Dipyridamole versus intracoronary injection of contrast medium for the evaluation of coronary reserve in man: A comparative study

Abstract Coronary reserve can be assessed by the ratio of coronary blood flow after “maximum” vasodilation to control flow. The intravenous infusion of dipyridamole (0.56 mg × kg−1) is considered to elicit maximum coronary vasodilation. The present study was designed to compare coronary flow and resistance responses to intravenous dipyridamole and intracoronary injection of contrast medium (ioxaglate), this latter technique being frequently used in digital radiology to stimulate hyperemia. The comparison was performed in seven normal patients, nine patients with coronary artery disease, and 16 patients with dilated cardiomyopathy. Coronary flow reserve was calculated as the ratio of peak flow after dipyridamole or contrast medium to control flow, and coronary resistance reserve was calculated as the ratio of minimal to control coronary resistance after each stimulus. Although flow reserve after dipyridamole was approximately twice that obtained after contrast medium in the normal group (4.01 ± 0.56 vs 2.02 ± 0.24) there was a close and linear relationship between coronary flow and resistance reserve estimated by both techniques (r = 0.846, p < 0.001 for flow reserve ratios, and r = 0.844 p < 0.001 for resistance reserve ratios). However, contrast‐induced hyperemia identified 13/25 (52%) of patients with coronary artery disease or dilated cardiomyopathy as having a reduced flow reserve, while dipyridamole revealed a restrained coronary flow reserve in 20/25 (80%) of these patients. Similar proportions were obtained when using coronary resistance reserve (56% for contrast vs 80% for dipyridamole). Thus, although contrast medium and dipyridamole provide closely correlated values of coronary flow and resistance reserve, a better separation between normals and patients is achieved after dipyridamole. These results should be considered in the estimation of coronary reserve by means of digital angiography and contrast agents, since the obtention of maximum coronary blood flow appears as a prerequisite for an adequate evaluation of the human coronary circulation functional status.