TL-201 MYOCARDIAL SCINTIGRAPHY AND LEFT-B UNDLE-BRANCH BLOCK - RELATIVE VALUES OF EXERCISE AND DIPYRIDAMOLE TESTING

Stress Thallium 201 myocardial scintigraphy in patients with left bund le branch block often shows reversible septal perfusion defects even i n the absence of coronary artery disease. This phenomenon seems more c ommon when the patients have tachycardia. With the working hypothesis that dipyridamole stress testing, which does not greatly increase the heart rate, would be more appropriate than exercise stress testing to unmask coronary artery disease in this condition, the authors compared the results of two Thallium 201 scintigraphies performed after exerci se and then after dipyridamole under the same conditions three weeks l ater, in 67 patients with complete left bundle branch block. Scintigra phy showed one or more reversible perfusion defects in 64/67 patients after exercise but only 32/67 patients after dipyridamole (p < 0.001). There was poor uptake in the septal region in 59 patients (88 %) afte r exercise and in 25 patients (37 %) after dipyridamole (p < 0.001). T he specificity was evaluted in 23 patients estimated to have no corona ry artery disease. If only unequi vocal perfusion defects were conside red, the specificity after dipyridamole was higher than that after exe rcise, increasing from : 35 % to 83 % for septal defects (p < 0.0 1); 65 % to 96 % for anterior wall defects (p < 0.05); 61 % to 87 % for in ferior wall defects (p < 0.05); 57 % to 91 % for apical defects (p < 0 .01); 17 % to 83 % overall (p < 0.001). Lower values but with a compar able difference were observed when all forms of hypofixation (even min imal) were taken into account. The sensitivity of the two methods eval uated in 14 coronary patients was equivalent (100 % after exercise 93 % after dipyridamole) and the two methods were equally valuable for pr edicting the site of stenosis on the three main coronary arteries. The authors conclude that in patients with complete left bundle branch bl ock, dipyridamole stress testing would seem to be superior to exercise stress testing when diagnostic Thallium 201 myocardial scintigraphy i s performed. The sensitivity and specificity of scintigraphy is then c omparable to the values observed in all other patients.