Abstract |
The noninvasive nature of the radionuclide
angiocardiography provided a useful approach for the
evaluation of left-to-right cardiac shunts (LRCS).
While the qualitative information can be obtained by
inspection of serial radionuclide angiocardiograms, the
quantitative information of radionuclide
angiocardiography can be obtained by the analysis of
time-activity curves using advanced computer system.
The count ratios metod and pulmonary-to-systemic flow
ratio (QP/QS) by gamma variate fit rnethod were used to
evaluate the accuracy of detection and localization of
LRCS. One hundred and ten time-activity curves were
analyzed. There were 46 LRCS (atrial septai defects 11,
ventricular septal defects 22, patent ductus arteriosus
13) and 64 normal subjects. By compute:r analysis of
time-activity curves of the right atriurn, ventricle
and the lungs separately, the count ratios modiiied by
adding the rnean cardiac transit time were calcuiated
in each anatomic site. In normal subjects the mean
count ratios in the right atrium, ventricle and lungs
were 0.24 on average. In atrial septal defects, the
count ratios were high in the right atrium, ventricle
and lungs, whereas in ventricular septal defects the
count ratios were higher only in the right ventricle
and lungs. Pateot ductus arteriosus showed normal count
ratios in the heart but high count ratios were obtained
in the 1ungs. Thus, this count ratios method could be
separated norma! from those with intracardiac or
extracardiac shunts, and moreover, with this method the
localization of the shunt level was possible in LRCS.
Another method that could differentiate the
intracardiac shunts from extracardiac shunts was
measuring QP/QS in the left and right lungs. In patent
ductus arteriosus, the left lung QP/QS was higher than
those of the right lung, whereas in atrial septa!
defects and ventricular septal defects QP/ QS ratios
were equal in both lungs. From this study, it was found
that by rneasuring QP/QS separately in the lungs,
intracardiac shunt could be differenciated from
ext.racardiac shunts. |