Relation Between Lesion Characteristics and Risk With
Percutaneous Intervention in the Stent and
Glycoprotein IIb/IIIa Era
An Analysis of Results From 10 907 Lesions and Proposal for New
Classification Scheme
Stephen G. Ellis, MD; Victor Guetta, MD; Dave Miller, MS;
Patrick L. Whitlow, MD; Eric J. Topol, MD
Downloaded from http://circ.ahajournals.org/ by guest on July 28, 2017
Background—The currently used American College of Cardiology/American Heart Association lesion classification
scheme dates from an era when balloon angioplasty was the only percutaneous treatment available and major
complications occurred in '7% of patients. Major advances in treatment options would suggest that this scheme may
be outmoded, but the schemes that have been suggested to update lesion classification have not been widely accepted.
Methods and Results—Four thousand one hundred eighty-one consecutive patients (6676 lesions) formed a training set and
2146 patients (4231 lesions) formed a validation set treated from 1995 to 1997 at a single center used by 3 hospital
groups. Twenty-seven pretreatment candidate variables were analyzed with the use of stepwise proportional logistic
regression, and 9 (nonchronic total occlusion with TIMI flow 0, degenerated vein graft, vein graft age .10 years, lesion
length $10 mm, severe calcium, lesion irregularity, large filling defect, angulated $45 degrees plus calcium, and
eccentricity) were independently correlated (P,0.05) with ranked adverse outcome (death, Q-wave or creatine kinase
$33 normal myocardial infarction, or emergency coronary artery bypass grafting..creatine kinase 2 to 33 myocardial
infarction..possibly related to non–Q-wave myocardial infarction..no complication). A scheme based on these
findings and the old American College of Cardiology/American Heart Association scheme were found to have
c-statistics in the validation set of 0.672 and 0.620 (P50.010 vs old scheme), respectively.
Conclusions—Appreciation of these contemporary risk factors for complications of coronary intervention may assist in
patient selection and in risk adjustment for comparison of outcomes between providers. (Circulation.
1999;100:1971-1976.)
Key Words: angioplasty n stents n platelet aggregation inhibitors n risk factors n angiography
T
he American College of Cardiology/American Heart
Association (ACC/AHA) lesion classification scheme
was proposed in 19861 and modified in 1990.2 It is still
widely used to assess risk of patients and lesions undergoing percutaneous intervention and serves as a risk
adjustment parameter in “scorecarding” individual operators and hospitals. Dramatic changes have occurred in the
approach to percutaneous intervention since that time,
allowing treatment of more complex lesions3–5 and lower
overall risk.6 – 8 It would be reasonable to suspect that the
ACC/AHA scheme would need to be revised, but several
schemes that have been suggested have not been widely
adapted.9 –11
Our purpose was to develop a new predictive model for
adverse outcomes with the use of contemporary data and to
compare its performance in a validation sample against that
of the current modified ACC/AHA scheme.2
Methods
Patients
Data from 6327 consecutively treated patients undergoing coronary
intervention from January 1, 1995, until December 31, 1997, treated
by physician operators from 1 of 3 cardiology groups (full-time
Cleveland Clinic staff, Ohio Permanente Medical Group staff,
part-time associate staff) were analyzed. Baseline clinical data were
entered prospectively into an established database, and in-hospital
clinical outcomes were evaluated by a cadre of trained personnel
independent from the physician operators. ECGs were routinely
obtained before and immediately after the procedure, the morning
after the procedure, and in the event of suspected ischemia. Creatine
kinase (CK) levels were routinely assayed 6 to 8 hours after, the
Received April 21, 1999; revision received June 15, 1999; accepted July 13, 1999.
From the Departments of Cardiology (S.G.E., V.G., P.L.W., E.J.T.) and Biostatistics (D.M.), The Cleveland Clinic Foundation, Cleveland, Ohio.
Correspondence to Stephen G. Ellis, MD, The Cleveland Clinic Foundation, 9500 Euclid Ave, F-25, Cleveland, OH 44195. E-mail
[email protected]
© 1999 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
1971
1972
Circulation
November 9, 1999
TABLE 1.
Angiographic Variables
Variable
Bifurcation lesion
Definitions and Conventions
Branch.1.5 mm emanating from within the shoulders of the lesion
Calcification in the target lesion/subdivided into
15Mild: requiring cardiac motion to see; 25moderate: obvious without cardiac motion; 35severe
Calcification in target vessel
Any angiographically apparent calcium in the target vessel
Calcified ($grade 2) and angulated (.45°) lesion
See separate definitions
Chronic total occlusion
Total occlusion (TIMI 0 and 1) with either: (1) known duration $3 mo, or (2) bridging collaterals
Degenerated saphenous vein graft
SVG with $50% of the length of the graft with luminal irregularity, filling defect, gross irregularity, or staining
Filling defect
An angiographic lucency, usually globular, with contrast surrounding at least 3 sides (or equivalent),
divided into 3 grades: 15haziness alone, 25defect 1–2 mm, 35defect .2 mm in diameter
Left ventricular ejection fraction
Assessed by angiography, echo, or gated nuclear scan
Lesion angle
Degrees at end diastole in nonforeshortened view subtended by a 15-mm treatment device
Lesion ectasia
$150% of reference diameter
Lesion irregularity
Irregularly shaped or “sawtooth” lumen edges (cannot be coded as present simultaneously with
thrombus, which takes precedence if both are present)
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Lesion length
Measured shoulder to shoulder
Modified ACC/AHA lesion score2
See Reference 2
Nonchronic total occlusion
Total occlusion not meeting criteria for chronicity (qv)
Normal reference diameter
Diameter of normal-appearing lumen within the same coronary segment (may require averaging
proximal and distal to lesion); if no normal area in the same segment, may be measured from adjacent
segment providing no side branch $1.5 mm is interposed
Number of diseased vessels
Number of coronary arteries with $50% diameter stenosis (left anterior descending, circumflex, or right
coronary arteries; or bypassable branches thereof)
Number of lesions
$50% Diameter stenosis in the target vessel
Ostial location
Within 3 mm of the aorta or major vessel
Plaque mass estimate
Lesion length $50%3%diameter stenosis3normal reference diameter
Proximal tortuosity (old definition)
Moderate52$60° or 1 $90° bend, severe52 or more $90° bends
Proximal tortuosity (trial definition)
Sum of degrees in all bends $60° proximal to target lesion
Restenotic lesion
Lesion previously treated with percutaneous coronary intervention
Saphenous vein graft luminal irregularity
Measured as a percentage of graft length
Saphenous vein graft number of major plaques
Number of $50% stenosis in saphenous vein graft
Saphenous vein graft filling defect
Thrombus or filling defect in a saphenous vein graft
Saphenous vein graft staining
Staining without an apparent thrombus or filling defect in a saphenous vein graft
Saphenous vein graft ectasia
Ectasia (qv) in a saphenous vein graft
Thrombus with staining
Contrast “hangup” in an area of apparent thrombus
morning after the procedure, and in the event of a suspected
myocardial infarction (MI).
clinical interventionists overread by the Cleveland Clinic Core
Angiographic Laboratory in the validation set analysis.
Variables and Definitions
Treatment Variables
Baseline Clinical Variables
Acute MI (,24 hours), age, cardiogenic shock, current smoking,
diabetes mellitus (insulin-dependent and non–insulin-dependent),
gender, hypercholesteremia (total cholesterol $240 mg%, LDL
cholesterol $130 mg%, or HDL cholesterol ,35 mg%), hypertension, New York Heart Association congestive heart failure class,
prior remote MI (.2 weeks), recent MI (1 to 14 days), saphenous
vein graft age (years), and surgically inoperable, unstable angina.
Except for vein graft age (analogous to “chronic” total occlusion in
the ACC/AHA scheme in that it relates a time duration with a
morphological or locating variable), these variables were used for
descriptive purposes only.
Angiographic Variables
See Table 1 for variables assessed and their definitions. Angiographic variables were analyzed by 1 of 2 independent observers
blinded to clinical outcome in the training set analysis and by 1 of 12
Treatment variables were abciximab and primary treatment device
[balloon, directional atherectomy, laser, Rotablator, stent, and transluminal extraction catheter (TEC)].
Outcome Variables
Outcome variables were cardiac death, emergency bypass surgery
(with acute ischemia or for the prevention of acute ischemia within
24 hours of the procedure), and MI [Q-wave and non–Q-wave/
subcategorized by CK level (ECG changes or enzyme elevations
consequent to an acute MI at the patient’s presentation are
excluded)].
Statistical Analysis
Continuous data are presented as mean61 SD if normally distributed
and as median and interquartile range if skewed. Categorical data are
presented as a percentage.
Cases for the training set analysis were composed of all patients
treated during 1995 to 1996 with any ischemic complication and a
Ellis et al
Coronary Morphology and Risk in the Current Era
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randomly selected cohort of patients without complications (3:1
patients with no complications:patients with complications). This
cohort was termed the enriched training set. This approach allowed
us to study characteristics not routinely evaluated without having to
review thousands of cineangiograms. However, if characteristics
were relatively infrequent in this sample (n ,50) and recorded
routinely in our database, the entire 1995 to 1996 data set was used
to ascertain their relation to clinical outcome. Secondary analyses of
the population without the most predictive variables was performed
to improve identification of intermediate-risk lesion morphologies.
Cases for the validation set analysis were composed of all patients
treated during 1997.
Adverse outcomes were characterized as most severe: cardiac
death, Q-wave MI, non–Q-wave MI with CK $53 upper limit of
normal and positive cardiac isoenzymes, or emergency bypass
surgery; severe: non–Q-wave MI with CK elevation 3 to 53 upper
limit of normal in the presence of abnormal cardiac isoenzymes;
moderate: non–Q-wave MI with CK elevation 2 to 33 upper limit of
normal with positive cardiac isoenzymes; uncertain: the presence of
non–Q-wave MI, possibly associated with the lesion evaluated (this
typically occurred when multiple lesions were treated and there was
no obvious angiographic complication); and no complication associated with lesion treatment. Because of the small number of lesions
associated with the severe category in the test population, the most
severe and severe categories were subsequently collapsed for the
purposes of all analyses subsequent to our preliminary investigation.
Stepwise proportional odds logistic regression analysis12 was
performed to identify independent correlates of adverse ischemic
outcomes in the training sample. This, in contradistinction to
standard multiple logistic regression, allows for simultaneous fitting
of a model to a ranked ordinal outcome.
On the basis of their relation to graded adverse outcome, variables
were classified as strongly or moderately correlated. With the use of
the training sample, a scheme to optimize the true-positive, falsenegative relation was developed. The presence of any strong correlate qualified the lesion as highest risk (class IV). The presence of
$3 moderate characteristics qualified the lesion as high risk (class
III), the presence of 1 to 2 moderate characteristics qualified the
lesion as moderate risk (class II), and absence of any risk factor led
to the assessment of low risk (class I).
The predictive capability of the new scheme and the current
ACC/AHA scheme were then tested in the 1997 validation population. Comparison of their predictive capacities were performed with
the use of the methods of Hanley and McNeil.13 Subgroup analyses
were also performed in the 1997 stent-plus-abciximab–treated
population.
All statistical analyses were performed with SYSTAT (SYSTAT
version 7.0, SPSS Inc) or SAS/STAT (SAS Institute Inc, version
6.1).
Results
Patient Population
Baseline patient demographics for the training, validation,
and total population studied are provided in Table 2. Six
thousand three hundred twenty-seven patients and 10 907
lesions in total were analyzed. Patients were typically male
and middle-aged. Sixty-two percent had unstable angina.
Twenty-nine percent had prior bypass surgery. Devices and
drug utilization frequency for the 1995 to 1996 population
were as follows: stents, 40.7% (planned in 36.9% and bailout
in 3.8%); abciximab, 26.2% (planned in 24.0% and bailout in
2.2%); Rotablator, 18.9%; directional coronary atherectomy,
0.9%; excimer laser coronary angioplasty, 0.2%; and TEC,
0.2%. The figures for the 1997 population were as follows:
stent, 64.2% (62.6% planned and 1.6% bailout); abciximab,
41.1% (38.4% planned, 2.7% bailout); Rotablator, 17.7%;
directional coronary atherectomy, 0.6%; excimer laser coro-
TABLE 2.
1973
Baseline Patient Demographics
1995–1996
1997
Total
4181
2146
6327
5.9
7.3
6.4
63611
63611
63611
Cardiogenic shock, %
1.4
1.4
1.4
Congestive heart failure class II–IV, %
4.7
4.9
4.8
Current smoking, %
18.6
21.0
19.4
Diabetes mellitus, %
26.2
26.8
26.4
No.
Acute MI, %
Age, y
Hypercholesterolemia, %
43.7
55.0
47.5
Hypertension, %
58.2
63.9
60.1
Left ventricular ejection fraction, %
55612
53613
54612
Male sex, %
70.9
70.8
70.9
Multivessel disease, %
63.4
65.2
64.6
Prior bypass surgery, %
29.7
29.2
29.5
Prior MI, %
52.5
53.4
52.8
Prior restenosis, %
14.5
13.4
14.1
Recent MI, %
14.5
16.0
15.0
1.5
1.3
1.4
1.2
1.9
1.5
Surgically inoperable, %
Target artery(ies)
Left main trunk, %
Left anterior descending, %
36.8
35.2
36.2
Right coronary artery, %
33.7
32.4
33.2
Left circumflex, %
28.3
30.4
29.1
61.7
63.3
62.2
Unstable angina, %
nary angioplasty, 0.5%; and TEC, 0.1%. No significant
differences were observed between the training and validation samples except for the use of stents and abciximab.
Clinical Outcomes
For the training and validation cohorts together, technical
success achieved at $1 target sites was achieved in 95.8% of
patients, and major complications (death, Q-wave MI, or
emergency bypass surgery) occurred in 1.9% of patients
(Table 3). There was no significant difference between the
training and validation sets for any major outcome.
Training Sample Evaluation
In the enriched training sample, there were 85 lesions
associated with “most severe” complications, 11 lesions
associated with “severe” complications, 93 lesions associated
with “moderately severe” complications, and 57 lesions
TABLE 3.
In-Hospital Outcome
1995–1996
1997
Total
No. of treated sites
1.66.9
1.66.9
1.66.9
Technical success*
95.6
96.2
95.8
Death, %
1.1
0.9
1.0
Emergency CABG, %
0.9
1.0
0.9
Q-wave MI, %
0.3
0.4
0.3
Non–Q-wave MI, %
5.9
5.1
5.6
*Reduction to ,50% diameter stenosis and establishment of TIMI 3 flow at
$1 target site.
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Circulation
November 9, 1999
TABLE 4. Preprocedural Lesion Correlates of Ischemic Complications in the
Training Sample
Univariate*
Variable
Multivariate*
P
OR
P
OR
Nonchronic total occlusion‡
3.71 (2.22–6.30)
,0.001
4.74 (2.69–8.38)
,0.001
Degenerated SVG§
5.21 (3.33–8.14)
,0.001
4.18 (2.39–7.31)
,0.001
Length $20 mm†‡
2.41 (1.36–4.29)
0.003
2.77 (1.51–5.09)
0.001
Irregularity‡
2.04 (1.46–2.83)
,0.001
1.88 (1.32–2.66)
,0.001
Large filling defect§
4.02 (2.55–6.35)
,0.001
1.41 (1.17–1.70)
,0.001
Length 10–20 mm†‡
1.61 (1.10–2.35)
0.014
1.88 (1.26–2.82)
0.002
Moderate calcium1angle\
3.65 (1.19–11.14)
0.023
4.44 (1.24–15.96)
0.022
Eccentric\
1.65 (0.97–2.81)
0.067
2.12 (1.09–4.12)
0.027
Severe calcification§
1.84 (0.88–3.80)
0.088
2.19 (1.04–4.57)
0.046
SVG age $10 y‡
5.61 (2.46–12.78)
,0.001
1.81 (1.00–3.31)
0.051
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SVG indicates saphenous vein graft.
*OR and P values in the enriched and overall samples are not directly comparable.
†For combined variable lesion length $10 mm, univariate OR51.67 (1.23–2.26), P50.001, and
multivariate OR51.96 (1.34 –3.01), P50.001.
‡From enriched dataset (improving the separation of high-risk from moderate-risk lesions
somewhat).
§From overall dataset.
\Multivariate analysis data from sample excluding highest-risk lesion (univariate data from
enriched dataset).
associated with “possible” complications (a total of 246
adverse event–related lesions). This number increased to 257
in the full evaluation consequent to our inability to retrieve
cineangiograms on 7 patients (11 lesions) associated with
complications during the analysis of the enriched training
sample.
As can be seen in Table 4, 10 variables were identified as
independent correlates of graded adverse outcome. Detailed
clinical outcomes for the 2 most important correlates in the
entire 1995 to 1997 cohort were for nonchronic total occlusion: death, 4.5%; Q-wave infarction, 0.1%; emergency
bypass surgery, 2.8%; non–Q-wave infarction, 5.2% (CK
.53 0.6%, CK 3 to 53 3.9%, CK 2 to 33 0.7%); for
degenerated saphenous vein grafts: death, 1.1%; Q-wave
infarction, 2.8%; emergency bypass surgery, 0.4%; non–Qwave infarction, 12.7% (CK .53 1.5%, CK 3 to 53 8.8%,
CK 2 to 33 2.4%). The proposed schema derived from this
analysis is presented in Figure 1 (the 2 lesion length variables
were combined). The c-statistic evaluating the predictive
value of the new model for complications in the training set
was 0.701.
Validation Sample Evaluation
Performance of the new model in the 1997 validation sample
is shown in Table 5 and Figure 2. The calibration coefficient
(r) for the relation between risk in the training and validation
samples for each risk group (Figure 2) is 0.971. The c-statistic
for the new model was 0.672 (the c-statistic for the ACC/
AHA scheme was 0.620, P50.010). The new model had its
predictive accuracy maintained in the prespecified
stent1abciximab subset (c-statistic50.663), whereas by the
ACC/AHA scheme, the c-statistic was only 0.589.
Discussion
The ACC/AHA lesion risk classification schema has been
criticized because of its subjectivity and because it emanates
TABLE 5.
Criteria-Outcome Relations in the Validation Set
n
Non–Q-Wave
MI 2–33CK
Death, MI $33CK, or
Emergency CABG
A
1278
3.3
2.5
B1
1482
5.4
3.0
B2
849
9.5
5.2
C
622
7.4
6.6
Class I (low)
2241
4.0
2.1
Class II (moderate)
1487
5.2
3.4
52
6.7
8.2
421
8.1
12.7
ACC/AHA
New model
Class III (high)
Figure 1. New risk assessment schema based on the current
analysis. SVG indicates saphenous vein graft.
Class IV (highest)
Ellis et al
Coronary Morphology and Risk in the Current Era
Figure 2. Calibration of new model with 1997 outcome data.
Class IV (HH) indicates highest risk; class III (H), high risk; class
II (M), moderate risk; and class I (L), low risk. ECABG indicates
emergency CABG.
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from an era when stents and glycoprotein IIb/IIIa inhibitors in
particular were not available. Nonetheless, in the hands of
core angiographic laboratories and in those practitioners who
are both objective and well versed in its meaning, this system
has been demonstrated repeatedly to have predictive power in
the assessment of risk for populations of patients.14 –16
Our comprehensive reevaluation of the relation between
lesion morphology and short-term outcome with percutaneous intervention was undertaken with several goals and
considerations. First, we wanted to develop and validate a
better predictive instrument suitable for the current era of
intervention. We expected that changes in treatment and
outcome might attenuate the correlation of some previously
important lesion characteristics with outcome. We intended to
make use of inferences from observations with the use of
intracoronary ultrasound and angioscopy17–19 to postulate
new or modified angiographic characteristics to evaluate. We
recognized, however, that prediction of risk generally becomes more difficult as overall risk diminishes (as it has in
the decade since the modified ACC/AHA scheme was developed). Second, we hoped to more objectively characterize
certain angiographic risk factors to lessen the subjectivity of
the risk assessment. Third, we wanted for the first time to
have a system that reflected the gradation of clinically
meaningful adverse events.20 Fourth, we hoped that the new
instrument would be relatively simple and easy to implement.
The proposed classification scheme is, in fact, more predictive than the prior modified ACC/AHA lesion scheme,
although perhaps not by as much as one might have suspected
beforehand. Importantly, it was validated in a patient population reflecting current utilization practice (stenting in 64%,
glycoprotein IIb/IIIa inhibitors in 41%), and maintained its
predictive accuracy in the patient populations treated with
stents and ReoPro (c-statistic50.66). In addition, it is somewhat simpler than the previous system analyzing 9 specific
elements instead of 16. Further, we were able to more
specifically define the nature of certain characteristics evaluated. Previous definitions that were particularly troublesome
due to their subjectivity included that for degenerated vein
grafts, calcification, and proximal tortuosity.
Also important, particularly as it pertains to the assessment
of individual patient risk, is the absence of importance of
1975
certain characteristics that were previously thought to be
associated with heightened risk. These include lesion angulation per se, bifurcation location, ostial location, proximal
tortuosity, and small thrombus. It is likely that improvements
in device profile and trackability, as well as the capacity for
stenting to treat dissections that were particularly prone to
develop with balloon angioplasty in certain circumstances,
account for these differences.
In addition, the identification of specific lesion characteristics that continue to be associated with complications, even
with current therapies, provides objective data from which to
challenge industry to improve percutaneous treatment devices
and adjunct pharmacology. The importance of aged and
degenerated vein graft lesion morphology in particular should
heighten interest in the development of treatments that may
minimize the risk of complications associated with treatment
of such lesions, for example, emboli entrapment devices and
covered stents. The association of nonchronic total occlusion
with adverse outcome is partly due to its correlation with the
setting of acute MI and the subsequent risk of cardiac death;
hence it may be less modifiable. Nonetheless, if patients with
acute MI were excluded from analysis, this variable maintains
considerable independent prognostic power (OR53.60,
P50.003 [compare with Table 4]).
There are 2 limitations in particular that should be noted in
relation to this analysis. First, although the model was
prospectively validated in a population representative of
currently treated patients, one must be somewhat cautious
about overgeneralizing the results. The results were derived
from outcomes of 18 generally experienced interventionists
operating in an environment when senior operator assistance
was readily available. Annual interventional patient volume
of these operators ranged from 42 to 323 over this 3-year
period. In addition, the assessment of lesion morphology was
performed by angiographers who were trained and highly
experienced. Second, although from a statistical standpoint
this model provides considerable predictive power, it is far
from perfect. Certainly, clinical factors such as patient age,
presentation with acute MI, or poor left ventricular function,
as well as operator characteristics,21–23 even in the era of stent
utilization, would be expected to affect outcome and therefore
diminish the sole predictive capability of lesion morphology.
In the end, any measure of the relation between lesion
characteristics and outcome in this setting, although somewhat helpful in the choice of potential therapies for a given
patient, will always have greater power in assessing the risk
of large populations.
In conclusion, utilization of this contemporary risk assessment algorithm by interventionists working under similar
circumstances should improve their assessment of patient
risk, and, in particular, extend availability of percutaneous
intervention to some patients who otherwise would have been
turned down for treatment because of perceived high risk.
Acknowledgment
The authors would like to acknowledge the expert assistance of Patti
Durnwald in the preparation of the manuscript.
1976
Circulation
November 9, 1999
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Circulation. 1999;100:1971-1976
doi: 10.1161/01.CIR.100.19.1971
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