The Effect of Ischemia

To determine the effect of ischemia on myocardial clearance of thallium-201 (201TI), we studied 12 dogs with ischemia produced after the injection of Tl. TI was given I.V. 10 minutes before left anterior descending (LAD) coronary artery ligation. 85Sr-microspheres (MS) were administered 5 minutes later, and control biopsies were obtained from the myocardium. The LAD was tied and repeat biopsies obtained from the ischemic zone (IZ) and normal zone (NZ) 15 minutes and 2 hours later. 46Sc-MS were given just before the final biopsy. Tl activity in the IZ was not significantly different from that in the NZ either before LAD occlusion or 15 minutes and 2 hours later. TI clearance at the end of 2 hours was not significantly different (27 ± 5% vs 28 ± 5%, IZ vs NZ respectively) between the two zones. The half-time of TI clearance from both the IZ and NZ was calculated at 4.5 hours (consistent with previously reported normal values). This occurred despite a decrease in regional myocardial blood flow to 24 ± 6% of control (P < 0.01) in the IZ and an increase to 147 ± 14% of control (P < 0.01) in the NZ during the study. We conclude that myocardial ischemia does not alter the normal rate of TI clearance from the myocardium.