ATRIAL SEPTAL DEFECT

The primary purpose of this paper is to present certain highly characteristic features of atrial septal defect that are either insufficiently well known or poorly understood: these include particularly the electrocardiographic appearances, the pressures in the right side of the heart, and the nature and significance of the second heart sound. It is generally agreed that the diagnosis of atrial septal defect is based mainly on the radiological findings. These have been well described by Assmann (1928), by Roesler (1934), and by Bedford, Papp, and Parkinson (1941), and are now well recognized-at least in advanced cases. The right auricle, right ventricle, and main pulmonary artery are dilated; the left and right branches of the pulmonary artery are unusually large and dense, and may pulsate with great vigour, while heavy vascular shadows mark the lung fields. In contrast, the aorta and left ventricle are hypoplasic (Fig. 1 and 2). McGinn and White (1933) and more recently Burrett and White (1945) agree with the authors cited above that a purely clinical diagnosis cannot be made with confidence, although certain features are suggestive: these include partial or complete arachnodactyly, relatively good health in childhood and adolescence, the frequent association of mitral valve disease, the rarity of bacterial endocarditis, the not infrequent occurrence of auricular fibrillation, a thrusting cardiac impulse associated with gross right ventricular dominance, a pulmonary systolic murmur often accompanied by a thrill, accentuation of the pulmonary second sound, a pulmonary diastolic murmur, and an audible third heart sound. Electrocardiograms in atrial septal defect may show tall P waves, slight prolongation of the P-R interval, right ventricular dominance or right bundle branch block (Bedford, Papp, and Parkinson, 1941). Historical details will be given more fully later. In recent years cardiac catheterization has been used with increasing frequency to prove the diagnosis, samples of blood obtained from the pulmonary artery, right ventricle, and right auricle containing appreciably more oxygen than samples from the vene cavx (Howarth et al., 1947). Angiocardiography has proved less helpful, for the shunt is normally from left to right auricle, and the contrast medium becomes so diluted that it does not show up well after returning to the left auricle from the lungs. It is true that diodone may pass through the defect from right to left, owing to the high pressure generated in the right auricle by the force of the injection, but this does not distinguish atrial septal defect from patent foramen ovale.