Angiographic Factors

The American College of Cardiology/American Heart Association (ACC/AHA) created a scoring system that classified lesions according to their complexity, likelihood of successful dilation, and the likelihood of an adverse event. Lesions were classified as either type A, B, or C, with C the highest risk lesions, based on lesion characteristics (Tables 12-1 and 12-2).

^{Table 12-1} The ACC/AHA Lesion Classification Scheme

^{Table 12-2} Lesion Characteristics and the Increased Risk of Ischemic Complications (Based on Multivariate Analysis)

The ACC/AHA Lesion Classification Scheme has since been modified in that lesions with one “type B” characteristic are designated as “type B1” while lesions with two or more “type B” characteristics are designated as “type B2” lesions. Since this classification was first implemented in 1988, significant advances in PCI techniques have allowed treatment of more complex lesions with lower risks. In the current era of coronary stenting, it is primarily the type C lesions that are associated with lower success and higher complication rates.

In the mid-1990s, an era in which coronary stents and platelet glycoprotein IIb/IIIa inhibitors were frequently utilized, Ellis and coworkers analyzed a large database of patients undergoing PCI. Ten angiographic factors were identified that correlated with greater risk of complication. The two factors associated with the greatest increased risk were degenerated saphenous vein grafts (relative risk 4.18) and nonchronic total occlusion (relative risk 4.74). Other factors included long lesions, lesions with large filling defects, calcified angulated lesions, eccentric lesions, and old saphenous vein grafts (Table 12-2). The finding of marked increased risk in degenerated vein grafts supports the practice of using distal protection devices during PCI of such lesions.

Angiographic Risk Assessment Using the SYNTAX Score

The SYNTAX score, an angiographic grading tool to determine the complexity of coronary artery disease (CAD), was derived from pre-existing risk assessment classifications from numerous studies and expert consensus. The SYNTAX score is the sum of the points assigned to each individual lesion identified in the coronary tree with >50% diameter narrowing in vessels >1.5 mm diameter. The coronary tree is divided into 16 segments according to the AHA classification (see Fig. 12-1). Each segment is given a score of 1 or 2 based on the presence of disease, and this score is then weighted based on a chart, with values ranging from 3.5 for the proximal left anterior descending artery (LAD) to 5.0 for left main, and 0.5 for smaller branches. The branches <1.5 mm in diameter, despite having severe lesions, are not included in the SYNTAX score. The percent diameter stenosis is not a consideration in the SYNTAX score, only the presence of a stenosis from 50% to 99% diameter, <50% diameter narrowing, or total occlusion. A multiplication factor of 2 is used for non-occlusive lesions and 5 is used for occlusive lesions, reflecting the difficulty of PCI. Further characterization of the lesions adds points. (Fig. 12-1 shows the diagram of vessel segments used in the SYNTAX score.)

Figure 12-1 Definition of the coronary tree segments from the SYNTAX study

1. RCA (right coronary artery) 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.

5. Left main: from the ostium of the LCA (left coronary artery) through bifurcation into left anterior descending and left circumflex branches.

6. LAD (left anterior descending) 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 [right anterior oblique] 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 (left circumflex). 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 14a 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.

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.

(From Sianos G, Morel MA, Kappetein AP, et al. The SYNTAX Score: an angiographic tool grading the complexity of coronary artery disease. EuroIntervention 2005;1:219–227.)

The SYNTAX score algorithm then sums each of these features for a total SYNTAX score. Table 12-3 summarizes the SYNTAX grade categories. A computer algorithm (available online at www.syntaxscore.com) is then queried, and a summed value is produced. Figure 12-2 shows two patients each with three-vessel CAD but very different PCI risk based on SYNTAX scores.

^{Table 12-3} The SYNTAX Score Algorithm

Figure 12-2 Angiographic examples of SYNTAX scores in patients undergoing PCI. Selected angiograms.

(Reprinted from Sianos G, Morel MA, Kappetein AP, et al. The SYNTAX score: an angiographic tool grading the complexity of CAD. EuroIntervention 2005;1:219–227 with permission.)

In patients with SYNTAX score <33, equal outcomes after revascularization were obtained with regard to major adverse cardiac events for both PCI and CABG. For higher SYNTAX scores, CABG had fewer adverse events than PCI. The conclusion of the SYNTAX study showed that the overall safety outcomes (death, cerebrovascular accident, MI) were similar in CABG and PCI patients at 12 months (7.7 vs. 7.6%). There was a higher rate of revascularization in the PCI group (13.7 vs. 5.9%), balanced by a higher rate of cerebrovascular accident in the CABG group (2.2 vs. 0.6%). Of note, the overall PCI major adverse cardiac and cerebrovascular event rate (MACCE) was higher (17.8 vs.12.1%) primarily due to an excess need for repeat revascularization. If one accepts a repeat revascularization as part of the natural history of PCI and not an adverse event, then the difference between revascularization strategies becomes even less (Fig. 12-3).

Figure 12-3 Outcomes of SYNTAX study by SYNTAX scores. Rates of major adverse cardiac or cerebrovascular events among the study patients, according to treatment group and SYNTAX score category. Kaplan-Meier curves are shown for the percutaneous coronary intervention (PCI) group and the coronary artery bypass grafting (CABG) group for major adverse cardiac or cerebrovascular events at 12 months. The 12-month event rates were similar between the two treatment groups for patients with low SYNTAX scores (0–22) (A) or intermediate SYNTAX scores (23–32) (B). Among patients with high SYNTAX scores (=33, indicating the most complex disease), those in the PCI group had a significantly higher event rate at 12 months than those in the CABG group. SYNTAX scores were calculated at the core laboratory. The I bars indicate 1.5 SE. P values were calculated with the use of the chi-square test.

(Reprinted from Serruys PW, Morice, MC, Kappetein AP, et al. Percutaneous coronary intervention versus coronary-artery bypass grafting for severe coronary artery disease. N Engl J Med 2009;360(10):961–972.)

Based on angiographic assessment and the operators’ experience in the cath lab, the number and type of complex anatomic lesions determines which revascularization approach might be selected. However, the physiology of coronary lesions and stenting are strongly related to outcomes. A recent publication by Tonino et al. from the FAME study group reported on what truly constituted three-vessel and two-vessel CAD, making clear that one cannot equate angiographic three-vessel CAD with physiologic three-vessel CAD. Fractional flow reserve thus has important implications for the decision-making process in patients with multivessel disease.

Patient-Related Factors

Several clinical factors can be utilized to identify high-risk PCI, such as the presence of multivessel disease, angioplasty to more than one lesion, suboptimal activated clotting time (ACT), residual stenosis above 30%, depressed ejection fraction, old age (>65 years), unstable angina and recent MI (Table 12-4). A retrospective study from the Mayo Clinic, examining the risk of PCI with the use of glycoprotein IIb/IIIa inhibitors and coronary stents, found that clinical factors such as left main or multivessel disease, an ejection fraction below 35%, or a recent MI were more important than angiographic factors for predicting complications. Other studies have identified the presence of diabetes mellitus and renal disease as indicators of high-risk patients (Table 12-5).

^{Table 12-4} Patient and Clinical Factors Associated With Higher Risk PCI

^{Table 12-5} Elective PCI Patient and Lesion High-Risk Characteristics

Specific High-Risk Subsets