Efficacy of 15-(123I)-p-iodophenyl pentadecanoic acid (IPPA) in assessing myocardial metabolism in a model of reversible global ischemia

Abstract

In a canine model of reversible global ischemia, the residual quantity of ¹²³I was assessed following a bolus injection of 15-p-(¹²³I)-iodophenyl pentadecanoic acid (¹²³I-IPPA). This technique was used to assess changes in free fatty acid metabolism following the utilization of three cardioplegic formulations. Cardioplegic arrest was initiated with Tyers' iso-osmolar (IO) solution (Group A); IO+superoxide dismutase (SOD) (Group B) and IO+allopurinol (Group C). Pre and post operative scanning were completed with 2–5 mCi ¹²³I-IPPA. Clearance was assessed by IPPA time activity curve analysis generating t _1/2 (half lives in min) for the early and late phases of the curve. The assessment between groups demonstrated that the elimination of ¹²³I-IPPA products (early phase) was faster from the lateral wall in groups B and C versus group A (14±12 min, 13±9 min and 24±10 min, respectively). The elimination of IPPA (late phase) was also faster from the lateral wall in groups B and C when compared to group A (240±270 min, 132±85 min and 416±238 min). Examining the changes between control and postoperative values for each area of the left ventricle within each group demonstrated no significant, changes for groups B and C. Group A, however, demonstrated significantly increased t _1/2 values for the lateral wall (early and late phases) and the apical wall (late phase). From this study it can be concluded that following 2 h of reversible global ischemia and reperfusion, the assessment of turnover of ¹²³I-IPPA can be used to differentiate the effectiveness of various cardioplegic formulations. It appears that cardioplegic solutions supplemented with allopurinol and SOD (groups B and C) may be better able to protect myocardial fatty acid metabolism compared to Tyers' iso-osmolar solution (group A).