The tilted left anterior oblique position in the study of congenital cardiac anomalies.

Abstract

Selective cineangiocardiography is widely used for the demonstration of congenital cardiac anomalies. Selective opacification of a cardiac chamber is performed after a diagnosis has been proposed or established by physical examination, radiographic and fluoroscopic examination of the chest, and study of data derived from external electrocardiography and cardiac catheterization. The selection of the injection site is determined by (a) the diagnosis established from the data and (b) the ability to introduce a catheter into the desired chamber. The roentgenographic positions chosen for selective angiocardiography depend upon the type of available equipment and the nature of the presumed cardiac anomaly. In the use of biplane rapid film changers, Kjellberg et al. (2) first called attention to the advantages and disadvantages of conventional positions for examination of congenital cardiac anomalies. Because of the complexities of cardiac anatomy, these investigators experimented with various positions of the patient. In addition to rotating the patient, Kjellberg tilted the x-ray tube so that the atrial and ventricular septa could be optimally outlined. Routine use of this maneuver was abandoned because of distortion projected on the biplane angiocardiograms. Kjellberg, therefore, recommended conventional postero-anterior and lateral projections for examination of virtually every cardiac lesion. These projections are the usual ones when biplane rapid film-changers are employed. On the other hand, the use of oblique positions is required for most examinations performed with a single-plane rapid film-changer or a cine unit. The right anterior oblique position is useful in the demonstration of atrioventricular valves (i.e., mitral stenosis) and in the separation of aorta and pulmonary artery (i.e., tetralogy of Fallot). The left anterior oblique position is preferred in study of the atrial and ventricular septa in presence of intracardiac shunts. Rationale for Use of Tilted Left Anterior Oblique Position In the postero-anterior and true lateral projections of the angiographic image, there is inevitable overlap of the central portions of the atrial and ventricular chambers and the atrioventricular valves. With atrial septal defects, the overlap of the cardiac chambers precludes precise localization of a defect site (2). Correlation of the frontal projection with the lateral is necessary for localization of high ventricular septal defects (1). In the conventional left anterior oblique position, the ventricles lie nearly directly in front of their respective atria. As a result, the interventricular septum is foreshortened and superimposed on the atrial septum. The atrioventricular valves are not visible when the atria are opacified because the contrast medium overlaps the valvular plane.