Clinical usefulness and safety of lung perfusion scintigraphy with 99mTc-MAA in the follow-up of children operated for transposition of the Great Arteries

Lung perfusion scintigraphy (LPS) can play a significant role during the follow up of congenital heart disease with peripheral pulmonary bed involvement, as in tetralogy of Fallot. After detecting by echocardiography sporadic lung perfusion disturbances in patients affected by transposition of the great arteries (TGA) we introduced LPS in the follow up of these patients. Materials and Methods: We have evaluated the clinical usefulness of 99mTc-labeled macroaggregated albumin (99mTc-MAA) LPS in 34 patients (age 0 - 222 months, median 21; M 25, F 9) treated for TGA during the first weeks of life (median age at intervention 14 days). Only 2 patients had history of pulmonary artery stenosis corrected during surgery. All patients were asympomatic (NYHA class 1) and off therapy. The standard follow up included clinical examination, ECG and echocardiography. LPS was performed using a weight-scaled dose of 99mTc-MAA, accordingly to the EANM Paediatric Commitee guidelines. The number of injected particles was similarly adjusted, using an adult reference dose of 300000. Patients were positioned on a gamma-camera equipped with a high resolution parallel-hole collimator, without sedation, using only mild physical constraint (Velcro straps, sand bags, etc.) when necessary. Each image was stored in a 256x256 matrix with 500 Kcounts at least. The right/left distribution was calculated as percentage of total lung activity, drawing lung ROIs on the posterior view. Definite hypoperfusion was defined as <40% and severe hypoperfusion < 30%. Results: A total of 52 scans were performed (9 patients had 2 or more studies), whithout adverse reactions. A definite (<40%) lung hypoperfusion was detetcted in 16/34 (47%) patients (left lung 11, right lung 5). Five out of 16 had a severe hypoperfusion (40%) after percutaneous angioplasty. Scintigraphic data modified the clinical management in 10/34 patients. Conclusions: The data confirm the safety of 99mTc-MAA LPS in the follow up of congenital heart disease. The prevalence of lung perfusion unbalance is quite high (47%) in this group of TGA patients and the severity threshold (<30%) has beeen reached in 1/3 of the affected subjects. Based on echocardiography and surgical history only a minority of them was suspected of having impaired lung perfusion, therefore it seems appropriate to introduce the LPS in the routine follow up. Further studies are needed to elucidate the pathogenesis and the long-term clinical significance of pulmonary blood flow abnormalities in these patients.