INFLUENCE OF ANATOMIC CORRECTION FOR TRANSPOSITION OF THE GREAT-ARTERIES ON MYOCARDIAL PERFUSION - RADIONUCLIDE IMAGING WITH TC-99M 2-METHOXY ISOBUTYL ISONITRILE

Objectives. We sought to determine the incidence of late perfusion def ects attributable to coronary artery mobilization in patients undergoi ng anatomic correction for complete transposition of the great arterie s. Background. Anatomic correction (arterial switch procedure) is curr ently the surgical treatment of choice for complete transposition. Fro m its conception, there has been concern about the impact on myocardia l perfusion of the coronary artery mobilization and reimplantation inv olved in the correction. Previous studies have demonstrated myocardial perfusion defects in patients after correction, although a causal rel ation between coronary mobilization, and perfusion abnormality has not been established. Methods. In a case-comparison study designed to tes t this hypothesis, 29 children underwent imaging with technetium-99m 2 -methoxy isobutyl isonitrile (technetium-99m mibi). Ten had undergone anatomic correction (arterial switch group; interval from operation 6. 9 +/- 1.42 years [range 4.9 to 9.1]); 9 had required noncoronary open heart surgery for other cardiac lesions (postbypass group; interval fr om operation 5.6 +/- 3.6 years [range 1.0 to 13.25]); and 10 had had n o surgical procedure (control group). The latter group comprised child ren,vith atrial or ventricular septal defects who required a radionucl ide study for shunt calclation. Planar studies were performed in all 2 9 children, and additional tomographic acquisition was achieved in 25, To assess reversibility of perfusion defects both an exercise and a r est planar study were performed in the arterial switch group. Results. Perfusion abnormalities were observed in seven of the nine children i n the postbypass group and in all 10 children in the arterial switch g roup. The frequency of perfusion defects in these two groups was simil ar, with at least 25% of the tomographic segments reported being abnor mal. The control group had significantly fewer defects than the other two groups (p = 0.02), with only 8% of the tomographic segments judged to be abnormal. In all except one patient in the arterial switch grou p, the segments reported as abnormal on the planar exercise study were either abnormal or equivocal on the rest study, indicating a fixed ab normality. Conclusions. Although the precise etiology of these perfusi on abnormalities cannot be defined from this study, these data suggest that their origin is related more to the insult of open heart surgery itself than to the coronary manipulation involved in the arterial swi tch procedure. The functional importance requires further study.