Acute Effects of Oral Isosorbide Dinitrate on Exercise Thallium-201 Myocardial Imaging in Patients with Stable Angina Pectoris

Abstract

The acute effects of oral isosorbide dinitrate (ISDN) on myocardial perfusion was compared to placebo (PLC) using thallium-201 myocardial perfusion scintigraphy with bicycle ergometry in 31 patients with a history of stable angina pectoris and an exercise-induced thallium defect with resolution at rest, 31.7 ± 3.4 (SEM) days prior to an on-therapy stress test. Following a dose-finding trial, 15 patients were randomized to ISDN and 16 to PLC. The two patient groups were not significantly different at baseline. One hour following ISDN or PLC the patients undwerwent exercise thallium-201 stress testing. Exercise duration, total work load and peak double product were similar in the 2 groups of patients at both stress tests. Qualitative comparisons of the thallium images did not reveal any differences between the 2 groups. Also quantitative comparisons of thallium images did not reveal differences between the two groups in the regions of highest and lowest count rates per pixel, or percent defect rate of perfusion (DRP%) of the defect areas [DRP% = 1 - (counts of the area with defect/counts of the area with highest count density)] during both tests. However, DRP% in the ISDN group following exercise was significantly lower after treatment (18.5 ± 3.1)than before (27.1 ± 2.3; p < 0.001 ), while the corresponding values for the PLC were not statistically different (25.2 ± 3.2 and 27.4 ± 1.4). Also although redistribution produced a statistically significant decrease in DRP% in comparison with the post-exercise images in the pretreatment and treatment phases of the PLC group and the pretreatment phase of ISDN group, the on-treatment DRP% change for the ISDN group was not statistically different (18.5 ± 3.1 vs. 12.4 ± 2.6). These results suggest that improvement in perfusion or more homogeneous distribution of coronary flow during exercise was effected by the oral administration of ISDN. However, this drug did not have a similar effect on the redistribution images. This reduction in the difference in count density between the areas with the highest counts and the ones identified as defects should be attributed to improvement in the rate of coronary blood flow to the originally poorly perfused regions, since the external work load and double product (reflecting myocardial oxygen demands) did not change between the 2 tests.