Kinetics and metabolism of 123I-BMIPP in canine stunned myocardium

Objective: Myocardial stunning has been proved to be associated with many clinical situations. No ideal approach was available for noninvasive diagnosis of myocardial stunning. The mismatched uptake of 123I-(15-(p-iodophenyl)-3(R, S)-methylpentadecanoic acid (BMIPP) and thallium was clinically demonstrated in stunned myocardium. Discrepant results from animal model, however, raise a question of the reliability in the use of BMIPP for diagnosis of myocardial stunning. Methods: A classic canine model of myocardial stunning was established. Regional uptake and retention of BMIPP and Tl were evaluated by SPECT imaging and tissue counting and were compared with regional myocardial blood flow (RBF) and wall thickening (WT). Regional metabolic parameters (including oxygen consumption, glucose and lactate utilization) were measured. Thin-larger chromatography (TLC) was used for the analysis of BMIPP and its metabolites. The kinetics of the extraction of BMIPP and its products from both stunned and non-stunned territories were compared. Results: A mismatched retention with higher BMIPP counts [(70 +- 6)%] than Tl[66 +- 6)%, P < 0.05] was found in stunned area on excised heart images. Though retention of BMIPP [(88.5 +- 6.0)%] and Tl[(85.4 +- 6.7)%] was matched well in stunned transmural myocardium, both BMIPP and Tl activity was greater than RBF [(70.4 +- 10.5)%, P < 0.001]. In stunned myocardium, Tl showed a good correlation with RBF (r = 0.67), but BMIPP did not (r = 0.11). Despite of insufficient oxidation and utilization of lactate, the release of BMIPP products and washout of tissue radio-activity from stunned myocardium increased significantly. No evidence of increased BMIPP back-diffusion was offered, since the proportion of intact BMIPP activity was always lower (though not significant) in the plasma from stunned territory. Conclusion: These results suggest that metabolic factors (especially washout of products) have a significant effect on retention of BMIPP in stunned myocardium, while retention of Tl is dependent mainly on RBF