SIGNIFICANCE OF DOWNSLOPING ST-SEGMENT DEPRESSION INDUCED BY LOW-LEVEL EXERCISE IN SEVERE CORONARY-ARTERY DISEASE - ASSESSMENT WITH MYOCARDIAL-ISCHEMIA AND COLLATERAL PERFUSION

Exercise-induced downsloping ST-segment depression is a common manifes tation of severe myocardial ischemia. Although greater downsloping ST- segment depression is suspected to indicate more ses ere ischemia, its exact relationship to regional myocardial blood flow (RMBF) has not y et been clarified. We investigated the relationship between the magnit ude of downsloping ST-segment depression and exercise-induced changes in RMBF and collateral perfusion. Nitrogen-13 ammonia positron emissio n tomography was performed in 6 healthy volunteers and 72 patients wit h angiographically proven coronary artery disease. The left ventricle was divided into 11 regions of interest, and RMBF in each region was m easured at rest and during low-level supine bicycle exercise, Downslop ing ST-segment depression of 0.1 mV or more at 80 milliseconds after t he J point was accepted as significant, Low-level exercise induced dow nsloping depression of 0.1 to 0.2 mV in 10 patients (group D-1) and do wnsloping depression of 0.2 mV or more in 8 patients (group D-2). Mult ivessel disease was common in both group D-1 (80% of patients) and gro up D-2 (88% of patients). Collateral circulation was significantly mor e frequent in group D-1 (90%) than in group D-2 (13%, p < 0.01). Ische mic areas were larger and cardiac function was worse in group D-2 than in group D-1. The RMBF increased sufficiently in all regions (56 +/- 30%) with exercise in the healthy group. In group D-1, RMBF was unchan ged or decreased in ischemic areas (10 +/- 23%) but increased sufficie ntly in surrounding areas (50 +/- 32%), In group D-2, RMBF was unchang ed in ischemic areas (17 +/- 24%) and increased insufficiently in surr ounding areas (41 +/- 21%). Therefore, exercise-induced downsloping ST -segment depression of 0.1 to 0.2 mV may reflect an underlying change in blood flow in viable myocardium with collateral perfusion, and down sloping depression of 0.2 mV or more may reflect more severely impaire d myocardium without collateral perfusion.