3.1 Clinical and Procedural Characteristics
A total of 53 patients with calcified lesions on coronary angiography were enrolled who underwent stent implantation with the guidance of OCT and had complete pre- or post-stent OCT images. 33 patients (34 lesions) were finally included after excluding the patients with in-stent restenosis and OCT images unable to analyze due to either poor-quality or lacking important frames (Figure 1).
The mean age of the patients was 67 ± 10 years, with 20 male. More than 70% of the patients had the coexisting hypertension and hyperlipidemia. The patients diagnosed with stable angina pectoris were 7 (21.2%) whereas acute coronary syndrome were 26 (78.8%). Poor stent expansion occurred in 22 patients (23 lesions). The age of the patients was significantly older (70 ± 10 vs 59 ± 8, p = 0.003) and the estimated glomerular filtration rate was significantly lower (82.16 vs 93.95, p = 0.036) in the stent underexpansion group. There was no significant difference with regard to remaining clinical characteristics between two groups (Table 1).
Table 1. Clinical characteristics of the patients
Variables
|
Poor expansion (n = 22)
|
Adequate expansion (n = 11)
|
P-value
|
Age (year)
|
70 ± 10
|
59 ± 8
|
0.003
|
Male, n (%)
|
12 (54.5%)
|
8 (72.7%)
|
0.456
|
BMI (kg/m2)
|
25.91 ± 3.80
|
25.08 ± 1.58
|
0.496
|
Hypertension, n (%)
|
16 (72.7%)
|
7 (63.6%)
|
0.696
|
Diabetes, n (%)
|
10 (45.5%)
|
4 (36.4%)
|
0.719
|
Hyperlipidemia, n (%)
|
16 (72.7%)
|
9 (81.8%)
|
0.687
|
CKD, n (%)
|
2 (9.1%)
|
1 (9.1%)
|
1.000
|
Smoking, n (%)
|
8 (36.4%)
|
6 (54.5%)
|
0.534
|
Family history of CHD, n (%)
|
4 (18.2%)
|
5 (45.5%)
|
0.121
|
Prior PCI, n (%)
|
8 (36.4%)
|
4 (36.4%)
|
1.000
|
Clinical diagnosis, n (%)
|
|
|
1.000
|
Stable angina
|
5 (22.7%)
|
2 (18.2%)
|
|
UA
|
13 (59.1%)
|
7 (63.6%)
|
|
Acute MI
|
4 (18.2%)
|
2 (18.2%)
|
|
LVEF (%)
|
69.03 ± 5.71
|
66.32 ± 6.04
|
0.298
|
LDL-C (mmol/L)
|
2.06 ± 0.77
|
2.06 ± 0.53
|
0.992
|
FPG (mmol/L)
|
5.08 (4.52, 5.58)
|
5.07 (4.72, 6.10)
|
0.620
|
eGFR (ml/min/1.73 m2)
|
82.16 (71.37, 93.25)
|
93.95 (90.52, 104.00)
|
0.036
|
Abbreviations: BMI, body mass index; CKD, chronic kidney disease; CHD, coronary heart disease; PCI, percutaneous coronary intervention; UA, unstable angina; MI, myocardial infarction; LVEF, left ventricular ejection fraction; LDL-C, low density lipoprotein-cholesterol; FPG, fasting plasma glucose; eGFR, estimated glomerular filtration rate.
Values are presented as number (%), mean ± standard deviation, or median (interquartile range).
RA was used in the modification of 19 (55.9%) lesions. The lesions treated with scoring or non-compliant balloon prior to stent deployment were both 13 (38.2%). The average amount of the stent implanted was 2 and the total length of stents was 44 mm. Compared with the patients in the adequate stent expansion group, the rate of RA performed during PCI was significantly higher in the patients with stent underexpansion (73.9% vs 18.2%, p = 0.003) (Table 2).
Table 2. Procedural characteristics of the lesions
Variables
|
Poor expansion (n = 23)
|
Adequate expansion (n = 11)
|
P-value
|
Scoring balloon, n (%)
|
11 (47.8%)
|
2 (18.2%)
|
0.245
|
Maximum pressure (atm)
|
14.00(11.00, 15.00)
|
12.00(12.00, 12.00)
|
0.545
|
Maximum diameter (mm)
|
2.75(2.50, 2.88)
|
2.50(2.38, 2.62)
|
0.351
|
Non-compliant balloon, n (%)
|
11 (47.8%)
|
2 (18.2%)
|
0.245
|
Maximum pressure (atm)
|
18.00(17.00, 24.00)
|
13.50(12.75, 14.25)
|
0.091
|
Maximum diameter (mm)
|
2.50(2.50, 2.50)
|
2.25(2.12, 2.38)
|
0.098
|
Semi-compliant balloon, n (%)
|
18 (78.3%)
|
8 (72.7%)
|
1.000
|
Maximum pressure (atm)
|
16.00(14.00, 16.00)
|
15.00(13.50, 16.50)
|
0.686
|
Maximum diameter (mm)
|
2.50(2.12, 2.50)
|
2.50(2.38, 2.50)
|
0.885
|
RA, n (%)
|
17 (73.9%)
|
2 (18.2%)
|
0.003
|
Times of RA
|
5(3, 7)
|
5(4, 5)
|
0.893
|
Maximum burr size (mm)
|
1.50(1.38, 1.50)
|
1.50(1.50, 1.50)
|
0.725
|
Speed of burr (r/min)
|
15.00(15.00, 16.00)
|
16.60(15.90, 17.30)
|
0.212
|
Stent
|
|
|
|
Number of stent
|
2(1, 3)
|
1(1, 2)
|
0.126
|
Total stent length (mm)
|
48.00(37.50, 69.00)
|
32.00(28.00, 57.00)
|
0.197
|
Maximum diameter (mm)
|
3.00(2.75, 3.00)
|
2.75(2.50, 3.00)
|
0.165
|
Abbreviations: RA, rotational atherectomy.
Values are presented as number (%), or median (interquartile range).
3.2 Imaging Analysis of Calcified Plaques
The majority of patients had multi-vessel disease. The target lesions were mainly located in the left anterior descending artery. The prevalence of moderate and severe coronary calcification assessed by angiography was up to 88.2% (30 lesions). All parameters of QCA analysis were comparable between two groups (Table 3).
Table 3. QCA analyses of calcified lesions
Variables
|
Poor expansion (n = 23)
|
Adequate expansion (n = 11)
|
P-value
|
Pre-procedure
|
|
|
|
Multivessel disease, n (%)
|
19 (82.6%)
|
11 (100.0%)
|
0.280
|
Target vessel, n (%)
|
|
|
1.000
|
Left anterior descending
|
19 (82.6%)
|
9 (81.8%)
|
|
Left circumflex
|
1 (4.3%)
|
0 (0.0%)
|
Right coronary artery
|
3 (13.0%)
|
2 (18.2%)
|
Degree of calcification, n (%)
|
|
|
0.362
|
None or mild
|
2 (8.7%)
|
2 (18.2%)
|
|
Moderate
|
14 (60.9%)
|
8 (72.7%)
|
Severe
|
7 (30.4%)
|
1 (9.1%)
|
Bifurcation, n (%)
|
2 (8.7%)
|
4 (36.4%)
|
0.070
|
Angulation, n (%)
|
|
|
0.203
|
<90°
|
22 (95.7%)
|
10 (90.9%)
|
|
>90°
|
1 (4.3%)
|
1 (9.1%)
|
|
Calcium length (mm)
|
35.77 ± 20.66
|
26.03 ± 12.34
|
0.227
|
RVD (mm)
|
2.63(2.38, 2.83)
|
2.54(2.32, 2.64)
|
0.597
|
MLD (mm)
|
1.24 ± 0.42
|
1.33 ± 0.33
|
0.579
|
Diameter stenosis (%)
|
53.43 ± 13.27
|
48.02 ± 12.92
|
0.290
|
Post-procedure
|
|
|
|
RVD (mm)
|
2.39(2.12, 2.53)
|
2.50(2.26, 2.94)
|
0.155
|
MSD (mm)
|
2.19(2.02, 2.44)
|
2.33(2.02, 2.74)
|
0.382
|
Diameter stenosis (%)
|
11.58(6.45, 15.02)
|
10.71(6.80, 15.51)
|
0.887
|
Abbreviations: QCA, quantitative coronary angiography; RVD, reference vessel diameter; MLD, minimum lumen diameter; MSD, minimum stent diameter.
Values are presented as number (%), mean ± standard deviation, or median (interquartile range).
There was a good concordance between two observers for the interpretation of OCT images and the assessment of maximum calcium arc (ICC = 0.877), thickness (ICC = 0.874) and length (ICC = 0.968). The lesions all manifested as superficial calcification, with the median maximum calcium arc 230°, median maximum calcium length 25.10 mm and average maximum calcium thickness 1.18 mm, respectively. The overall final post-PCI stent expansion was 70.74%. Notably, the maximum calcium arc (299° vs 142°, p < 0.001) and thickness (1.24 mm vs 1.04 mm, p = 0.029) were larger in the poor stent expansion group, while the pre-stent diameter stenosis obtained from OCT (52.76% vs 66.29%, p = 0.038) was lower. The proportion of stent malapposition increased significantly in the poor stent expansion group (60.9% vs 9.1%, p = 0.011) (Table 4).
Table 4. OCT data of calcified lesions
Variables
|
Poor expansion (n = 23)
|
Adequate expansion (n = 11)
|
P-value
|
Pre-stent
|
|
Superficial calcium, n (%)
|
23 (100%)
|
11 (100%)
|
-
|
Maximum calcium length (mm)
|
33.15(15.62, 40.20)
|
20.65(14.78, 25.10)
|
0.094
|
Maximum calcium arc (°)
|
299(205, 345)
|
142(104, 216)
|
0.001
|
Maximum calcium thickness (mm)
|
1.24 ± 0.23
|
1.04 ± 0.25
|
0.029
|
Minimum lumen area (mm2)
|
1.64(1.16, 2.28)
|
2.26(1.65, 2.71)
|
0.217
|
Reference vessel area (mm2)
|
6.47(5.08, 8.20)
|
5.30(5.11, 6.92)
|
0.429
|
Diameter stenosis (%)
|
52.76(45.59, 58.58)
|
66.29(55.66, 71.74)
|
0.038
|
Area stenosis (%)
|
81.73(80.06, 83.37)
|
84.11(82.44, 86.80)
|
0.063
|
Post-stent
|
|
Tissue prolapse, n (%)
|
1 (4.3%)
|
0 (0%)
|
1.000
|
Stent edge dissection, n (%)
|
0 (0%)
|
0 (0%)
|
-
|
Stent malapposition, n (%)
|
13 (60.9%)
|
1 (9.1%)
|
0.011
|
Minimum stent area (mm²)
|
4.25(3.96, 5.62)
|
5.42(4.60, 6.77)
|
0.146
|
Reference vessel area (mm2)
|
8.02(6.43, 9.09)
|
5.90(5.33, 8.64)
|
0.217
|
Stent expansion (%)
|
63.39 ± 12.72
|
86.10 ± 4.59
|
<0.001
|
Abbreviations: OCT, optical coherence tomography.
Values are presented as number (%), mean ± standard deviation, or median (interquartile range).
3.3 Development of Calcium Scoring System
The age, utilization of RA, maximum calcium arc, thickness, length and diameter stenosis from OCT significantly correlated with stent expansion. After adjustment of the potential confounding factors, the age (OR: 1.173, 95% CI: 1.036~1.438, p = 0.042) and maximum calcium arc (OR: 1.023, 95% CI: 1.008~1.050, p = 0.021) were found to be the independent predictors of stent underexpansion in the multivariate logistic regression model (Table 5). Based on these results, we established a novel calcium scoring system as: 0.16 × age + 0.03 × maximum calcium arc.
Table 5. Multivariate logistic regression model of stent underexpansion
Variables
|
β-coefficient
|
Odds Ratio
|
95% CI
|
P-value
|
Age (year)
|
0.159
|
1.173
|
1.036 ~ 1.438
|
0.042
|
Maximum calcium arc (°)
|
0.023
|
1.023
|
1.008 ~ 1.050
|
0.021
|
Abbreviations: CI, confidence interval.
We then identified the optimal threshold for the prediction of stent underexpansion by ROC curve analysis. The best cut-off value for the scoring system was 16.87 (sensitivity 0.870, specificity 0.909, AUC 0.925, 95% CI: 0.836~1.014, p < 0.001) (Figure 2). Representative OCT images were shown in Figure 3.
3.4 Comparison with Previous Scoring System
Compared with the calcium scoring system proposed by Fujino, the novel system according to the age and maximum calcium arc had better performance for the prediction of stent underexpansion in the present study population, with a significantly larger AUC of ROC (0.925 vs 0.706, p = 0.002) (Figure 2).