RESIDUAL TL-201 ACTIVITY IN IRREVERSIBLE DEFECTS AS A MARKER OF MYOCARDIAL VIABILITY CLINICOPATHOLOGICAL STUDY

Background The objective of the present study was to characterize the relation between the residual Tl-201 activity in irreversible perfusio n defects and the extent of irreversible myocardial damage indicated b y the volume fraction of myocardial interstitial fibrosis in patients with chronic coronary artery disease. Methods and Results Stress plana r Tl-201 scintigraphy with tracer reinjection at rest was performed in 37 patients with greater than or equal to 75% stenosis of the left an terior descending coronary artery, and anteroseptal Tl-201 activity wa s quantified by computer-assisted placement of regions of interest fro m the serial myocardial images. During coronary artery bypass grafting (performed within 6+/-3 weeks after scintigraphy), two transmural bio psy specimens were taken from the anterior wall of the left ventricle and the amount of interstitial fibrosis was assessed by use of light m icroscopic morphometry. A wide spectrum of interstitial fibrosis was o btained, ranging from 15 vol% to 60 vol%. Interstitial fibrosis was si milar in patients with reversible (n=11) or irreversible (n=15) tracer defects in conventional stress-redistribution images. However, inters titial fibrosis was significantly lower in patients who had enhanced r egional Tl-201 activity after tracer reinjection compared with those w ho did not have enhancement of tracer activity after reinjection (28+/ -8 vol%, n=7, versus 41+/-12 vol%, n=8; P=.031). The correlation betwe en relative poststenotic Tl-201 activity and interstitial fibrosis aft er tracer reinjection was significantly improved compared with convent ional redistribution images (r=-.622 versus r=-.851, n=15; P<.01). Con clusions The present data demonstrate that the level of regional Tl-20 1 activity in redistribution and, in particular, reinjection images is significantly related to the mass of preserved viable myocytes in pos tstenotic left ventricular myocardium. Therefore, the residual Tl-201 activity provides information about viability within irreversible perf usion defects and may itself serve as marker of myocardial viability.