(201)Tl and (99m)Tc-MIBI retention in an isolated heart model of low-flow ischemia and stunning: evidence of negligible impact of myocyte metabolism on tracer kinetics.
It is not known whether cellular metabolic disorders play a role in the decreased tracer uptake that is documented by conventional SPECT during low-flow ischemia or stunning. This study sought to determine the impact of low-flow ischemia and stunning on the kinetics of (201)Tl and MIBI across the plasma membrane of myocytes.


METHODS
The global myocardial retention (Rf) of (201)Tl and MIBI was determined in isolated working hearts from rabbits, perfused with red blood cell-enhanced solution. Experiments were performed in normoxia, with physiological values of coronary flow (N; n = 16); in low-flow ischemia, with a >50% reduction of coronary flow and a > or =20-mm Hg fall in systolic left ventricle pressure (L; n = 15); and in stunning, with 15 min of acute ischemia followed by reperfusion (S; n = 15). Concentration ratios across the plasma membrane of myocytes were also determined for both tracers and expressed as Ci/Cc, where Ci is interstitial activity determined with microdialysis, and Cc is activity from cellular space determined from Rf and Ci values.


RESULTS
There was a slight increase in average values of Ci/Cc in ischemia, but not in stunning, for (201)Tl (L, 0.011 +/- 0.006 vs. N, 0.006 +/- 0.004 [P < 0.05]; S, 0.007 +/- 0.004 vs. N [not significant]) and for MIBI (L, 0.011 +/- 0.008 vs. N, 0.005 +/- 0.004 [P < 0.05]; S, 0.005 +/- 0.003 vs. N [not significant]). Moreover, ischemia and stunning had no deleterious effects on the average values of global myocardial retention for (201)Tl (L, 0.63 +/- 0.09 vs. N, 0.50 +/- 0.14 [P < 0.05]; S, 0.59 +/- 0.10 vs. N [P < 0.05]) or for MIBI (L, 0.45 +/- 0.10 vs. N, 0.31 +/- 0.09 [P < 0.05]; S, 0.41 +/- 0.12 vs. N [P < 0.05]). In fact, these values were significantly enhanced in the 2 situations.


CONCLUSIONS
The kinetics of (201)Tl and MIBI across the plasma membrane of myocytes were affected only poorly by low-flow ischemia and not at all by stunning, without any deleterious effects on myocardial retention of both tracers. During low-flow ischemia or stunning, therefore, the information provided by (201)Tl or MIBI SPECT is expected to depend on myocardial perfusion but not on cellular metabolic disorders.
Ayalew
Adey
A
Department of Nuclear Medicine, Laboratory of Experimental Surgery, Faculty of Medicine, UPRES EA 2403, CHU-Nancy, 54500 Vandoeuvre, France. aayalew@yahoo.com
Marie
Pierre-Yves
PY
Menu
Patrick
P
Mertes
Paul-Michel
PM
Audonnet
Sandra
S
Jouan
Valérie
V
Olivier
Pierre
P
Karcher
Gilles
G
Ungureanu-Longrois
Dan
D
Bertrand
Alain
A
D000818:Animals; D001783:Blood Flow Velocity; D001794:Blood Pressure; D003326:Coronary Circulation; D066298:In Vitro Techniques; D017551:Microdialysis; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging* / Q000378:metabolism; D017682:Myocardial Stunning / Q000000981:diagnostic imaging* / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption; D011817:Rabbits; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D017256:Technetium Tc 99m Sestamibi / Q000493:pharmacokinetics*; D013794:Thallium Radioisotopes / Q000493:pharmacokinetics*
D019275:Radiopharmaceuticals; D013794:Thallium Radioisotopes; D017256:Technetium Tc 99m Sestamibi