Non-invasive assessment of isolated atrial defects.

This study attempts to predict the size of shunt in secundum atrial septal defects by non-invasive M-mode echocardiography.The areas under the excursions of the mitral and tricuspid valves were measured with a sonic digitiser and the ratio of these areas compared with the shunt size as obtained at c'atheterisation.The relation between the mitral and tricuspid valve areas in patients with atrial septal defect is significantly different from that in healthy subjects.There is a significant positive correlation be- tween the ratio of mitral and tricuspid valve areas and the shunt size.Solitary secundum atrial septal defect with a left to right shunt and no other congenital abnormality or complication is a common condition.Clinical hall- marks of atrial septal defect are well recognised, and by other simple non-invasive methods it is usually possible to isolate this condition.In the age range 3 to 30 years, complications are rare and, with the possible exception of anomalous pulmonary venous drainage, associated congenital abnormalities and variants are recognisable.The assessment of shunt size is the, if questionable, indication for cardiac catheterisation.The size of high pressure left to right shunts- ventricular septal defects and persistent ductus arteriosus-has been successfully predicted by the aortic/left atrial ratio as measured on the M-mode echocardiogram.I 2 This technique has also been used in controlling the size of the ductus as well as monitoring postoperatively closures of ventricular septal defect.The patients with atrial septal defect, however, show no left atrial enlargement because the volume overload is immediately shunted into the right atrium and the aortic/left atrial ratio becomes invalid.Two typical characteristics of atrial septal defect suggest a possible method of assessing the size of the left to right shunt.The first is that the tricuspid valve and mitral valve are both easily shown by M-mode echocardiography.Secondly, it has been shown that the stroke volume is related to the area beneath the mitral valve CUSpS.3We have based this paper on the hypothesis that the pattern of mitral valve and tricus- pid valve echocardiograms would reflect the quantity