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Abstract

Aims

Optical coherence tomography (OCT)-guided external elastic lamina (EEL)-based stent sizing is safe and as effective as intravascular ultrasound in achieving post-procedural lumen dimensions. However, when compared with automated lumen diameter (LD) measurements, this approach is time-consuming. We aimed to compare vessel diameter measurements and stent diameter selection using either of these approaches and examined whether applying a correction factor to automated LD measurements could result in selecting similar stent diameters to the EEL-based approach.

Methods and results

We retrospectively compared EEL-based measurements vs. automated LD in reference segments in 154 OCT acquisitions and derived a correction factor for stent sizing using the ratio of EEL to LD measurements. We then prospectively applied the correction factor in 119 OCT acquisitions. EEL could be adequately identified in 100 acquisitions (84%) at the distal reference to allow vessel diameter measurement. Vessel diameters were larger with EEL-based vs. LD measurements at both proximal (4.12 ± 0.74 vs. 3.14 ± 0.67 mm, P < 0.0001) and distal reference segments (3.34 ± 0.75 vs. 2.64 ± 0.65 mm, P < 0.0001). EEL-based downsizing led to selection of larger stents vs. an LD-based upsizing approach (3.33 ± 0.47 vs. 2.70 ± 0.44, P < 0.0001). Application of correction factors to LD [proximal 1.32 (IQR 1.23–1.37) and distal 1.25 (IQR 1.19–1.36)] resulted in discordance in stent sizing by >0.25 mm in 63% and potentially hazardous stent oversizing in 41% of cases.

Conclusion

EEL-based stent downsizing led to selection of larger stent diameters vs. LD upsizing. While applying a correction factor to automated LD measurements resulted in similar mean diameters to EEL-based measurements, this approach cannot be used clinically due to frequent and potentially hazardous stent over-sizing.

optical coherence tomography, stent sizing, intravascular imaging

Introduction

When compared with intravascular ultrasound (IVUS), that enables visualization of the external elastic lamina (EEL) behind most atherosclerotic lesions, the limited penetration depth of light emitted in optical coherence tomography (OCT) results in frequent loss of visualization of EEL.1,2 Thus, in contrast to IVUS, most studies of OCT-guided percutaneous coronary intervention (PCI) have used luminal dimensions in lieu of the ‘true’ vessel size, i.e. EEL-based diameter, for selection of stent diameters. This approach has resulted in selecting smaller stent diameters and thereby smaller final minimum stent areas (MSA) compared with either IVUS- or angiography-guided stenting.1,3,4 Since post-PCI MSA is a critical determinant of freedom from early and late major adverse cardiovascular events (MACE) after stenting,5–12 smaller lumen dimensions measured on OCT may be a major limitation of this imaging modality, possibly offsetting benefits afforded by its superior resolution in guiding PCI procedures.

The ILUMIEN III randomized trial demonstrated that OCT-guided EEL-based stent sizing was feasible, safe, and as effective in achieving similar MSA as IVUS, and led to greater minimal and mean stent expansion compared with angiography, and the least number of untreated procedural complications.13 Nevertheless, EEL-based measurements on OCT are performed manually, are time-consuming, and require specific training and experience. In contrast, automated mean lumen diameter (LD) measurement is a simple, readily available feature on commercial OCT systems, yet it has the aforementioned limitation of leading to selection of undersized stents.

We sought to determine the magnitude of difference between the EEL- and automated LD-based selection of stent diameters. We also examined whether deriving and applying a correction factor for LD (LDCorr) may provide guidance in selecting stent diameters that are similar to the EEL-based measurements, thus obviating the need to manually search for and measure the EEL-based diameter.

Methods

Study design and participants

In a retrospective set of 154 OCT acquisitions from the ILUMIEN III study, we manually measured the mean EEL to EEL diameter at the proximal and distal reference segments where at least 180° of reference vessel EEL could be visualized. Greater than 180° of EEL could be visualized at either reference segment in 85% of cases, 69% at the proximal reference vessel and 77% at the distal reference. We then recorded the proximal and distal reference mean LD from the OCT automated measurements at the exact same location. We undertook hypothetical stent sizing by using the distal reference vessel measurements (i) rounding down the mean distal EEL reference diameter to the nearest device size for EEL-based stent sizing and (ii) rounding up the mean distal LD to the nearest device size for LD-based stent sizing. Using the reference vessel EEL and LD measurements, we derived a correction factor for vessel sizing by calculating the ratio of EEL to LD measurements (LDCorr) at both the proximal and distal references. For validation of LDCorr, we prospectively scanned 119 consecutive patients undergoing OCT for clinical indication at two centers (Columbia University Medical Center, New York, NY, USA and St. Francis Hospital, Roslyn, NY, USA). Greater than 180° of EEL could be visualized at either reference segment in 92 (77%) cases, but in 100 acquisitions (84%) at the distal reference. We applied the LDCorr in the validation cohort by multiplying the respective proximal- and distal-derived correction factors to the mean LD of the proximal and distal reference vessels. We then compared these calculations to the actual EEL-based measurements of the reference segments (LDCorr vs. EEL). We subsequently undertook hypothetical stent sizing by using the distal reference vessel measurements (i) rounding down the mean distal EEL reference diameter to the nearest device size for EEL-based stent sizing and (ii) rounding up the LD to the nearest device size for LD-based stent sizing (Figures 1 and 2). We then compared the stent sizing based on the calculated vs. actual EEL-based reference diameters: i.e. we compared the LDCorr × mean distal LD rounded down to ∼0.25 mm with the EEL-based distal diameter rounded down to ∼0.25 mm.

EEL vs. lumen-based device sizing. (A) OCT cross-section shows an automated minimal and maximal lumen diameters of 2.99 and 3.36 mm, respectively, with mean lumen diameter of 3.15 mm. Using a lumen-based sizing strategy, rounding up leads to the choice of a 3.25 mm device. (A′) The EEL (yellow dashed line) is visible for >270° allowing measurement of EEL minimal and maximal diameters of 4.34 and 4.83 mm respectively. The mean EEL-EEL diameter is 4.59 mm. Using an EEL-based sizing strategy, rounding down leads to the choice of a 4.5 mm device. The difference in device size choice based on the lumen vs. EEL is 1.25 mm. (B) OCT cross-section shows an automated minimal and maximal lumen diameters of 1.80 and 2.43 mm, respectively, with mean lumen diameter of 2.18 mm. Using a lumen-based sizing strategy, rounding up leads to the choice of a 2.25 mm device. (B′) The EEL (yellow dashed line) is visible for <270° allowing measurement of a single EEL diameter of 3.25 mm. Using an EEL-based sizing strategy, leads to choice of a 3.25 mm device. The difference in device size choice based on the lumen vs. EEL is 1 mm. (C) OCT cross-section shows an automated minimal and maximal lumen diameters of 2.72 and 3.28 mm, respectively, with mean lumen diameter of 2.98 mm. Using a lumen-based sizing strategy, rounding up leads to the choice of a 3.0 mm device. (C′) The EEL (yellow dashed line) is visible for <90° not allowing measurement of EEL vessel diameters. EEL, external elastic lamina; OCT, optical coherence tomography.
Figure 1

EEL vs. lumen-based device sizing. (A) OCT cross-section shows an automated minimal and maximal lumen diameters of 2.99 and 3.36 mm, respectively, with mean lumen diameter of 3.15 mm. Using a lumen-based sizing strategy, rounding up leads to the choice of a 3.25 mm device. (A′) The EEL (yellow dashed line) is visible for >270° allowing measurement of EEL minimal and maximal diameters of 4.34 and 4.83 mm respectively. The mean EEL-EEL diameter is 4.59 mm. Using an EEL-based sizing strategy, rounding down leads to the choice of a 4.5 mm device. The difference in device size choice based on the lumen vs. EEL is 1.25 mm. (B) OCT cross-section shows an automated minimal and maximal lumen diameters of 1.80 and 2.43 mm, respectively, with mean lumen diameter of 2.18 mm. Using a lumen-based sizing strategy, rounding up leads to the choice of a 2.25 mm device. (B′) The EEL (yellow dashed line) is visible for <270° allowing measurement of a single EEL diameter of 3.25 mm. Using an EEL-based sizing strategy, leads to choice of a 3.25 mm device. The difference in device size choice based on the lumen vs. EEL is 1 mm. (C) OCT cross-section shows an automated minimal and maximal lumen diameters of 2.72 and 3.28 mm, respectively, with mean lumen diameter of 2.98 mm. Using a lumen-based sizing strategy, rounding up leads to the choice of a 3.0 mm device. (C′) The EEL (yellow dashed line) is visible for <90° not allowing measurement of EEL vessel diameters. EEL, external elastic lamina; OCT, optical coherence tomography.

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Methods to determine device size using EEL, lumen, and LDcorr. (A) Greater than 180° of EEL are visible. The EEL–EEL diameter measures 3.25 mm (white bar). The mean EEL diameter rounded down determines the device size (3.0 mm). (B) Less than 180° of EEL are visible, thus the OCT mean lumen diameter is used to determine device diameter. The mean lumen diameter is 2.89 mm. The mean lumen diameter rounded up determines the device size (3.0 mm). (C) Less than 180° of EEL are visible. The OCT mean lumen diameter is multiplied by the respective correction factor (in this case distal, thus 1.25) and used to determine the device diameter. The mean lumen diameter is multiplied by the correction factor to mimic EEL sizing, and rounded down to determine the device size (3.5 mm). Note that the MLDcorr (white bar—3.61 mm) is still smaller than the true EEL-EEL diameter (4.03 mm). EEL, external elastic lamina; MLDCorr, minimal lumen diameter—corrected; OCT, optical coherence tomography.
Figure 2

Methods to determine device size using EEL, lumen, and LDcorr. (A) Greater than 180° of EEL are visible. The EEL–EEL diameter measures 3.25 mm (white bar). The mean EEL diameter rounded down determines the device size (3.0 mm). (B) Less than 180° of EEL are visible, thus the OCT mean lumen diameter is used to determine device diameter. The mean lumen diameter is 2.89 mm. The mean lumen diameter rounded up determines the device size (3.0 mm). (C) Less than 180° of EEL are visible. The OCT mean lumen diameter is multiplied by the respective correction factor (in this case distal, thus 1.25) and used to determine the device diameter. The mean lumen diameter is multiplied by the correction factor to mimic EEL sizing, and rounded down to determine the device size (3.5 mm). Note that the MLDcorr (white bar—3.61 mm) is still smaller than the true EEL-EEL diameter (4.03 mm). EEL, external elastic lamina; MLDCorr, minimal lumen diameter—corrected; OCT, optical coherence tomography.

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Procedures

We performed pre-PCI OCT after administration of intracoronary nitroglycerin through a guiding catheter (≥6F). We performed OCT via femoral or radial access using unfractionated heparin or bivalirudin anticoagulation per the operator preference. We acquired the OCT images using the Dragonfly OPTIS Imaging Catheter (Abbott Vascular, Santa Clara, CA, USA). The EEL-based measurements were independently performed by two cardiologists with extensive experience in OCT analysis (Y.P. and E.S.).

Statistical analysis

Statistical analyses were performed with SPSS version 20.0 (IBM, Armonk, NY, USA). Normally distributed continuous variables are reported as mean with SD and compared with the Student’s t-test; continuous variables not exhibiting normal distribution are reported as median with first and third quartiles and compared with the Mann–Whitney U test. Categorical variables are summarized as numbers (percentages) and compared using χ2 statistics or Fisher’s exact test, as appropriate. The 95% confidence interval (CI) was calculated for the difference in proportions between groups. A P-value <0.05 was considered statistically significant.

Results

Baseline demographic, procedural and OCT characteristics of the derivation and validation cohorts are presented in Table 1.

Table 1
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Demographic and procedural characteristics

Derivation, (n = 154)Validation (n = 100)P-value
Demographic
 Age (years)65.5 ± 9.364.4 ± 11.00.49
 Male109 (69)66 (66)0.62
 Hypertension124 (78)83 (83)0.37
 Dyslipidaemia115 (73)73 (73)0.97
 Diabetes52 (33)42 (42)0.14
 Prior coronary artery bypass grafting3 (1.9%)5 (5)0.16
 Silent ischaemia6 (4)4 (4)0.99
 Stable angina54 (34)31 (31)0.60
 Unstable angina72 (46)43 (43)0.87
 NSTEMI20 (13)16 (16)0.43
 STEMI6 (3.8)6 (6.0)0.55*
Procedural
 Target vessel
  Left anterior descending80 (51)63 (63)0.048
  Left circumflex43 (27)22 (22)0.39
  Right35 (22)15 (15)0.12
OCT
 Proximal EEL (mm)4.12 ± 0.744.08 ± 0.660.89
 Proximal LD (mm)3.14 ± 0.673.14 ± 0.610.93
 Distal EEL (mm)3.34 ± 0.753.44 ± 0.580.75
 Distal LD (mm)2.64 ± 0.662.68 ± 0.530.81
Derivation, (n = 154)Validation (n = 100)P-value
Demographic
 Age (years)65.5 ± 9.364.4 ± 11.00.49
 Male109 (69)66 (66)0.62
 Hypertension124 (78)83 (83)0.37
 Dyslipidaemia115 (73)73 (73)0.97
 Diabetes52 (33)42 (42)0.14
 Prior coronary artery bypass grafting3 (1.9%)5 (5)0.16
 Silent ischaemia6 (4)4 (4)0.99
 Stable angina54 (34)31 (31)0.60
 Unstable angina72 (46)43 (43)0.87
 NSTEMI20 (13)16 (16)0.43
 STEMI6 (3.8)6 (6.0)0.55*
Procedural
 Target vessel
  Left anterior descending80 (51)63 (63)0.048
  Left circumflex43 (27)22 (22)0.39
  Right35 (22)15 (15)0.12
OCT
 Proximal EEL (mm)4.12 ± 0.744.08 ± 0.660.89
 Proximal LD (mm)3.14 ± 0.673.14 ± 0.610.93
 Distal EEL (mm)3.34 ± 0.753.44 ± 0.580.75
 Distal LD (mm)2.64 ± 0.662.68 ± 0.530.81

Values are n (%) or mean ± SD.

EEL, external elastic lamina; LD, lumen diameter; NSTEMI, non–ST-elevation myocardial infarction; OCT, optical coherence tomography; STEMI, ST-elevation myocardial infarction.

Table 1
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Demographic and procedural characteristics

Derivation, (n = 154)Validation (n = 100)P-value
Demographic
 Age (years)65.5 ± 9.364.4 ± 11.00.49
 Male109 (69)66 (66)0.62
 Hypertension124 (78)83 (83)0.37
 Dyslipidaemia115 (73)73 (73)0.97
 Diabetes52 (33)42 (42)0.14
 Prior coronary artery bypass grafting3 (1.9%)5 (5)0.16
 Silent ischaemia6 (4)4 (4)0.99
 Stable angina54 (34)31 (31)0.60
 Unstable angina72 (46)43 (43)0.87
 NSTEMI20 (13)16 (16)0.43
 STEMI6 (3.8)6 (6.0)0.55*
Procedural
 Target vessel
  Left anterior descending80 (51)63 (63)0.048
  Left circumflex43 (27)22 (22)0.39
  Right35 (22)15 (15)0.12
OCT
 Proximal EEL (mm)4.12 ± 0.744.08 ± 0.660.89
 Proximal LD (mm)3.14 ± 0.673.14 ± 0.610.93
 Distal EEL (mm)3.34 ± 0.753.44 ± 0.580.75
 Distal LD (mm)2.64 ± 0.662.68 ± 0.530.81
Derivation, (n = 154)Validation (n = 100)P-value
Demographic
 Age (years)65.5 ± 9.364.4 ± 11.00.49
 Male109 (69)66 (66)0.62
 Hypertension124 (78)83 (83)0.37
 Dyslipidaemia115 (73)73 (73)0.97
 Diabetes52 (33)42 (42)0.14
 Prior coronary artery bypass grafting3 (1.9%)5 (5)0.16
 Silent ischaemia6 (4)4 (4)0.99
 Stable angina54 (34)31 (31)0.60
 Unstable angina72 (46)43 (43)0.87
 NSTEMI20 (13)16 (16)0.43
 STEMI6 (3.8)6 (6.0)0.55*
Procedural
 Target vessel
  Left anterior descending80 (51)63 (63)0.048
  Left circumflex43 (27)22 (22)0.39
  Right35 (22)15 (15)0.12
OCT
 Proximal EEL (mm)4.12 ± 0.744.08 ± 0.660.89
 Proximal LD (mm)3.14 ± 0.673.14 ± 0.610.93
 Distal EEL (mm)3.34 ± 0.753.44 ± 0.580.75
 Distal LD (mm)2.64 ± 0.662.68 ± 0.530.81

Values are n (%) or mean ± SD.

EEL, external elastic lamina; LD, lumen diameter; NSTEMI, non–ST-elevation myocardial infarction; OCT, optical coherence tomography; STEMI, ST-elevation myocardial infarction.

Derivation cohort

While the mean LD highly correlated with the EEL-based diameter at the proximal reference (R2 = 0.74, P < 0.0001), the mean LD was significantly smaller than the EEL-based diameter (3.14 ± 0.67 vs. 4.12 ± 0.74, P < 0.0001; Figure 3A), with an absolute difference of 0.96 ± 0.32 mm, 95% CI 0.89–1.02. Similarly, at the distal reference, the mean LD also highly correlated with the EEL-based diameter (R2 = 0.74, P < 0.0001), and the mean LD was smaller than the EEL-based diameter (2.64 ± 0.65 vs. 3.34 ± 0.76, P < 0.0001; Figure 3B), with an absolute difference of 0.71 ± 0.43 mm, 95% CI 0.63–0.79. Accordingly, stent sizing based on the distal reference mean LD upsized to the nearest device size led to selection of significantly smaller stent diameters compared with EEL-based downsizing to the nearest device size (2.70 ± 0.44 vs. 3.33 ± 0.47, P < 0.0001; Figure 3C). Mean LD-based stent selection led to stent under-sizing in 91% of cases compared with the EEL-based measurement.

Scatterplot comparing mean lumen diameter with external elastic lamina-derived measurements and stent sizing. Scatterplot comparing (A) the proximal reference mean lumen diameter with external elastic lamina-derived measurements, (B) the distal reference mean lumen diameter with external elastic lamina-derived measurements, and (C) the stent diameter by lumen-derived measurements with the stent diameter by external elastic lamina-derived measurements. The line of best fit is in blue with the associated shaded error bands in grey.
Figure 3

Scatterplot comparing mean lumen diameter with external elastic lamina-derived measurements and stent sizing. Scatterplot comparing (A) the proximal reference mean lumen diameter with external elastic lamina-derived measurements, (B) the distal reference mean lumen diameter with external elastic lamina-derived measurements, and (C) the stent diameter by lumen-derived measurements with the stent diameter by external elastic lamina-derived measurements. The line of best fit is in blue with the associated shaded error bands in grey.

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The magnitude of differences between the mean LD and EEL-based diameters at the proximal and distal reference segments and in stent sizing is shown in Table 2. The mean EEL-based size was larger by ∼1 mm in the proximal reference and 0.75 mm in the distal reference. When hypothetical stent sizing was performed based on distal EEL-based downsizing vs. LD-based upsizing, the stent diameters were undersized by LD-based measurement in the majority of the cases, by ≥0.25 mm in 10%, by ≥0.50 mm in 34%, by ≥0.75 mm in 31%, and by 1 mm in 16% of the reference segments, with the selected stent diameters being equal with either of the strategies in only 9% of the reference segments. LDCorr was calculated to be 1.32 (IQR 1.23–1.37) in the proximal reference and 1.25 (IQR 1.19–1.36) in the distal reference.

Table 2
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Lumen vs. external elastic lamina-based measurements

Lumen (n = 100)External elastic lamina (n = 84)P-Value
Proximal reference
 Mean vessel diameter (mm)3.14 ± 0.674.12 ± 0.74<0.0001
Distal reference
 Mean vessel diameter (mm)2.64 ± 0.653.34 ± 0.76<0.0001
Stent diameter
 Mean lumen diameter (mm)2.70 ± 0.443.33 ± 0.47<0.0001
 Undersized by ≥0.25 mm10 (10)0 (0)<0.0001
 Undersized by ≥0.50 mm34 (34)0 (0)<0.0001
 Undersized by ≥0.75 mm31 (31)0 (0)<0.0001
 Undersized by ≥1.00 mm16 (16)0 (0)<0.0001
Lumen (n = 100)External elastic lamina (n = 84)P-Value
Proximal reference
 Mean vessel diameter (mm)3.14 ± 0.674.12 ± 0.74<0.0001
Distal reference
 Mean vessel diameter (mm)2.64 ± 0.653.34 ± 0.76<0.0001
Stent diameter
 Mean lumen diameter (mm)2.70 ± 0.443.33 ± 0.47<0.0001
 Undersized by ≥0.25 mm10 (10)0 (0)<0.0001
 Undersized by ≥0.50 mm34 (34)0 (0)<0.0001
 Undersized by ≥0.75 mm31 (31)0 (0)<0.0001
 Undersized by ≥1.00 mm16 (16)0 (0)<0.0001

Values are n (%) or mean ± SD.

Table 2
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Lumen vs. external elastic lamina-based measurements

Lumen (n = 100)External elastic lamina (n = 84)P-Value
Proximal reference
 Mean vessel diameter (mm)3.14 ± 0.674.12 ± 0.74<0.0001
Distal reference
 Mean vessel diameter (mm)2.64 ± 0.653.34 ± 0.76<0.0001
Stent diameter
 Mean lumen diameter (mm)2.70 ± 0.443.33 ± 0.47<0.0001
 Undersized by ≥0.25 mm10 (10)0 (0)<0.0001
 Undersized by ≥0.50 mm34 (34)0 (0)<0.0001
 Undersized by ≥0.75 mm31 (31)0 (0)<0.0001
 Undersized by ≥1.00 mm16 (16)0 (0)<0.0001
Lumen (n = 100)External elastic lamina (n = 84)P-Value
Proximal reference
 Mean vessel diameter (mm)3.14 ± 0.674.12 ± 0.74<0.0001
Distal reference
 Mean vessel diameter (mm)2.64 ± 0.653.34 ± 0.76<0.0001
Stent diameter
 Mean lumen diameter (mm)2.70 ± 0.443.33 ± 0.47<0.0001
 Undersized by ≥0.25 mm10 (10)0 (0)<0.0001
 Undersized by ≥0.50 mm34 (34)0 (0)<0.0001
 Undersized by ≥0.75 mm31 (31)0 (0)<0.0001
 Undersized by ≥1.00 mm16 (16)0 (0)<0.0001

Values are n (%) or mean ± SD.

Validation cohort

There was no significant difference in the LD or EEL-based measurements in the proximal or distal reference segments between the derivation and validation cohorts (Table 1). When the proximal correction factor was applied to the proximal LD in the validation cohort, mean vessel diameter was similar between the EEL-based measurements and the corrected LD (4.08 ± 0.66 vs. 4.14 ± 0.80, P = 0.56; R2 = 0.74, P < 0.0001; Figure 4A). Similarly, applying the correction factor to the distal LD resulted in corrected LDs that were similar to the EEL-based diameters (3.44 ± 0.58 vs. 3.34 ± 0.67, P = 0.29; R2 = 0.74, P < 0.0001; Figure 4B). However, stent sizing based on corrected LD led to discordance of the chosen stent size when compared with EEL-based sizing by at least 0.25 mm in 63% of cases (P < 0.001). Furthermore, using the corrected LD led to stent oversizing in 41% of cases (by 0.25 mm in 22%, 0.50 mm in 13%, 0.75 mm in 3%, and 1.0 mm in 3%; P < 0.001; Figure 4C).

Scatterplot comparing the corrected mean lumen diameter with the external elastic lamina-derived measurements and stent sizing. Scatterplot comparing (A) the corrected mean lumen diameter with the external elastic lamina-derived measurements at the proximal reference, (B) the corrected mean lumen diameter with the external elastic lamina-derived measurements at the distal reference, and (C) the stent diameter by corrected lumen-derived measurements with the stent diameter by external elastic lamina-derived measurements. The line of best fit is in blue with the associated shaded error bands in grey.
Figure 4

Scatterplot comparing the corrected mean lumen diameter with the external elastic lamina-derived measurements and stent sizing. Scatterplot comparing (A) the corrected mean lumen diameter with the external elastic lamina-derived measurements at the proximal reference, (B) the corrected mean lumen diameter with the external elastic lamina-derived measurements at the distal reference, and (C) the stent diameter by corrected lumen-derived measurements with the stent diameter by external elastic lamina-derived measurements. The line of best fit is in blue with the associated shaded error bands in grey.

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Discussion

In the current study, we investigated the differences between the mean LD and EEL-based measurements by OCT and how these differences may impact stent sizing. We report a number of clinically relevant findings. First, at the proximal reference segment, the mean difference between the mean LD and EEL-based diameters was ∼1 mm, while at the distal reference segment the mean difference was ∼0.75 mm. Secondly, as opposed to the LD-based stenting, EEL-based stent sizing led to the selection of a larger diameter stent in >90% of cases; on average this difference was >0.5 mm. Thirdly, while using a corrected LD-based measurement is a practical approach, potentially obviating the need for manual EEL-based measurement, its application led to discordance in stent sizing in more than half of the cases, with potentially hazardous oversizing in 41% of cases.

While OCT provides high-resolution cross-sectional images of the plaque microarchitecture, the penetration depth of OCT is limited, potentially limiting visualization of the entire vessel wall. As a result, a perception has prevailed that measurements requiring visualization of the EEL—including vessel diameter, area, and plaque burden—cannot be reliably performed with OCT. This perception has led to a widespread adoption of the lumen-based stent sizing by OCT. The consequence of such a strategy is a smaller post-PCI MSA compared with both angiography and IVUS. In the ILUMIEN I study, angiography guidance during PCI led to a larger MSA compared with lumen-based OCT guidance.3 Subsequently, multiple studies have shown that IVUS-guided PCI, based on vessel wall measurements, leads to larger MSAs compared with lumen-based measurements with OCT guidance during PCI.1,14,15 Given that the MSA is the most consistent and strongest predictor of PCI outcomes,11,12,16–22 OCT may be disadvantaged compared with IVUS due to differences in stent sizing strategy. Nevertheless, a specific OCT-guided EEL-based stent optimization strategy in the randomized ILUMIEN III trial was safe and resulted in similar MSA to that of IVUS-guided PCI with a trend towards larger MSA compared with angiography guidance and the least number of untreated PCI complications.13 Critically, despite the aforementioned perceptions, there was no difference in the ability to identify >180° of EEL between OCT (84%) and IVUS (83%) in the ILUMIEN III study.

In the current study, we show that the EEL-based diameter is consistently larger than the mean LD at both the proximal and distal reference segments. While this finding in and of itself is rather obvious, it is the magnitude of the difference that has the potential to impact PCI strategy. At the proximal reference, the difference between the EEL-based diameter and mean LD was ∼1 mm and at the distal reference ∼0.75 mm. These large differences translate directly into meaningful differences in the choice of stent size, with a direct impact on the final MSA. Indeed, even when employing a strategy of upsizing from the mean LD measurements compared with downsizing from the EEL-based measurements at the distal reference to guide the choice of the stent diameter, the mean difference in stent size was well >0.5 mm in diameter.

Despite the positive results of the ILUMIEN III trial, the OCT-guided EEL-based sizing strategy has not been widely adopted, with concerns regarding the ability to consistently visualize the EEL at reference segments, lack of automated measurements, and effects on workflow quoted as the likely reasons. As such, utilizing a lumen-based correction factor has the potential to significantly improve the workflow and eliminate operator errors in measurement. Unfortunately, our data suggest that a correction factor applied to the automated LD cannot safely estimate the EEL-based dimensions for stent sizing. We therefore recommend following the algorithmic OCT-guided EEL-based stent sizing strategy as described in the ILUMIEN III trial.23 The long-term benefits of applying this strategy are currently being assessed in the ongoing ILUMIEN IV: OPTIMAL PCI trial (NCT03507777).

Based on the current study, in practice, EEL-based measurements should be used wherever possible for stent sizing (expected to be feasible in majority, i.e. >80%, of cases) and LD-based measurements with rounding up only used when EEL-based measurements are not feasible. After measurement of stent diameter and length, the angiographic co-registration function should be utilized for positioning stents at the intended segments to improve placement precision and reduce geographic miss. If OCT angiography co-registration is not available, a cine angiogram must be acquired during the OCT pullback so that the OCT frames can be correlated with the angiogram with the help of the fiduciary landmarks (e.g. side branches, calcium deposits, and previous stents).

Limitations

The prospective component of this a study was conducted at two high-volume institutions by experienced OCT operators. As a small number of patients were included in this study, large-scale prospective randomized trials would be needed to demonstrate that EEL-based stenting is practical in a clinical setting and leads to improved clinical outcomes. Future studies need to assess the incidence and impact of intravascular imaging on stent under- and over-sizing. Alternative more sophisticated algorithms to generate a correction factor were not attempted and may have improved the predictive performance. In the future, artificial intelligence-based algorithms may be able to automatically detect the EEL where visible, thus obviating the need for a correction factor.

Conclusions

The application of an EEL-based stent sizing strategy results in larger stent size selection compared with a mean LD-guided stent sizing strategy. A universally applicable correction factor for LD cannot be recommended to replace OCT-guided EEL-based measurements for stent sizing.

Funding

The ILUMIEN III trial was funded by St. Jude Medical (now Abbott).

Conflict of interest: E.S. is a consultant: Abbott Vascular and Opsens. M.M. is a consultant: Terumo Corporation. A.M. received grant support from Abbott Vascular and Boston Scientific, consultant for Conavi Medical Inc. G.S.M. is a honoraria: Boston Scientific, Philips, Terumo, and Medtronic. A.J. received Institutional grant support and consultant: Philips/Volcano and Abbott Vascular. G.W.S. received research grants: Abbott; speaker honoraria: Terumo, Amaranth, and Novartis; consultant: Shockwave, Valfix, TherOx, Reva, Vascular Dynamics, Robocath, HeartFlow, Gore, Ablative Solutions, Matrizyme, Miracor, Neovasc, V-wave, Abiomed, Claret, Sirtex, MAIA Pharmaceuticals, SpectraWave, and Ancora; and equity/options: Ancora, Qool Therapeutics, Cagent, Applied Therapeutics, Biostar family of funds, MedFocus family of funds, SpectraWave, Orchestra Biomed, and Aria. Z.A.A. received Institutional research grants to Columbia University: Abbott and Cardiovascular Systems Inc.; consultant: Abbott, Amgen, Astra Zeneca, and Boston Scientific; and equity: Shockwave Medical. Other authors report no conflict of interest.

Data availability

The data underlying this article are available in the article.

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