Addition of simultaneous dipyridamole infusion (SDInf) to maximal treadmill exercise (MTEx) enhances myocardial Tl-201 uptake without affecting exercise performance

Full text: Vasodilators are more potent than exercise for inducing coronary hyperaemia, while a maximal exercise test provides valuable clinical information. This provides a rationale for attempting to combine the two for myocardial perfusion imaging (MPI). We examined whether dipyridamole given during MTX significantly enhanced myocardial Tl-201 uptake or altered exercise performance. Twenty patients with low pretest likelihood of coronary artery disease, who could exercise well and were not receiving negative chronotropic agents, were randomly assigned to standard Tl-201 MPI using Bruce Protocol MTEx (n=10) or Bruce Protocol MTEx with simultaneous infusion of 0.56 mg/kg of dipyridamole (n=10). (Results given as mean ± s.d.; p values derived using a two tailed t-test). Both groups comprised four men and six women similar in age (56± 11 vs 59±10 years, p=NS) and weight (71±8 vs 72±11 kg, p=NS). There was no significant difference in exercise duration (7:10±2:17 vs 6:54±1:45 minutes), peak heart rate (164±10 vs 158±10 bpm) and rate-pressure product (312±57 vs 304±47). After background correction and standardization to administered Tl-201 activity, total myocardial counts measured on an anterior planar image obtained immediately post-exercise were 38% greater in the dipyridamole group (5.6±1.1 vs 7.7±1.2 kcounts/min/[MBq/kg], p<0.001). All subsequent SPECT Tl-201 scans were normal or showed only minor abnormalities. We conclude that SDInf significantly augments normal coronary hyperaemia over and above MTEx. Theoretically, this should enhance image quality for SPECT (higher counts) and sensitivity (defect to normal myocardial contrast). SDInf did not significantly impair exercise performance.Copyright (2000) The Australian and New Zealand Society of Nuclear Medicine Inc