CORRELATION BETWEEN EXERCISE-INDUCED ISCHEMIC ST-SEGMENT DEPRESSION AND MYOCARDIAL BLOOD-FLOW QUANTIFIED BY POSITRON-EMISSION-TOMOGRAPHY

Background Ischemic ST-segment depression (horizontal or downsloping) is the most common manifestation of exercise-induced myocardial ischem ia. The mechanisms responsible for these types of ST-segment depressio n are largely unknown. We investigated the relation of these 2 types o f exercise-induced ST-segment depression to changes in regional myocar dial blood flow (RMBF) by using exercise positron emission tomography (PET). Methods and Results The RMBF was measured with nitrogen-13 ammo nia PET both at rest and during low-level supine bicycle exercise in 2 7 patients with angiographically proven coronary artery disease and in 6 healthy volunteers. ST-segment depression was measured from the iso electric PR segment 80 ms after the J point. Exercise-induced horizont al ST-segment depression greater than or equal to 0.1 mV was observed in 9 patients and downsloping depression greater than or equal to 0.1 mV was observed in 18 patients. Multivessel disease was more frequent and areas of exercise-induced ischemia were larger in patients with do wnsloping depression than inpatients with horizontal depression (P < . 02, P < .05). in patients with horizontal ST-segment depression, RMBF in ischemic areas and in surrounding areas increased by a similar amou nt(31% +/- 29% and 32% +/- 16%) with exercise. In patients with downsl oping ST-segment depression, RMBF was unchanged or decreased in ischem ic areas (10% +/- 24%) but increased in surrounding areas (46% +/- 27% ) with exercise. in healthy volunteers, RMBF increased in all areas (5 6% +/- 30%) with exercise. Conclusions Compared with horizontal change s in ST-segment morphology, downsloping changes may better indicate se vere ischemia and greater differences in the increase of blood flow wi th exercise in the ischemic myocardium and in the surrounding areas.