A mobilidade do Septum primum não depende do diâmetro do forame oval em fetos normais
Arquivos Brasileiros de Cardiologia
304 In fetal life, the septum primum acts as a valve to close the foramen ovale when atrial contraction occurs. In diastole, it protrudes within the left atrium, enabling maximal opening and flow from right to left. This protrusion is used as a reference to identify the left atrium (LA) in fetal echocardiography 1,2 . In previous studies, the mobility of the septum primum, its evolvement during intrauterine life 3 , and its correlation with the presence of atrial extrasystoles 4,5 were
... s 4,5 were assessed. To quantify the excursion of the septum primum during the cardiac cycle, an index that correlates its maximal excursion with the left atrium diameter was created, the so-called "excursion index" (EI). A previous study 6 showed that the excursion index is decreased in fetuses with ventricular septal hypertrophy secondary to maternal diabetes after 32 weeks of gestational age. An inverse correlation was present between the excursion index and interventricular septal thickness, suggesting that the excursion index could be used as a more suitable index for ventricular diastolic function than those usually accepted, since it was shown a more accurate inverse correlation with interventricular septal hypertrophy than the atrioventricular flows. Another previous study has already demonstrated that, during fetal breathing, the excursion index of the septum primum is significantly increased; this finding was explained by an increase in left ventricular distensibility due to respiratory movements 7 . Therefore, excursion of the septum primum depends on multiple factors, and its correlation with the foramen ovale size has not been studied. The present study was designed to test the hypothesis that a correlation exists between the foramen ovale diameter and the maximal excursion of the septum primum in normal fetuses. Methods This was a noncontrolled, transversal study, assessing 102 fetuses without structural or functional abnormalities of the heart; mothers had no risk factors for heart disease. Fetal echocardiography being performed sequentially from 20 weeks of gestation through term, in a specialized center of Fetal Cardiology. We excluded from the study fetuses with anatomical or functional abnormalities of the heart or any other organs and systems; fetuses whose mothers had systemic disease or risk factors for fetal heart disease; those in which it was impossible to obtain a suitable echocardiographic window; and gestational age below 20 weeks. Objective To test the hypothesis that a correlation exists between the maximum foramen ovale diastolic diameter and the excursion index (EI) of the septum primum in normal fetuses. Methods One hundred and two normal fetuses with gestational ages ranging from 20 to 40 weeks were submitted to echocardiography. The foramen ovale diameter and the "maximal excursion" of the septum primum were measured in a 4-chamber view. The data were analyzed by Pearson's correlation coefficient. Results The mean foramen ovale (FO) diameter was 5.06 ± 1.29 mm; the maximal excursion of the septum primum was 5.42 ± 1.41 mm; the left atrium diameter 11.47 ± 2.76 mm; the septum primum "excursion index" was 0.48 ± 0.09. Mean FO/EI ratio was 11.35 ± 3.94 mm. No FO/EI correlation (r = -0.03) existed, and a weak foramen ovale/left atrium correlation (r = 0.31) was observed, as well as a weak foramen ovale/excursion of septum primum correlation (r = 0.21). Conclusion Septum primum mobility does not depend on the foramen ovale diameter in normal fetuses, suggesting that the modifications of its diastolic displacement is not influenced by the size of the interatrial opening.