Based upon the classic pathologic studies of Kalbfleisch and Hort (American Heart J 1977;94:183), coronary branches within the posterior interventricular groove, or PDA territory, supply about 18% of the total LV mass. This mass includes septal portions of basal, mid and apical inferior segments as well as the adjacent basal and mid inferoseptal and apical septal segments of the 17-segment LV model. (With a progressively larger RCA the RCA contribution can increase to 33% by the inclusion of PL LV free wall branches.) Because of the size and strategic importance of PDA region, CARAT makes a special attempt to capture the considerable variability in blood supply to this region.
The coronary tree assembly stragegy of CARAT is a stepwise selection of coronary branches and sizes from template options presented under the tabs on the right half of the CARAT window. Branches selected from the template tabs are those that follow a ‘usual’ pathway or configuration and have no sub-branches. The secondary branch selection process captures more branch detail when clinically important sub-branching patterns and pathway variants require documentation.
Secondary branch option and variant menus are revealed by ‘right-clicking’ on the branch or segment in need of alteration. An alternate selection is then made by selecting (‘left-clicking’) on the desired option.
Figure 1 – PDA (Type 1, Type 2 and Type 3 LAD) Configurations.
The IV Groove tab in CARAT presents the first step in describing PDA region blood supply (see black outline in Figure 1). The top row of choices reflect the classsic balanced configurations of LAD and PDA (Types I, II and III).
The two IV groove variants shownin the lower two icons represent the following scenarios: left, a Type II LAD is paired with a small PDA; and right, a Type I LAD is paired with a small PDA. In these cases the resulting ‘gap’ in the AV groove is supplied by an anomalous adjacent branch. (These options are shown in Figure 2.)
Figure 2 - IV Groove Distal PDA and Apex ‘Gap’ Scenarios ‘Remote’ supply of distal PDA and Apex.