Modified PLAX view in TGA

Parasternal long axis (PLAX) view is often the first view taken during echocardiography. Usually it visualises the left ventricle, left atrium, right ventricular outflow region and aorta. Here we have a modified parasternal view to trace the great vessel arising from the left ventricle distally. The great vessel can be clearly seen as bifurcating into two branches. This appearance is characteristic of pulmonary artery. When aorta is imaged distally, the aortic arch with arch vessels will be seen (not seen in this case). In this case pulmonary artery is arising from the left ventricle (ventriculoarterial discordance). Aorta was seen arising from the right ventricle in another view in this cyanosed infant. There was a small patent ductus arteriosus and a small atrial septal defect. There was mitral pulmonary continuity without any conus tissue intervening. No significant sub pulmonic gradient was noted. The right panel shows non turbulent flow in the main pulmonary artery (blue). Overall the features were consistent with transposition of great arteries (TGA).

tga
LV: Left ventricle; RV: Right ventricle; LA: Left atrium; PA: Pulmonary artery

In transposition of great arteries, the systemic and pulmonary circulations are parallel, unlike the serial situation in normal individuals. Hence good mixing at some level is needed for survival. The best form of mixing is at the atrial level. Hence the role for balloon atrial septostomy for a cyanotic neonate with TGA. Significant mixing at the ventricular level (ventricular septal defect) or great artery level (patent ductus arteriousus) can also improve the survival. When a large ventricular septal defect (VSD) and sub pulmonic stenosis are present the physiology is similar to that of tetralogy of Fallot, with reduced pulmonary blood flow. In the absence of pulmonary stenosis, large VSD will cause increased pulmonary blood flow, pulmonary hypertenison and infants present with cyanosis and heart failure soon after birth.