Effects of dipyridamole-induced vasodilation on myocardial uptake and clearance kinetics of thallium-201.

Abstract

Myocardial thallium-201 (201T1) uptake and clearance after intravenous administration of dipyridamole (150 jig/kg) were determined in 12 open-chest anesthetized dogs with a partial coronary artery stenosis. 201TI (1.5 mCi) was injected intravenously and myocardial biopsy specimens were obtained 10 min, 60 min, and 2 hr after injection. Serial changes in 201.T1 activity in the normal zone and in the zone of partial stenosis were correlated with microsphere-determined regional blood flow and distal coronary pressure. Another nine dogs with equivalent stenosis not given dipyridamole before 201TI served as controls. In the 12 dogs given dipyridamole, 201TI activity at 10 min in the zone of stenosis was reduced to 42 ± 5% of initial normal zone activity (p < .001) and remained at 44 ± 3% of initial normal zone activity at 2 hr. There was a good correlation (.81) between the percent reduction in myocardial 201TI activity and the percent reduction of peak hyperemic flow as determined by measuring the percentage difference in peak coronary flow after a transient 10 sec occlusion under control and stenotic conditions. In contrast, 201TI clearance was rapid in the normal zone, with 201T1 activity decreasing to 55 ± 3% of initial normal zone activity by 2 hr. A redistribution pattern was produced because of the disparate clearance rates from hyperperfused and relatively hypoperfused myocardial regions. The relative 201TI defect decreased from 58% to 1 1% from 10 min to 2 hr. In the normal zone dipyridamole increased epicardial flow from 1.03 0.09 (SEM) to 3.52 0.36 ml/min/ g (p < .0001) and endocardial flow from 1. 19 ± 0.09 to 2.96 0.20 ml/min/g (p = .0001). In the zone of partial stenosis the increase in epicardial flow after dipyridamole was less marked (1.01 ± 0.10 to 1.55 + 0.15 ml/min/g; p = .009) and endocardial flow decreased (0. 84 + 0. 11 to 0.64 + 0.15 ml/ min/g; p = .04). Coronary perfusion pressure distal to the stenotic zone fell from 65 ± 3 to 50 ± 3 mm Hg after dipyridamole. In the nine control dogs with equivalent stenosis, 201TI uptake and washout were not significantly different in the stenotic zone compared with the normal zone. These data indicate that dipyridamole-induced vasodilation in the presence of a partial stenosis results in diminished uptake and delayed clearance compared with increased uptake and more rapid clearance in normally perfused myocardium producing an initial 201TI defect with delayed redistribution. Our data further demonstrate that the magnitude of the initial decrease in 201TI uptake after dipyridamole correlates well with the percent reduction in coronary flow relative to the peak hyperemic flow response. Circulation 68, No. 6, 1328No. 6, -1338No. 6, , 1983 SYMPTOM-LIMITED EXERCISE is routinely used in conjunction with thallium-201 (201T1) myocardial imaging for detection and evaluation of coronary artery disease. Adequate stress is essential, since coronary artery disease will reduce the reserve capacity of the stenotic vessel long before there is significant reduct...

Safety and Diagnostic Value of Intravenous Dipyridamole Thallium Scintigraphy in Patients with Suspected Coronary Artery Disease

“…Conversely, the stenosed coronary vessels are maximally dilated because of the autoregulatory mechanism and demonstrate no further increase in blood flow [8,12]. Since the initial myocardial distribution of Tl-201 is proportional to blood flow [1], DP administration will maximize the regional differences in Tl-201 uptake between zones of myocardium supplied by stenosed and normal coronary arteries [9,10].…”

“…Since the initial myocardial distribution of Tl-201 is proportional to blood flow [1], DP administration will maximize the regional differences in Tl-201 uptake between zones of myocardium supplied by stenosed and normal coronary arteries [9,10]. Furthermore, the clearance (washout) rate from normally perfused myocardium has been shown to be faster than that from ischemic myocardium following DP administration [12]. The difference in clearance rate will result in normalization (redistribution) of the initial defect, enhancing the scintigraphic detection of ischemia [13].…”

“…Under these circumstances, pharmacologically produced maximal coronary vasodilation with intravenous dipyridamole ([DP] Persantine; Boehringer-Ingelheim) is a better method [8][9][10][11][12][13].…”

Intrinsic washout rates of thallium-201 in normal and ischemic myocardium after dipyridamole-induced vasodilation.

“…Isotope separation and myocardial blood flow values were calculated according to methods previously described. 16 All myocardial samples were held 2 weeks before counting to permit decay of 201T1 activity to more appropriate levels. The counts per minutes recorded in each window for myocardial and reference blood samples were corrected for background activity as well as spill activity contributed by the isotopes of higher energy.…”

Dipyridamole thallium 201 imaging. How safe is it?

“…4 Blood is redistributed from the See p 1205 endocardial to the epicardial layers; this redistribution is referred to as intramural or transmural coronary "steal" and is characteristically associated with a fall in distal coronary perfusion pressure. These flow responses are not surprising, because dipyridamole acts by blocking the uptake of adenosine in red blood cells and endothelium, thereby increasing plasma levels and potentiating the activity of the endogenous vasodilator.…”