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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 5, September/October 2018
AFRICA
281
35%.
10
Operators tend to overestimate severe stenosis, whereas
modest stenosis is underestimated.
11
In our study, we found a moderate degree of concordance
between visual operators in the categories 70–89 and 90–99%.
There was a low degree of concordance between visual operators
in the categories
<
50 and 50–69%. These results show that
especially in cases of moderate and low degree of stenosis, inter-
observer variability increases.
QCA of coronary stenosis eliminates inter-observer bias
and enables reproducible measurements. QCA is also useful
for prediction of coronary restenosis after different coronary
interventional techniques.
12
It may also be used to follow the
natural course of atherosclerosis. A decrease in the minimal
lumen diameter and an increase in the percentage diameter of
stenosis determined by QCA in follow-up coronary angiography
was associated with increased coronary events. Change in
minimal lumen diameter was the strongest predictor of coronary
events.
13
When we compared the results of visual estimation with
QCA, we found significant differences between visual estimation
and QCA in percentage diameter of stenosis and percentage area
of stenosis. We also found differences between implanted stent
diameter and reference diameter calculated by QCA and between
stent length and lesion length derived from QCA. That means
there is variability between implanted stent diameter and length
and true size of the lesion. Physicians tended to implant larger
and longer stents. The difference between mean diameter of
implanted stent and mean reference diameter was 0.22 mm and
the difference inmean length of the implanted stent and the lesion
was 1.79 mm. Although statistically significant, this difference
was not so great as to cause clinically important consequences.
The important point is to cover the whole atherosclerotic
segment with an optimal sized stent. Theoretically, choosing a
longer stent size may increase the risk of stent restenosis in the
future.
Twenty-three lesions considered significant according to visual
estimation were found not to be significant when determined by
QCA. This means that approximately 15% of patients, or one in
seven, underwent unnecessary intervention.
When comparing the difference between percentage diameter
of stenosis and percentage area of stenosis in determining the
severity of stenosis, there was a statistically significant difference
between the QCA-derived parameters (58.4
±
14.5 vs 80.6
±
11.2%). Percentage area of stenosis had a low to moderate grade
of concordance with visual estimation, whereas there was no
concordance between percentage diameter of stenosis and visual
estimation. Percentage diameter of stenosis may underestimate
the lesion.
In a study by Gottsauner-Wolf
et al
., it was shown that
percentage area of stenosis more closely reflected the visual
estimation of lesion severity than percentage diameter of
stenosis.
14
In another study, the authors used dobutamine stress
echocardiography to determine the cut-off values of QCA
parameters in estimation of the functional significance of
coronary lesions. Angiographic cut-off values were determined
as ≤ 1.07 mm, ≥ 75% and ≥ 52% for minimal lumen diameter,
percentage area of stenosis and percentage diameter of stenosis,
respectively. The cut-off value for percentage diameter of
stenosis was much less than the cut-off value for percentage area
of stenosis.
15
Similar to the results of our study, percentage area
of stenosis was prone to underestimate the lesion if the cut-off
value was accepted as 70%. If percentage diameter of stenosis is
used as QCA parameter, it may be more suitable to accept the
cut-off value as 50%.
There are a few early trials comparing visual assessment
with QCA. Older QCA software systems did not have the
technology that we have today.
2-8
Modern QCA software systems
have advanced digital technology enabling more accurate and
complex assessment.
There is only one recent study comparing visual assessment
of severity of coronary lesions and QCA measurement. In this
study, similar to our study, Nallamothu
et al
. showed that visual
assessment tended to overestimate the lesion more than QCA.
Inconsistency between QCA and visual assessment was high,
especially in cases of moderately severe coronary lesions.
9
QCA is a non-invasive and cheap method of quantification of
coronary stenosis and measurement of reference vessel diameter
for deciding the size of the stent. Despite its limitations, such as
vessel foreshortening, it enables well-correlated measurements of
lesion length, minimal lumen diameter and reference diameter. It
also may prevent unnecessary PCI.
Conclusion
Visual estimation may overestimate a coronary lesion and may
lead to unnecessary coronary intervention. There was low
concordance in the categories
<
50% and 50–69% between the
operators. Percentage area of stenosis had a low to moderate
grade of concordance with visual estimation. Percentage area
of stenosis more closely reflected the visual estimation of lesion
severity than percentage diameter of stenosis.
References
1.
Gensini GG, Kelly AE, Da Costa BCB. Quantitative angiography: the
measurement of coronary vasomobility in the intact animal and man.
Chest
1971;
60
: 522–530.
Table 5. Comparison of concordance between visual estimation and
percentage area of stenosis with kappa analysis
Visual percentage
of stenosis
Percentage area of stenosis by QCA,
n
(%)
Kappa
p
-value
50
–
69% 70
–
89% 90
–
99% Total
50
–
69%
2 (33.3) 4 (66.7) 0 (0)
6 (100)
0.300 0.000**
70
–
89%
17 (22.7) 53 (70.7) 5 (6.7) 75 (100)
90
–
99%
6 (8.1) 32 (43.2) 36 (48.6) 74 (100)
Total
25 (15.6) 89 (57.8) 41 (26.6) 155 (100)
**
p
<
0.01.
Table 6. Comparison of concordance between visual estimation and
percentage diameter of stenosis with kappa analysis
Visual percentage
of stenosis
Percentage diameter of stenosis by QCA,
n
(%)
Kappa
p
-value
< 50% 50–69% 70–89% 90–99%
< 50%
0 (0)
0 (0)
0 (0)
0 (0)
–0.061 0.000**
50–69%
3 (50)
3 (50)
0 (0)
0 (0)
70–89%
29 (53) 42 (56)
4 (38.7) 0 (0)
90–99%
11 (14.9) 31 (41.9) 27 (36.5) 5 (6.8)
Total
43 (27.7) 76 (49.0) 31 (20.0) 5 (3.2)
**
p
<
0.01.