By Yong-Ming He, MD, PhD, Ming-Xing Xu, MD

Division of Cardiology, The First Affiliated Hospital of Soochow University

E-mail: heyongming@catletscore.com or heyongming@suda.edu.cn

Give me a reference and a ruler, and I can characterize all the variations of coronary anatomy.

Identity and difference make a world.

                                                                  ------By Matthew Yong-Ming He

It is strongly recommended that you should read through the SYNTAX score before you start this
tutorial.(https://www.ncbi.nlm.nih.gov/pubmed/19758907)

The CatLet score in PDF version is available now at http://jtd.amegroups.com/article/view/34094 & https://onlinelibrary.wiley.com/doi/full/10.1002/ccd.28724

Abbreviations

Myocardial blood supply is proportional to myocardial mass

Numerous studies have been performed to determine the actual flow to the left ventricular myocardium (1-8). These data demonstrate that actual myocardial blood is proportional to muscle mass (1,2,4-8). In other words, muscle mass can be utilized to estimate regional flow, and the importance of the blood vessels supplying this portion of myocardium.

Left ventricular segmentation

Because the 17 myocardial segment model is based on the approximately even division of the left ventricle as shown in Figure 1 (9), each segment can be understood either as 1 mass unit or as 1 actual flow unit. The importance of a blood vessel (weighting factor) depends on how many segments the blood vessel supplies rather than on the nomenclature of the blood vessel. The more segments a blood vessel supplies, the more important it is.

 Figure 1. Display, on a circumferential polar plot, of the 17 myocardial segments and the recommended nomenclature for tomographic imaging of the heart. Modified from reference (9).

Proposal of a benchmark type of coronary artery circulation among individuals

Although there is tremendous variability in the coronary artery blood supply to myocardial segments, it is generally considered appropriate to assign individual segments to specific coronary artery territories, which is defined as the benchmark type in this study (10). The assignment of the 17 segments to one of the 3 major coronary arteries is recommended by AHA Scientific Statement as shown in Figure 2 (9).

Figure 2. The 17 myocardial segments assigned to the territories of left anterior descending artery (LAD), right coronary artery (RCA), and left circumflex coronary artery (LCX). Reprinted from reference (9).

Division of the left heart into the three areas according to territories of coronary arteries in the benchmark type

In the benchmark type, the left heart is divided into 3 areas corresponding with the territories of the coronary arteries: the septal area with 6 segments, which are competitively perfused by LADex (LAD excluding diagonals) and PDA (posterior descending artery); the diagonal-obtuse marginal area (DOMA) with 8 segments, which are competitively perfused by diagonals and obtuse marginal arteries; and the inferior wall with 3 segments, which are competitively perfused by posterolateral vessels (PLVs) off RCA or LCX.

Competitive coronary blood supply accounts for tremendous variability in the coronary artery trees among individuals

The RCA and LCA provide competitive patterns of blood supply for the entire left heart and for the above described 3 areas. Specifically, LADex competes with PDA in supplying the septal area; diagonals compete with obtuse marginal branches in supplying the DOMA; and PLVs off RCA compete with PLVs off LCX in supplying the inferior wall. A pair of competitive blood vessels (RCA vs LCA, LADex vs PDA, etc.) conform to the law of growth and decline. That means a large RCA is associated with a small LCA, large diagonals with small obtuse marginal arteries, PLVs off RCA with small PLVs off LCX, long LAD with short PDA, and vice versa.

Reclassification of coronary artery circulation patterns

Reclassification of RCA dominance

The size of the RCA is defined depending on the distribution of the LCX according to the rule of competitive blood supply. Stem LCX usually courses in the atrio-ventricular sulcus and, on the way, gives rise to branches supplying the anterolateral wall, the inferolateral wall, and even the inferior wall in case of large LCX. At one extreme, a large LCX, with a diminutive RCA, provides blood flow to the anterolateral wall, inferolateral wall, the inferior wall and the inferior septum. At the other extreme, the LCX is small with perfusion of only a relatively small portion of the anterolateral wall, and the large RCA provides blood flow to the inferior septum, the inferior wall, the inferolateral wall and the remaining portion of the anterolateral wall.

Identification of the left atrio-ventricular sulcus (LAVS) on the angiograms in the left anterior oblique 40º/cranial 20º view (LAO 40º/cranial 20º view)

The stem LCX (not its branches) usually runs in the left atrio-ventricular sulcus (LAVS). Therefore, the stem LCX’s course on the angiograms can be utilized to indicate the LAVS. The crux cordis approximately falls upon the perpendicular line via the aorta ostium of the LCA (aorta wall) as shown on the angiograms. The crux cordis is the intersection point of the perpendicular line with the LAVS. In the LAO 40º/cranial 20º view, the LAVS runs from the upper right to the lower left, starting at the junction of the first quarter of the leftmost margin of the left heart with an approximately right angle referring to the left heart margin and terminating at the crux cordis.

Figure 3. Identification of the left atrio-ventricular sulcus (LAVS) on the angiograms in the LAO 40º/cranial 20º view. LCA angiography revealed LAD, LCX as well as RCA supply territories via the collateral connections in a RCA CTO patient.

Definitions of RCA sizes

In the LAO 40º/cranial 20º view, the LAVS is evenly divided into 3 parts from its starting point to the crux cordis.

 Figure 4. Reclassification of RCA according to the LCX size in the LAO 40º/cranial 20º view.

PDA zero (left dominance): RCA gives no rise to any branches supplying the left ventricular myocardium. The entire left ventricular myocardium is supplied by the LCA. Figure 4a

PDA only: The stem LCX gives rise to a significant branch from the third part of the LAVS to supply the entire inferior wall in the LAO 40º/cranial 20º view. RCA provides blood flow only to the inferior septum. Figure 4b.

Small RCA: The stem LCX gives rise to a significant branch from the second part of the LAVS to supply a portion of the inferior wall in the LAO 40º/cranial 20º view. RCA provides blood flow to the inferior septum and the remaining portion of the inferior wall. Figure 4c.

Average RCA: The stem LCX gives rise to a significant branch from the first part of the LAVS to supply the inferolateral wall in the LAO 40º/cranial 20º view. RCA provides blood flow to the inferior septum and the entire inferior wall. Figure 4d.

Large RCA: The stem LCX gives no rise to a significant branch from the first part of the LAVS to supply the inferolateral wall, but only gives rise to branches to supply the anterolateral wall in the LAO 40º/cranial 20º view. RCA provides blood flow to the inferior septum, the inferior wall and the inferolateral wall. Figure 4e.

Super RCA: The stem LCX gives rise to small branches to supply a portion of the anterolateral wall in the LAO 40º/cranial 20º view. RCA provides blood flow to the inferior septum, the inferior wall, the inferolateral wall and the remaining portion of the anterolateral wall. Figure 4f.

Reclassification of diagonal size

The diagonal-obtuse marginal area (DOMA) of the left heart

The diagonal-obtuse marginal area (DOMA) of the left heart is competitively perfused by both diagonals (LAD) and obtuse marginal branches (LCX). In the LAO 40º / cranial 20º view, the DOMA takes on the approximate shape of a spindle delineated by discernable anatomical markers on angiographic coronary angiograms. Before giving rise to obtuse marginal arteries, initial stem LCX courses usually transversely in the atrioventricular sulcus and delineates the upper border of the DOMA. LAD almost constantly courses in the anterior interventricular sulcus and delineates the right border of the DOMA. The DOMA’s left and inferior margins are recognizable because of sufficient contrast between the heart margin and its surrounding tissues on angiograms. An imaginary line 1 starting from the apex divides the DOMA into 2 similar portions. Another imaginary line 2 perpendicular to the line 1 at its midpoint also divides the DOMA into 2 portions. Thus, we get 4 quadrants counterclockwise over the DOMA: I, II, III, and IV as shown in Figure 5.

Figure 5. The diagonal-obtuse marginal area (DOMA) delineated by anatomical markers and its four quadrants in diastole on coronary angiograms in the LAO 40º / cranial 20º view (left). Note that the DOMA’s left border is based on the margin of the left heart, rather than on the obtuse marginal branches, where tremendous variability has been frequently observed in terms of their origins and their running over the DOMA. Two imaginary lines divide the DOMA into 4 quadrants on the schematic diagram (right).

Definitions of diagonal (Dx) sizes

Small Dx: Dx distributing over ≤2 quadrants is defined as small and supplies less than 1/2 of the entire anterior wall with approximately 1.5 or less segments (Figure 6a).

Inter. Dx: Dx distributing over 3~4 quadrants is defined as intermediate and supplies more than 1/2 of the entire anterior wall with approximately 1.5~3 segments (Figure 6b).

Large Dx: Dx distributing over > 4 quadrants is defined as large and supplies the entire anterior wall as well as a portion of the anterolateral wall in excess of 3 segments (Figure 6c).

Figure 6. Reclassification of diagonal size according to its distribution over the four quadrants: Figures 6a  indicated small diagonals; Figures 6b, intermediate diagonals; and Figure 6c, large diagonals.

Reclassification of LAD length

Short LAD: LAD terminates before the apex and supplies the whole anterior septum with approximately 3 segments (Figure 7a);

Average LAD: LAD reaches the apex and supplies the whole anterior septum and the apex with approximately 4 segments with a terminal shape of inverted Y’ (Figure 7b);

Long LAD: LAD turns around the apex notch and runs further in the posterior interventricular sulcus, supplying the whole anterior septum, apex and a portion of posterior septum with approximately 5 segments (Figure 7c).

Figure 7. Different LAD lengths superimposed on the left heart surface in the vertical long axis view of the left heart at the level of anterior interventricular sulcus.

Reclassification by subdividing into 54 coronary circulation patterns

Six types of RCA dominance, 3 types of diagonal size, and 3 types of LAD length together result in a total of 54 patterns of coronary artery circulation, which are used to account for the tremendous variability in coronary anatomy among individuals.

Modified definitions of the coronary artery tree segments

The definition of the coronary artery tree segments is based on the classification proposed by the AHA (11) and on the modification for the ARTS I and II trials (12). We have further modified this arterial segmentation system to adapt to our angiographic scoring system. We have adopted most nomenclatures of coronary artery tree segments in the SYNTAX score (13). In our angiographic scoring system, definitions for segments 16 series, 7 series, 9 series, 12 series, 14 series, and segments 11, 13 and 15 have been modified as shown in Figure 8.

Figure 8. Fully-fledged 3 major epicardial coronary arteries of RCA, LAD and LCX. Segments 16 series, 7 series, 9 series, 12 series, 14 series, and segments 11, 13 and 15 have been modified.

Seg 1. Right coronary artery (RCA) proximal: adopted as in the SYNTAX score;

Seg 2. RCA mid: adopted as in the SYNTAX score;

Seg 3. RCA distal: adopted as in the SYNTAX score;

Seg 4. Posterior descending artery (PDA) adopted as in the SYNTAX score;

Seg 16. Main posterolateral vessels (PLVs) from RCA: adopted as in the SYNTAX score.

Seg 16a. First PLV of the same size from segment 16.

Seg 16b. Second PLV of the same size from segment 16.

Seg 16X. Major PLV from segment 16 regardless of its origin.

Seg 16S. Minor PLV from segment 16 regardless of its origin with a preset segment difference of 0.5 compared with major PLV.

Seg 16&. Only large PLV from segment 16.

Seg 16c. Obtuse marginal from segment 16, supplying a portion of inferolateral or even anterolateral wall.

Seg 5. Left main (LM) adopted as in the SYNTAX.

Seg 6. Proximal left anterior descending artery (LAD): First third of LAD from its origin to the apex, usually ending at the first major septal branch.

Seg 7 series. Middle LAD: Second third of LAD from its origin to the apex.

Seg 8. Distal LAD: Remaining third of LAD from its origin to the apex, usually wrapping around the apex.

Seg 9a. First diagonal (Dx) of the same size from Seg 6 or 7.

Seg 9b. Second Dx of the same size from Seg 6 or 7.

Seg 9X. Major Dx from Seg 6 or 7 regardless of its origin.

Seg 9S. Minor Dx from Seg 6 or 7 regardless of its origin, with a preset segment difference of 0.5 compared with Seg 9X.

Seg 9&. Only large Dx usually from Seg 6.

Seg 7&. Mid LAD giving rise to an only large Dx

Seg 7X. Mid LAD giving rise to a major Dx.

Seg 7S. Mid LAD giving rise to a minor Dx.

Seg 7E. Mid LAD giving rise to a Dx of the same size.

Seg 7. Mid LAD giving no rise to any Dx. The only large Dx usually arises from segment 6.

Seg 11. Proximal left circumflex (LCX): adopted as in the SYNTAX score.

Seg 12a. First obtuse marginal (OM) of the same size from LCX running over the general area of the obtuse margin of the heart.

Seg 12b. Second OM of the same size from LCX running in the same direction as Seg 12a.

Seg 12X. Major OM from LCX running over the general area of the obtuse margin of the heart regardless of its origin.

Seg 12S. Minor OM from LCX running in the same direction as 12X regardless of its origin, with a preset segment difference 0.5 compared with Seg 12X.

Seg 12&. Only large OM from LCX running over the general area of the obtuse margin of the heart.

Seg 13. Distal LCX: adopted as in the SYNTAX score.

Seg 14b: Second PLV of the same size from Seg 13.

Seg 14X: Major PLV from Seg 13 regardless of its origin.

Seg 14S: Minor PLV from Seg 13 regardless of its origin, with a preset segment difference of 0.5 compared with Seg 14S.

Seg 14&: The only large PLV from Seg 13 regardless of its origin.

Seg 15: PDA from LCA adopted as in the SYNTAX score.

Up to “2 blood vessels” sufficiently cover all the variations of branches arising from a main branch

We set the LAD and its diagonals as an example. If the LAD gives rise to 2 diagonals, these 2 diagonals only have two possibilities: the same or different sizes. If the LAD gives rise to 3 diagonals, we still think of them as “2 diagonals” by way of combining two out of the three diagonals into one. The “2 diagonals” with the same size will be named Seg 9a and 9b, respectively; the “2 diagonals” with different sizes will be named Seg 9X and 9S, respectively, according to their sizes. Branches arising from LCX or RCA have been approached in the same way.

Law of flow conservation (14)

According to the law of flow conservation, a parent vessel equals the sum of its daughter vessels in terms of blood flow, thus, Q=Q1+Q2. (Figure 9). Weighting factor assignment strictly follows this law, therefore, a parent vessel always equals the sum of its daughter vessels in terms of weighting factors.

Figure 9. Law of flow conservation: a parent vessel equals the sum of daughter vessels in terms of blood flow. Arrow indicates blood flow direction.

Weighting factors assigned to LAD, LCX and RCA in the benchmark type.

According to the 17 myocardial segmentation model in the benchmark type (9), the LAD supplies 7 segments: 1, 2, 7, 8, 13, 14, and 17; the LCX supplies 5 segments: 5, 6, 11, 12, and 16; and the RCA supplies 5 segments: 3, 4, 9, 10, and 15. Correspondingly, weighting factors are 7.0 for LAD, 5.0 for LCX, and 5.0 for RCA in this benchmark type (9). Specifically, LAD divides into LADex (excluding diagonals) and diagonals, supplying 4 segments and 3 segments, respectively; RCA divides into PDA and PLVs, supplying 2 segments and 3 segments, respectively. Correspondingly, weighting factors are 3.0 for diagonals, 2.0 for PDA, and 3.0 for PLVs, respectively, in this benchmark type. See table 2.

 Table 2. Weighting factors assigned to coronary artery tree segments in the benchmark type. 

Notes: Values in the golden cells are according to the assignment of the 17 myocardial segments to one of the 3 major epicardial coronary arteries recommended by AHA Scientific Statement in the benchmark pattern of coronary circulation. Values assigned in the green cells strictly obey the matrix operations elaborated below immediately. Values assigned in the yellow cells are fractions of those marked with &’, among which values marked with X’ or S’ with a difference of 0.5. RCA indicates right coronary artery; LAD, left anterior descending; LCX, left circumflex; Dx, diagonals; Comb. Dx, all the diagonals arising from LAD; PDA, posterior descending artery; and Comb. PLVs, all the posterolateral vessels arising from LCX or RCA. NULL indicates unavailability of blood vessels in this type of coronary artery circulation.

Segment weighting factor relationships in the benchmark type as shown in the table 2

According to the law of flow conservation, we can derive the following equations:

LM equals the sum of LAD and LCX in terms of blood flow, which is briefly expressed as Seg 5=Seg 6+Seg 11

Seg 5=Seg 6+Seg 11;

For RCA,

Seg 16=Seg 16&+Seg 16c;

Seg 16&=Seg 16X+Seg 16S = Seg 16a+Seg 16b=2Seg 16a=2Seg 16b;

Seg 1=Seg 2=Seg 3=Seg 4+ Seg 16;

For LCX,

Seg 12&=Seg 12X+Seg 12S=Seg 12a+Seg 12b=2Seg 12a=2Seg 12b;

Seg 13&=Seg 11-seg 12&;

Seg 13&=Seg 14X+Seg 14S= Seg 14a+Seg 14b=2Seg 14a=2Seg 14b

For LAD,

Seg 9&=Seg 9X+Seg 9S=Seg 9a+Seg 9b=2Seg 9a or 2Seg 9b

4.0=Seg 6-Seg 9&

6.0=Seg 6-Seg 9&+Seg 15

Seg 8=2.0;

Seg 7=Seg 8+1.0;

Seg 7E=Seg 8+Seg 9a or 9b+ 1.0;

Seg 7X=Seg 8+Seg 9X+ 1.0;

Seg 7S=Seg 8+Seg 9S+ 1.0; and

Seg 7&=Seg 8+Seg 9&+1.0.

For PDA zero,

Seg 15=6-(Seg 6-Seg 9&);

For PDA only to Super RCA dominant,

Seg 4=6-(Seg 6-Seg 9&).

These segment weighting factor relationships revealed above in the benchmark type are also applicable to those in non-benchmark types of coronary artery circulations.

Weighting factors based on observed RCA, LCX and LAD anatomy

Based on the standard 17 segment model of the LV, the weighting factors are derived from the above-described anatomic details of RCA, LAD, LCX or their branches (variations in coronary anatomy). The benchmark pattern of coronary circulation is used as reference and weighting factors with discrete values are added to account for the variations in circulation pattern. Use of preset, discrete incremental values is a compromise between the convenience of clinical use and the variability in coronary artery circulation. A preset incremental value of 1 or 1.5 was used to describe differences in in LAD length, in diagonal branch size or in RCA supply territory as listed in tables 3, 4 and 5.

Table 3. Progressive LAD weighting factor changes (with a step size of 1.0) across LAD lengths with both the same RCA dominance (for example, average) and the same diagonal size (for example, small).

Notes: Abbreviations as listed in table 2.

Table 4. Progressive diagonal weighting factor changes (with a step size of 1.5) across diagonal sizes with both the same LAD length (for example, short) and the same RCA dominance (for example, small).

Notes: Abbreviations as listed in table 2.

Table 5. Progressive RCA weighting factor changes (with a step size of 1.5) across RCA dominances with both the same diagonal size (for example, intermediate) and the same LAD length (for example, average).

Notes: Abbreviations as listed in table 2.

Weighting factor assignment for coronary artery tree segments in different RCA dominances with different LAD lengths or diagonal sizes

Weighting factors for coronary artery tree segments in the benchmark type are shown as reference, and a preset segment number difference of 1.0 or 1.5 is highlighted in golden. This approach allows to derive the weighting factors for all the coronary artery tree segments in the 54 types of coronary artery circulation proposed in this angiographic scoring system (table 6).

--Weighting factor derivation for PDA and PLVs

The septal wall (anterior and inferior) with 6 segments according to the benchmark type is perfused competitively by LADex and PDA. Therefore, their weighting factor sum is always 6.0 regardless of LAD lengths. Understandably, weighting factor for segment 4 (PDA) is 3.0, 2.0 and 1.0, respectively, corresponding to short, average and long LAD length, respectively.

The inferior wall with 3 segments according to the benchmark type is perfused competitively by PLVs arising from RCA or LCX. Therefore, their weighting factor sum is always 3.0 regardless of RCA dominances. Understandably, weighting factor for segment 14& is constantly 3.0 in PDA zero or PDA only; the weighting factor for segment 16& is constantly 3.0 in average, large or super RCA dominant; and the weighting factor sum of segments 14& and 16& is constantly 3.0 in Small RCA dominant. Segment 16c represents obtuse marginal arteries arising from segment 16 and its weighting factor is 1.5 and 3.0 in large and super RCA dominant, respectively. Thus, the weighting factors for segment 1, 2 or 3 equal the weighting factor sum of segments 4 and 16 in the corresponding cells. The weighting factors for segment 16 equals the weighting factor sum of segments 16& and 16c in the corresponding cells.

--Weighting factor derivation for Dx and LAD

Referring to the benchmark type, weighting factors for Dx (segment 9&) are 2.0, 3.0 and 4.0, respectively, according to different sizes of Dx. Weighting factors for LAD segments depend both on the segment numbers they supply and on the diagonals arising as shown in Figure 10.

Figure 10. Weighting factor derivation for LAD segments. Suppose an average LAD length with a Dx take-off. Segment 8 of LAD provides blood supply to the apical anterior septum and apex segment with 2 segments; thus, the weighting factor for segment 8 is 2.0. Segment 7 provides blood supply to the mid anterior septum, apical anterior septum and apex segment with 3 segments; thus, the weighting factor for segment 7 is 3.0. Likewise, the weighting factor for segment 6 is 4.0 in the absence of a Dx. As a matter of fact, segment 6 gives rise to a Dx; therefore, its weighting factor should incorporate the contribution by the Dx. Suppose the weighting factor for the Dx is 1.5 and the weighting factor for segment 6 should therefore be 5.5.

--Weighting factor derivation for LCX and obtuse marginal arteries

The weighting factors for the LCX are indirectly derived from the weighting factor differences between LM and LAD in the corresponding cells, briefly expressed as LCX=LM-LAD or Seg 11=Seg 5–Seg 6). The weighting factors for segment 12& are indirectly derived from the weighting factor differences between segments 11 and 13 in the corresponding cells (Seg 12&=Seg 11-Seg 13).

Table 6. Weighting factors assigned to coronary artery tree segments in different RCA dominances with different sizes of diagonals or lengths of LAD.



Notes: the benchmark pattern of coronary circulation is used as reference and weighting factors with discrete values in the golden cells are added to account for the variations in circulation pattern. Values assigned in the green cells strictly obey the matrix operations. Values assigned in the yellow cells are fractions of those marked with &’, among which values marked with X’ or S’ with a difference of 0.5.  RCA=right coronary artery; LAD=left anterior descending; LCX=left circumflex; OM=obtuse marginal; Dx=diagonals; Comb. Dx=all the diagonals arising from LAD; PDA=posterior descending artery; and Comb. PLVs=all the posterolateral vessels arising from LCX or RCA.

Lesion scoring and the need for adapting modfications

The degree of stenosis is also considered in deriving the lesion scoring. If the blood vessel is totally occluded, the coronary artery segment weighting value is multiplied by 5.0. If the blood vessel is more than 50-99% diameter stenosis, the value is multiplied by 2.0. The lesion score is a product of the weighting factor of a blood vessel and its stenosis degree. The coronary artery lesion scores will then be added to derive the total score(15). A score of zero indicates no stenosis of coronary artery tree, and the higher the score, the greater the stenosis is. Within one segment, direct scoring will overestimate the severity of coronary artery disease in the presence of significant side branches (SB, >1.5 mm in diameter) preceding the main branch (MB) lesion regardless of their normal or diseased status. Thus, lesion scoring should be modified as shown in Figure 11.

Figure 11. Lesion scoring modification within one segment in the presence of a significant branch (SB). Arrow=blood flow direction; PMB=proximal main branches; DMB=distal main branches; SB=side branch; dashed gray lines=occluded segment distal to the occlusive lesion. We often encounter a coronary artery segment with a take-off of a significant side branch (SB). Suppose the weighting factor is 7.0 for this segment and 3.0 for the SB. The main branch (MB) of the segment divides into proximal or distal MB referring to the SB. According to the law of flow conservation, the weighting factor for the distal MB is 4.0 (Left). Within one segment, an occlusive lesion for this segment distal to the SB (DMB lesion) is scored as 7.0×5=35.0 according to the CatLet scoring algorithm (Right). Actually, the DMB lesion’s weighting factor is only 4.0 because of the presence of the SB. Hence, the CatLet scoring algorithm overestimates the severity of the occlusive DMB lesion. The scoring values for this segment should be modified for 7.0×5-3.0×5=20.0 using formula 1.

The scoring modification is required in the following 6 scenarios according to corresponding formulas.

Occluded lesions

In case of an occluded MB lesion preceded by an intact significant SB in a segment (1 lesion) (Figure 12a), the final score for the lesion should be modified via Formula 1 as the weighting factor of the MB has covered the intact SBs’, which is actually not adversely affected.

S=subtotal score -W SBs×5;                                   (1)

In case of an occluded MB lesion preceded by an involved significant SB in a segment (within 1 lesion) (Figure 12b), the final score for the lesion is modified via Formula 2 as the MB and the SB will be scored simultaneously as one lesion. As a matter of fact, the weighting factor of the MB has already covered the SB’s.

 S=subtotal score-W SBs×8                                 (2)

In case of an occluded MB lesion preceded by a separate lesion on SBs (2 separate lesions, one is on the MB and the other is on the SB) in a segment (Figure 12c), final score for the MB lesion is modified via Formula 3 as the weighting factor of the MB lesion covered the diseased SBs’, which should be subtracted from that of the MB. The lesion on the SB will be scored separately.

S = subtotal score-W SBs×5;                          (3)

Non-occluded lesions

In case of a non-occluded MB lesion preceded by intact SBs in a segment (1 lesion) (Figure 12d), the final score for the MB lesion is modified via Formula 4 as the weighting factor of the MB lesion has covered the intact SBs’, which is actually not adversely affected.

S =subtotal score-W SBs×2;                               (4)

In case of a non-occluded MB lesion preceded by an involved significant SB in a segment (within 1 lesion) (Figure 12e), the final score for the lesion is modified via formula 5 as the MB and the SBs will be scored simultaneously as one lesion, in which the weighting factor of the MB has already covered the SBs’.

S=subtotal score-W SBs×2;                              (5)

In case of a non-occluded MB lesion preceded by a separate lesion on SBs (2 separate lesions) in a segment (Figure 12f), the final score for the MB lesion is modified via Formula 6 as the weighting factor of the MB lesion has already covered the SBs’, which should be subtracted from the MB’s. The lesion on the SBs will be scored separately.

S= subtotal score - W SBs×2;                              (6)

Where S is the modified score for a lesion;

W is the weighting factor of side branches;

Subtotal score is calculated for the lesion according to the CatLet scoring algorithm.

Figure 12. Lesion scoring modification within one segment in the 6 circumstances. The upper row is for the occluded lesion and the lower row is for the non-occluded lesion. PMB or DMB indicates proximal or distal major branches and SB indicates side branches. Dashed gray lines indicate occluded blood vessels distal to the occluded lesion. Figures a & d indicated 1 lesion involving the DMB; Figures b & e indicate 1 lesion involving both the DMB and the SB; and Figures c & f indicate 2 separate lesions involving the DMB and the SB.

Software-based CatLet score algorithm

The CatLet score calculation is feasible by use of a computer program consisting of sequential and interactive self-guided questions (available at http://www.catletscore.com).

The algorithm includes 15 main questions. The first question includes 3 sub questions: RCA dominance, Dx size and LAD length. Answering these 3 sub-questions will define one of 54 types of coronary artery circulations proposed in this angiographic scoring system (different from the SYNTAX score) (13). The second question includes two options: option 1 is for recording normal coronary artery anatomy; and option 2 (most important) is for evaluating the lesions. Question 3 addresses lesion-based unlimited segment selection. Question 4 addresses 2 native or in-stent lesion types, including non-occlusions and acute total occlusion (ATO).

For non-occlusion or ATO lesions, questions 5-12 address the lesion-based evaluation, including involved segments, calcifications, angulations, and thrombus, which are most similar to those adopted in the SYNTAX score (13), but differ in only qualitatively recording these adverse characteristics as “Yes” or “No” in our scoring system (table 7). Question 12 addresses scoring modification if necessary. Upon completion of question 12, the algorithm proceeds to the last question or to another cycle of “add another lesion”. The last question of the CatLet score algorithm, diffuse disease/small vessels, similar to those in the SYNTAX score, is also only qualitatively recorded (table 7). For a patient with coronary artery disease, it takes around 5-10 minutes to process a patients depending on the complexity and severity of coronary artery disease.

Table 7. Scoring and describing of lesion’s adverse characteristics.

In the CatLet score, only the lesion's stenosis was scored, and the lesion's remaining adverse characteristics were instead qualitatively recorded. CTO is defined an occluded coronary segment with TIMI flow 0 for ≥3 months duration. Definitions for lesions' adverse characteristics are the same as listed in the Syntax score (13). In-stent lesions are defined as angiographic diameter stenosis >50% at the stent segment or its adjacent edges within 5 mm (15).

Scoring of a sample patient according to the CatLet angiographic scoring system

As shown in Figure 16, coronary circulation pattern was first evaluated overall according to LAD length, Dx size and RCA size (Figure 16A-C) before the non-occlusive lesion on proximal LAD (segment 6) was scored. Average RCA was judged according to the presence of a significant branch arising from LCX. The lesion was amplified right upper in the Figure 16C. Adverse non-stenotic characteristics pertinent to the lesion were no longer scored and qualitatively recorded as Yes or No. Detailed information on the lesion was displayed in Figure 16D.

Figure 16. Scoring of a sample patient according to the CatLet score algorithm. 

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