Cardiac MRA monitors pediatric heart surgery

MR angiography can successfully monitor children who have had arterial switch surgery for transposition of the great arteries. Researchers in Belgium suggest the technique could spare children x-ray exposure from repeated exams and the potential toxicity of iodinated contrast agents.

Arterial switch surgery involves the aorta, main pulmonary artery, coronary arteries, and aortic sinus. The midterm prognosis in these cases is good, with most complications and mortality occurring within the first year of life. But data are sparse about the natural history of coronary development in asymptomatic children as they grow.

Dr. Andrew M. Taylor and colleagues from Gasthuisberg University Hospital in Leuven used MRA to prospectively evaluate 16 asymptomatic subjects who had undergone arterial switch surgery for transposition of the great arteries. The mean age of the subjects was 10 years and all but one were awake during imaging (Radiology 2005;234:542-547).

The researchers assessed MR coronary angiography, late-enhancement MR imaging, global ventricular function, and regional wall motion. MRA helped identify the origin and course of the proximal coronary arteries in all 16 subjects, as compared with surgical findings.

Diagnostic-quality images of the coronary ostium and proximal coronary artery course occurred in 72% of the images of coronary arteries. This increased to 100% in subjects older than 11 years. Global left and right ventricular functions were preserved, with no regional wall abnormalities.

Patients older than 11 years needed no sedation or breath-holding. In the younger children, images were generally not of diagnostic quality. However, the researchers acquired excellent images from an eight-year-old boy under general anesthesia with intermittent suspended ventilation.

They found no unexpected areas of myocardial infarction, suggesting that patients who survive to this age did not have asymptomatic episodes of myocardial damage at the time of surgery.

In two patients with myocardial damage, the lesions were subendocardial, with maintained wall motion and known abnormalities of the coronary artery that supplied that territory.

A long-term concern regarding patients who have undergone arterial switch surgery for transposition of the great arteries is the lack of coronary ostia growth over time, with possible progression to coronary ostial stenosis or kinking of the proximal coronary arteries. Previous studies showed this can occur in asymptomatic individuals. The Belgian researchers saw no evidence of ostial coronary stenoses or proximal coronary artery kinking.

They concluded that larger scale cardiac MR comparative studies are appropriate. Such a long-term study in asymptomatic individuals may demonstrate that coronary artery complications are not the long-term problem that many have foreseen.