MYOCARDIAL PERFUSION, FUNCTION AND EXERCISE TOLERANCE AFTER THE ARTERIAL SWITCH OPERATION

Objectives. This study nas conducted to determine the prevalence of my ocardial perfusion abnormalities at rest and exercise and to assess ex ercise capacity in children after the arterial switch operation. Backg round. There have been sporadic reports of myocardial ischemia or sudd en death in children after the arterial switch operation for transposi tion of the great arteries, possibly related to inadequate coronary pe rfusion due to kinking or stenosis of the translocated coronary arteri es. Methods. Myocardial perfusion at rest and peak exercise was assess ed using the scintigraphic agent technetium-99m methoxy-isobutyl isoni trile (sestamibi). Exercise capacity was determined with a modified Br uce protocol. Ambulatory electrocardiographic (ECG) Holter monitoring was performed. Ventricular function, contractility and wall motion wer e assessed echocardiographically. Results. Twenty-three children (aged 4.2 to 7.9 years) underwent evaluation. Abnormalities were found on t he rest perfusion scans in 22 children (95.6%). The left ventricular m yocardium was divided into 13 segments for analysis. Of 299 rest segme nts, 225 (75.3%) were normal, 11 (3.7%) showed mild defects, 45 (15%) moderate defects and 18 (6%) severe defects at rest. At peak exercise, 237 segments (79.3%) were normal, 24 (8%) showed mild defects, 33 (11 %) moderate defects and 5 (1.7%) severe defects. Compared with rest st udies, myocardial perfusion grade at exercise was unchanged in 246 seg ments (82.3%), improved in 42 (14%) and worsened in 11 (3.7%). All pat ients had normal exercise tolerance without symptoms or ischemic ECG c hanges. No ventricular tachycardia was seen on Holter monitoring. All patients had a shortening fraction greater than or equal to 27%. Left ventricular contractility was normal in 12 children in whom it was ass essed. Regional wall motion was normal in 17 children with adequate ec hocardiographic images for this analysis. Conclusions. Myocardial perf usion scan abnormalities assessed by technetium-99m sestamibi are comm on after an arterial switch operation. These abnormalities are of unce rtain clinical significance and generally lessen with exercise. The no rmal exercise tolerance without symptoms or ECG changes suggests that myocardial perfusion is adequate during the physiologic stress of exer cise in children up to 8 years after an arterial switch operation.