[Radioisotopes for the study of right and left ventricular function in surgically treated Fallot's tetralogy]

Radio-nuclide angiography after surgical correction of tetralogy of Fallot (TOF) allows measurement of the ejection fraction, especially of the right ventricle, under basal conditions and on effort, parameters which are difficult to measure by other non-invasive methods. Twenty-two children with a mean age of 12.6 +/- 6.9 years who had undergone complete correction of TOF at a mean age of 6.7 +/- 3.8 years underwent Technetium 99m blood pool studies at equilibrium. The results were compared with those of a control group of children with a mean age of 10.2 +/- 3.3 years. No first passage studies were performed because the frequency of postoperative pulmonary regurgitation does not allow quantification of the shunt due to a possible residual ventricular septal defect. No significant difference was found between the patients and control subjects at rest: LV ejection fraction (66.7 +/- 11 p. 100 vs 63 +/- 7.7 p. 100), RV ejection fraction (50.3 +/- 7.2 p. 100 vs 54 +/- 14.8 p. 100). The response to effort of the right and left ventricles depends on the type of exercise. The LV ejection fraction increased normally whilst the RV ejection fraction showed a lot of individual variation. Equilibrium radionuclide angiography was also used to calculate the ratio of right to left end diastolic ventricular volumes. This ratio indicates the degree of RV diastolic overload when LV diastolic volumes are normal, which was the case in our series. The study group showed a significant increase in this ratio compared to control subjects (1.94 +/- 0.65 vs 1.2 +/- 0.23). Exercise radionuclide imagery should provide more accurate assessments of the surgical results and prognosis of these children providing standardised protocols are used. These investigations are best performed in patients over 15 years old, so as to avoid the technical difficulties related to small size. Resting studies are possible at all ages.