Coding of coronary arterial origin and branching in congenital heart disease: The modified Leiden Convention

Variations in coronary anatomy are common and may relate to the position of the coronary ostium relative to the aortic sinus, the angle of coronary take-off, or the course of the coronary arterial branches. Several classification systems have been proposed. However, they all lack a simple rationale that is applicable irrespective of the relative position of the great arteries, as well as in bicuspid aortic valves. We present a modification of a relatively simple system introduced in the early 1980s, designated the "Leiden Convention."

The first step of the Leiden Convention is that the clinician takes position in the nonfacing sinus of the aorta looking toward the pulmonary orifice. The right-hand facing sinus is sinus 1, and the left-hand facing sinus is sinus 2. The coronary branches arising from sinus 1 are annotated proceeding in a counterclockwise fashion toward sinus 2. "Usual" (normal) coronary anatomy would be 1R-2LCx. Given their clinical relevance, single sinus coronary arteries are discussed separately.

This system was originally designed and highly applicable in hearts with an altered great artery relationship, such as in the variable and complicated patterns seen in transposition of the great arteries and double outlet right ventricle. The modified system also can be used in cases with normally related great arteries, cases with single sinus coronary arteries, and cases with bicuspid aortic valves.

The modified Leiden Convention is not a strict classification but a simple coronary coding system that is broadly applicable.