Slow regional clearance of myocardial thallium-201 in the absence of perfusion defect: contribution to detection of individual coronary artery stenoses and mechanism for occurrence.

As a result of the "spatially relative" nature of perfusion defect analysis of stress-redistribution thallium-201 (201Tl) scintigrams, hypoperfused myocardial segments may not appear as perfusion defects but they may demonstrate a slow washout rate of 201Tl that can be analyzed in a "spatially nonrelative" manner. Quantitative analysis of perfusion defects and slow washout rate of 201Tl was performed on scintigrams from 116 consecutive patients with adequate exercise tests, defined as achievement of 85% or more of age-predicted maximum heart rate or development of angina or ST segment depression. A total of 232 diseased and 116 nondiseased vessels were found in the patients. Additional analysis of slow washout rate significantly (p less than .05) improved sensitivity for detection of disease in the left anterior descending (from 74% to 82%), left circumflex (from 40% to 61%), and right coronary arteries (from 78% to 90%) without significant loss of specificity. This improvement resulted from the additional detection of 32 of 232 (14%) diseased vascular distributions when the isolated slow washout rate of 201Tl was also determined. In nine of these 32, isolated slow washout rate was associated with another region with isolated slow washout rate in the contralateral myocardial segment. Coronary arteriography revealed similar degrees of stenosis in the vessels supplying these segment pairs. In 13 of 32 cases, a perfusion defect and a slow washout rate were found in the contralateral segment.(ABSTRACT TRUNCATED AT 250 WORDS)