Pathophysiology, clinical manifestations, and diagnosis of D-transposition of the great arteries
- David R Fulton, MD
David R Fulton, MD
- Section Editor — Pediatric Cardiology
- Associate Professor of Pediatrics
- Harvard Medical School
- David A Kane, MD
David A Kane, MD
- Assistant Professor
- Department of Pediatric Cardiology
- University of Massachusetts Medical School
Transposition of the great arteries (TGA) is a ventriculoarterial discordant lesion in which the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. The most common form of TGA is the dextro type (referred to as D-TGA) in which the ventricles are oriented so that the right ventricle is positioned to the right of the left ventricle and the origin of the aorta is anterior and rightward to the origin of the pulmonary artery (figure 1). The anatomical defect of D-TGA leads to cyanotic heart disease as a result of two parallel circulations. The first sends deoxygenated systemic venous blood to the right atrium and back to the systemic circulation via the right ventricle and aorta, and the second sends oxygenated pulmonary venous blood to the left atrium and back to the lungs via the left ventricle and pulmonary artery.
The pathophysiology, clinical features, and diagnosis of D-TGA of the great arteries will be presented here. The management and outcome of D-TGA are discussed separately. (See "Management and outcome of D-transposition of the great arteries".)
The prevalence of transposition of the great arteries (TGA) in the United States is estimated to be 4.7 per 10,000 live births . However, a population-based surveillance study of all live births in five counties in Georgia from 1993 and 2005 reported a lower rate of 2.3 per 10,000 live births . TGA accounts for about 3 percent of all congenital heart disease (CHD) disorders and almost 20 percent of all cyanotic CHD defects .
EMBRYOLOGY AND PATHOGENESIS
The specific developmental aspects that result in ventriculoarterial discordance in D-transposition of the great arteries (D-TGA) are not fully delineated. It is hypothesized that the morphogenesis of D-TGA is due to the abnormal growth and development of the bilateral subarterial conus. In normal cardiac development, the subaortic conus and subpulmonary conus are present in the first month of gestation as the great arteries are positioned superior to the right ventricle. Typically, the subaortic conus is resorbed at approximately 30 to 34 days into gestation, which allows for migration of the aortic valve inferiorly and posteriorly into its normal position above the left ventricle. Subaortic conal resorption also leads to the characteristic fibrous continuity between the mitral and aortic valve within the left ventricle. The pulmonary valve retains its association with the right ventricle due to the persistence of the subpulmonary conus .
In D-TGA, however, the subpulmonary conus is resorbed, which allows for posterior migration of the pulmonary valve and the development of fibrous continuity between the pulmonary and mitral valve. The unabsorbed subaortic conus forces the aortic valve anteriorly where it abnormally engages with the morphologic right ventricle. The range in the size and orientation of the subaortic conus is thought to create much of the variability of the coronary arteries’ origins and course .
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