Transposition Of The Great Arteries (TGA)

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Here’s a transesophageal echo (TEE) clip I’ve taken of an interesting congenital condition: transposition of the great arteries (TGA). Whereas the aorta (Ao) normally comes off the left ventricle (LV), in this case, it comes off a very hypertrophied right ventricle (RV).

TGA comes in two variants. D-TGA has atrioventricular concordance but ventriculoarterial discordance resulting in two PARALLEL circulations requiring mixing (ie, via a VSD). Blood flows from SVC/IVC → RA → RV → aorta and the pulmonary veins → LA → LV → pulmonary artery.. Because of this, the RV (normally a thin walled, volume chamber) has to pump the systemic cardiac output to the rest of the body. Over time, this results in significant, pathologic right ventricular hypertrophy (RVH). Historically, D-TGA was repaired using an atrial switch operation (ie, the Mustard procedure), but these days, arterial switch operations are performed.

L-TGA results from double-discordance and ventricular inversion. In other words, the ventricles are flipped. Blood moves in series from the SVC/IVC → RA → LV → PA → lungs → pulmonary veins → LA → RV → aorta. Notice how even though the ventricles are switched, deoxygenated blood and oxygenated blood are where they should be. This is why L-TGA is termed “congenitally corrected.” 90% of these patients also have other lesions such as VSDs, outflow obstructions, complete heart block, and valvular pathology.

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