Background: Microvascular dysfunction has been proposed as the most likely mechanism of the coronary slow flow phenomenon (CSFP). Objective: To determine the effects of isosorbide dinitrate and nicorandil on the CSFP. Methods: Changes in thrombolysis in myocardial infarction (TIMI) frame count following the intracoronary administration of isosorbide dinitrate and nicorandil were assessed in 11 patients with the CSFP. Results: After the administration of isosorbide dinitrate, the median TIMI frame count decreased to 32 (range 20-60) [p = 0.003], which was lower than that of the control [43 (29-73)]. The count decreased further to 25 (12-34) [p = 0.041] after the administration of nicorandil. The count after the subsequent administration of contrast medium was increased to 32 (20-49) [p = 0.03]. Conclusions: These angiographic findings indicate that the intracoronary administration of nicorandil is superior to isosorbide dinitrate with regard to improving the CSFP. These findings suggest that microvascular spasm is the main factor in the pathogenesis of the CSFP.
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