently seen in patients with larger myocardial ischemia and, presumably, was more often related to ST elevation in the lateral lead, which is reciprocal in position.