Intravenous Dipyridamole: Use in Thallous Chloride TL 201 Stress Imaging

An intravenous form of dipyridamole has been approved for cardiac stress testing with thallous chloride Tl 201 (201Tl) imaging. The procedure provides an alternative method for stress testing of patients who cannot perform strenuous physical exercise because of physical limitations or those in the immediate postinfarction period. Dipyridamole simulates the physiologic effects of physical exercise by increasing adenosine concentrations, which in turn increases coronary blood flow. Dipyridamole maximizes the differences in uptake of radioactive thallium in myocardial regions supplied by normal coronary arteries and those distal to stenosed arteries where blood flow is reduced. The sensitivity and specificity of dipyridamole-201Tl stress imaging for the detection of coronary disease are comparable to those of traditional exercise-201Tl stress testing. The intravenous dipyridamole usually is well tolerated, and the majority of adverse effects can be reversed with the administration of aminophylline.