Effect of age on pressure-flow dynamics in secundum atrial septal defect.

The first descriptions of the haemodynamic events in isolated atrial septal defect date back to the 1940s,I-9 yet a complete understanding of the precise flow patterns across the defect remains elusive. This is partly because of the complex and varying pressure and volume characteristics of the atria themselves, even with an intact septum, and partly because attempts to time and quantify the components of the interatrial shunt with available techniques of investigation have produced conflicting results. Two papers in this issue draw attention once more to the vagaries of this subject.I0 11 Both indicate inter alia that haemodynamic patterns change with age or duration of left to right shunting, and appreciation of this fact may help explain the disparate interpretations of the variable interatrial pressure-flow dynamics in atrial septal defect. Galve et al confirm that a right to left shunt occurs in an appreciable number of patients (15%),10 an observation first described as "cyanose tardive" by Bard and Curtillet in 1889,12 and subsequently demonstrated by peripheral'3 or central4679 14-16 oximetry, angiocardiography,17 18 or by dye dilution,'5 17 fibreoptic catheter,'9 or echocardiographic20 and intracardiac Doppler2l techniques. The reported incidence of right to left shunting varies from 14%22 to 1000/o.17 Galve et al show that this phenomenon is not associated with increased right atrial, right ventricular, or pulmonary artery pressures.'0 Although a right to left shunt has been found in cases of atrial septal defect in infancy9 and childhood,9 23 Gault et a124 and Dexter,'6 in the 1955 St Cyres lecture, also emphasise that this event occurs predominantly in older patients. Parikh et all" have approached the haemodynamic conundrum from the viewpoint of atrial pressure wave morphology and show that the alteration of the normal right atrial wave form ("a" > "v" wave) to a pattern of a dominant "v" wave ("v" > "a"),so called