Definitions of the angle between the LMCA ostium and the NCC-RCC commissure. ‘Dot A' was at the NCC-RCC commissure. ‘Dot O' was at the center of the cusp plane of the aortic valve. ‘Dot B' was at the opposite side of dot A on the cusp plane. ‘Dot C' was at the center of the LMCA ostium. The angle between the LMCA ostium and NCC-RCC commissure was ∠BOC. The LMCA ostium was considered to be facing the NCC-RCC commissure when ∠BOC was equal to 0°.