Sn. Weindling et al., MYOCARDIAL PERFUSION, FUNCTION AND EXERCISE TOLERANCE AFTER THE ARTERIAL SWITCH OPERATION, Journal of the American College of Cardiology, 23(2), 1994, pp. 424-433
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.