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. 2021 Jun;11(3):818–839. doi: 10.21037/cdt-19-693-b

Figure 1.

Figure 1

Spiral septum and semilunar valve embryogenesis. (A) Early in development, the precursors to the cardiac outflow tract (OFT) are the truncus arteriosus and the conus. Combined, these make a hollow tubal structure at one end of primitive cardiac mass. The boundary between the conus and truncus arteriosus is marked by an outer curvature of the OFT (the conotruncal curvature). (B) The conotruncal cushions and intercalated cushions develop within the OFT. These cushions occupy four quadrants of the OFT (shown in cross-section). The conotruncal cushions fuse to septate the OFT, as shown in C. (C) Fusion of the conotruncal cushions forms a spiral septum, the truncal part of which divides the OFT into aorta and pulmonary trunk, whereas the conal part separates the OFT into left and right ventricular. The aortic valve and pulmonic valve develop at the conotruncal junction. (D) The conotruncal (superior and inferior septal) cushions give rise to the right and left leaflets of each of the semilunar valves. In the aorta, these are the right and left coronary leaflets, while in the pulmonary valve, these are the right and left cusps. The right-posterior and the left-anterior intercalated cushions develop respectively into the posterior aortic (non-coronary cusp of the aortic valve) and the anterior pulmonic (anterior cusp of the pulmonic valve) leaflets. AL, anterior leaflet; APIC, anterior pulmonary intercalated cushion; AV, aortic valve; CA, coronary artery; CTC, conotruncal cushion; ICC, intercalated cushion; ISC, inferior septal cushion; LL, left leaflet; LCL, left coronary leaflet; LVOT, left ventricular outflow tract; NCL, non-coronary leaflet; PAIC, posterior aortic intercalated cushion; PV, pulmonary valve; RCL, right coronary leaflet; RL, right leaflet; RVOT, right ventricular outflow tract; SSC, superior septal cushion. Images reproduced with permission from Lin et al. Partitioning the heart: mechanisms of cardiac septation and valve development. Development. 2012 Sep 15;139(18):3277-99 and Martin et al. Embryonic Development of the Bicuspid Aortic Valve [Internet]. Vol. 2, Journal of Cardiovascular Development and Disease. 2015. p. 248-72.