Dipyridamole and exercise SPET provide different estimates of myocardial ischaemic areas: role of the severity of coronary stenoses and of the increase in heart rate during exercise

In patients unable to perform a maximal exercise test, dipyridamole single- photon emission tomography (SPET) has a higher capacity than exercise SPET to detect coronary artery disease (CAD). However, in patients with myocardi al ischaemia who are able to perform a maximal exercise test, it is not kno wn whether these two tests may be equally used to assess the areas of myoca rdial ischaemia. This study was aimed at comparing the results provided by dipyridamole and exercise SPET in CAD patients with documented exercise myo cardial ischaemia, Forty CAD patients who had undergone exercise thallium-2 01 SPET and who had myocardial ischaemia documented by an unequivocally pos itive exercise test underwent an additional Tl-201 SPET study after dipyrid amole infusion and low-level (40 W) exercise. The extent of defects was com pared between the two tests and predictors of discrepant results were sough t among data from exercise testing and coronary angiography. The extent of SPET defects was equivalent between the two tests in only 11 patients (28%) , larger defects being observed with exercise in 18 [average difference: 12 %+/-5% of left ventricle (LV)] and with dipyridamole in 11 (average differe nce: 15%+/-11% of LV). The best in dependent predictors of discrepancies be tween the two tests were: (1) increase in heart rate at exercise SPET, with defects being smaller at exercise than after dipyridamole in none of the p atients with an increase >60 bpm (0/14), but in 42% of the others (11/26; P =0.004); and (2) an ischaemic territory related to a <70% coronary stenosis , for which SPET defects were always induced at exercise (10/10) but in onl y 30% (3/10) with dipyrida mole (P=0.0004). Exercise and dipyridamole SPET provide different estimates of myocardial ischaemic areas. Dipyridamole all ows the unmasking of perfusion abnormalities in patients who have low incre ases in heart rate at exercise SPET. However, dipyridamole is also much les s efficient at inducing perfusion abnormalities in the ischaemic areas supp lied by coronary stenoses of intermediate severity at rest angiography.