Clinical research

The SYNTAX Score: an angiographic tool grading the complexity of coronary artery disease
Georgios Sianos1, MD, PhD; Marie-Angèle Morel2, BSc; Arie Pieter Kappetein3, MD, PhD;
Marie-Claude Morice4, MD; Antonio Colombo5, MD; Keith Dawkins6, MD; Marcel van den Brand7, MD, PhD;
Nic Van Dyck8, RN; Mary E Russell9, MD; Friedrich W. Mohr10, MD; Patrick W Serruys1* MD, PhD
1. Department of Interventional Cardiology, Erasmus Medical Center, Thoraxcenter Rotterdam, The Netherlands
2. Cardialysis BV, Rotterdam, The Netherlands
3. Department of Cardiothoracic Surgery, Erasmus Medical Center, Thoraxcenter, Rotterdam, The Netherlands
4. Institut Cardiovasculaire Paris Sud, Massy, France
5. San Raffaele Hospital, Milano, Italy
6. Southampton General Hospital, Southampton, UK
7. Ouderkerk aan den ijssel, The Netherlands
8. Boston Scientific Corporation, Maastricht, The Netherlands
9. Boston Scientific Corporation, Natick Massachusetts, USA
10. Herzzentrum, Leipzig, Germany

Introduction
Optimal revascularization strategy in patients with coronary artery disease remains a subject of debate between interventional cardiologists and surgeons. Numerous large scale randomized trials addressed this issue comparing coronary artery bypass grafting
(CABG) with percutaneous coronary intervention (PCI) in patients with multivessel disease (MVD). Initially these trials compared multivessel balloon angioplasty with CABG1-6 and in a later period multivessel stenting with CABG7-11. These studies clearly demonstrated that there was no difference between the two therapeutic modalities regarding mortality and non fatal myocardial infarction but patients treated with balloon angioplasty or stenting required more often repeat revascularization procedures related to restenosis12,13.
Clearly stenting reduced the gap in the event free survival rate between the two revascularization strategies from 32% in CABRI trial (91% versus 59% in favour of CABG) to 14% in ARTS I trial
(89% versus 75%) but still surgery remained the gold standard for patients with MVD with an event free survival rate around 90%14.
Recently the drug eluting stents were introduced and proven to be very effective in reducing restenosis and the incidence of repeat revascularisation15-18. In the recently conducted ARTS II trial the sirolimus eluting stents were compared with historical CABG data from the ARTS I trial in patients with MVD. The incidence of major

adverse cardiac events was comparable in both approaches, even though the number of vessels and lesions treated were higher than in the previous trials19. However, it has been argued that despite the fact that patients with two or three vessel disease have been included in the aforementioned trials, in the "real world" both interventional cardiologists and surgeons are often confronted with more complex anatomy. Numerous exclusion criteria and disagreement between the surgeons and the interventional cardiologists allowed only 2%-12% of the patients screened to be randomized13.
Another characteristic of these trials was the heterogeneity in the complexity of coronary artery disease of the patients enrolled13. For example, a patient with distal a left-main stem trifurcation lesion in combination with an occluded right coronary artery is pooled together with a patient with three focal lesions in the mid portions of the three coronary arteries. Both are characterised as routinely named “3-vessel disease”, despite the fact that the first patient represents a greater therapeutic challenge for the interventional cardiologist and has completely different prognosis compared to the second patient regardless of the revascularization strategy; percutaneous or surgical. The absence of grading of the severity of coronary artery disease and the lack of comparison of lesion complexity based on pre-treatment angiographic criteria between various groups severely limits the interpretation of the results of these trials.

* Corresponding author: Head of Interventional Cardiology, Ba 583, Thoraxcenter, Erasmus Medical Center, Dr. Molewaterplein 40, 3015 GD,
Rotterdam, The Netherlands
E-mail : p.w.j.c.serruys@erasmusmc.nl
© Europa Edition 2005. All rights reserved.

EuroInterv.2005;1:219-227

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The SYNTAX Score: an angiographic tool grading the complexity of coronary artery disease

Thus, for the selection of the optimal revascularization strategy for patients with three vessel and/or left main stem disease there are three major requirements:
1. The conductance of an “all comer” (no exclusion criteria) study in such patients.
2. Consensus between the interventional cardiologist and the cardiothoracic surgeon for the treatment plan.
3. The quantification of the complexity of coronary artery disease, taking into account not only the number of significant lesions and their location, but also the complexity of each lesion independently.
The SYNTAX (SYNergy between PCI with TAXUS™ and Cardiac
Surgery) study was organized as an all comer study for patients with significant lesions in the left main stem and/or the three epicardial coronary arteries. It will be comprised of a randomized arm and two registries for patients that are not suitable for one of the two revascularization strategies. Patients who have a preference for one of the treatment strategies or patients in whom medical treatment is suggested they will be included in the screening log.
The SYNTAX score has been developed for this study to prospectively characterise the coronary vasculature with respect to the number of lesions and their functional impact, location, and complexity. Higher SYNTAX scores, indicative of more complex disease are hypothesized to represent a bigger therapeutic challenge and to have potentially worse prognosis.

5 times, the LAD approximately 3,5 times (84/16 x 0.66) and the circumflex 1,5 times as much blood as the RCA to the left ventricle.
In a left dominant system the RCA does not contribute to the blood supply of the ventricle. Thus the LM supplies 100% of the flow to the LV. The RCA contribution of blood flow to the LV is now supplied by the LCX. Hence the LAD provides 58% (weighing factor 3.5) and the LCX 42% (weighing factor 2.5) of the total flow to the LV. Using the same principle of relative blood supply to the LV all coronary segments has been given a weighing factor factor, Table 1.
The contribution of each coronary segment to the blood flow to the
LV is used as a multiplication factor for the calculation of the
Leaman score and as such has been transferred to the SYNTAX score. A lesion is defined as significant when it causes (50% reduction in luminal diameter by visual assessment in vessels (1.5mm. Less severe lesions should not be included in the SYNTAX score. The percent diameter stenosis is not considered in the algorithm. Distinction has been made only between occlusive (100% diameter stenosis) and non occlusive (50-99% diameter stenosis) disease.
A multiplication factor of 2 is used for non-occlusive lesions and 5 for occlusive lesions reflecting the difficulty of the percutaneous treatment, Table 1. Importantly, all other adverse lesion characteristics considered in the SYNTAX score have an additive value, Table 2.

Pre-existing classifications

Table 1. Segment weighing factors

The SYNTAX score has been developed based on the following:
1. The AHA classification of the coronary tree segments modified for the ARTS study
2. The Leaman score
3. The ACC/AHA lesions classification system
4. The total occlusion classification system
5. The Duke and ICPS classification systems for bifurcation lesions
6. Consultation of experts
Each of these classifications has been focusing on specific functional and anatomical parameters of the lesions. Thus, the development of a global classification system that would take into account all the variables was necessary.

Segment No

Definition of the coronary tree segments
The definition of the coronary tree segments is based on the classification proposed by the AHA20 and modified for the ARTS I and II trials21. By this system the arterial tree is divided in 16 segments
(Figure 1) and as such has been adopted in the SYNTAX score.

Right dominance Left dominance

1

RCA proximal

1

0

2

RCA mid

1

0

3

RCA distal

1

0

4

Posterior descending artery

1

n.a.

16

Posterolateral branch from RCA

0.5

n.a.

16a Posterolateral branch from RCA

0.5

n.a.

16b Posterolateral branch from RCA

0.5

n.a.

16c

Posterolateral branch from RCA

0.5

n.a.

5

Left Main

5

6

6

LAD proximal

3.5

3.5

7

LAD mid

2.5

2.5

8

LAD apical

1

1

9

First diagonal

1

1

9a

First diagonala

1

1

10

Second diagonal

0.5

0.5

10a Second diagonala

0.5

0.5

Leaman score22

11

Proximal circumflex artery

1.5

12

Intermediate/ anterolateral artery 1

The 'Leaman score' is based on the severity of luminal diameter narrowing and weighed according to the usual blood flow to the left ventricle in each vessel or vessel segment. In a right dominant system, the right coronary artery (RCA) supplies approximately 16% and the left coronary artery (LCA) 84% of the flow to the left ventricle (LV). This 84% is normally directed for 66% to the left anterior descending artery (LAD), and for 33% into the left circumflex coronary artery (LCX). Thus, the Left Main (LM) supplies approximately

12a Obtuse marginala

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1

b

2.5
1
1

12b Obtuse marginal

1

1

13

Distal circumflex artery

0.5

1.5

14

Left posterolateral

0.5

1

14a Left posterolaterala

0.5

1

b

14b Left posterolateral

0.5

1

15

n.a.

1

Posterior descending

Clinical research

Figure 1. Definition of the coronary tree segments
1. RCA proximal: From the ostium to one half the distance to the acute margin of the heart.
2. RCA mid: From the end of first segment to acute margin of heart.
3. RCA distal: From the acute margin of the heart to the origin of the posterior descending artery.
4. Posterior descending artery: Running in the posterior interventricular groove.
16. Posterolateral branch from RCA: Posterolateral branch originating from the distal coronary artery distal to the crux.
16a. Posterolateral branch from RCA: First posterolateral branch from segment 16.
16b. Posterolateral branch from RCA: Second posterolateral branch from segment 16.
16c. Posterolateral branch from RCA: Third posterolateral branch from segment 16.
5. Left main: From the ostium of the LCA through bifurcation into left anterior descending and left circumflex branches.
6. LAD proximal: Proximal to and including first major septal branch.
7. LAD mid: LAD immediately distal to origin of first septal branch and extending to the point where LAD forms an angle (RAO view). If this angle is not identifiable this segment ends at one half the distance from the first septal to the apex of the heart.
8. LAD apical: Terminal portion of LAD, beginning at the end of previous segment and extending to or beyond the apex.
9. First diagonal: The first diagonal originating from segment 6 or 7.
9a. First diagonal a: Additional first diagonal originating from segment 6 or 7, before segment 8.
10. Second diagonal: Originating from segment 8 or the transition between segment 7 and 8.
10a. Second diagonal a: Additional second diagonal originating from segment 8.
11. Proximal circumflex artery: Main stem of circumflex from its origin of left main and including origin of first obtuse marginal branch.
12. Intermediate/anterolateral artery: Branch from trifurcating left main other than proximal LAD or LCX. It belongs to the circumflex territory.
12a. Obtuse marginal a: First side branch of circumflex running in general to the area of obtuse margin of the heart.
12b. Obtuse marginal b: Second additional branch of circumflex running in the same direction as 12.
13. Distal circumflex artery: The stem of the circumflex distal to the origin of the most distal obtuse marginal branch, and running along the posterior left atrioventricular groove. Caliber may be small or artery absent.
14. Left posterolateral: Running to the posterolateral surface of the left ventricle. May be absent or a division of obtuse marginal branch.
14a. Left posterolateral a: Distal from 14 and running in the same direction.
14b. Left posterolateral b: Distal from 14 and 14 a and running in the same direction.
15. Posterior descending: Most distal part of dominant left circumflex when present. It gives origin to septal branches. When this artery is present, segment 4 is usually absent.

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The SYNTAX Score: an angiographic tool grading the complexity of coronary artery disease

Total occlusion classification system24

Table 2. Lesions adverse characteristic scoring
Diameter reduction*
- Total occlusion
- Significant lesion (50-99%)

x5 x2 Total occlusion (TO)
- Age >3months or unknown
+1
- Blunt stump
+1
- Bridging
+1
- First segment visible beyond TO
+1/ per non-visible segment
- Side branch (SB) - Yes, SB