We sought to determine the outcome with undersized drug-eluting stents for percutaneous coronary intervention of saphenous vein graft lesions. Using intravascular ultrasound guidance, 209 saphenous vein graft lesions were treated with drug-eluting stents (153 sirolimus-eluting and 56 paclitaxel-eluting stents). The lesions were divided into 3 groups according to the ratio of the stent diameter to the average intravascular ultrasound reference lumen diameter: group I, <0.89; group II, 0.9 to 1.0; and group III, >1.0. Angiographic no-reflow was defined as a Thrombolysis In Myocardial Infarction flow grade of 0, 1, and 2 after percutaneous coronary intervention. Plaque intrusion was defined as tissue extrusion through the stent struts. Stent malapposition was defined as one or more stent struts that had clearly separated from the vessel wall with evidence of blood speckles behind the strut. No significant differences were found in the use of distal protection devices (group I, 44%; group II, 35%; and group III, 36%; p = 0.5); and no significant differences were found in the incidence of stent malapposition among the 3 groups (group I, 21%; group II, 42%; and group III, 52%; p = 0.001). The plaque intrusion area (group I, 0.13 ± 0.30 mm 2 ; group II, 0.25 ± 0.42 mm 2 ; and group III, 0.31 ± 0.40 mm 2 ; p = 0.018) and plaque intrusion volume (group I, 0.25 ± 0.68 mm 3 ; group II, 0.40 ± 0.68 mm 3 ; and group III, 0.75 ± 1.34 mm 3 ; p = 0.007) were smallest in group I. The plaque intrusion area and plaque intrusion volume correlated with the ratio of the stent diameter to the average intravascular ultrasound reference lumen diameter (r = 0.278, p <0.001 and r = 0.283, p <0.001, respectively). The incidence of a creatine kinase-MB elevation >3 times normal was 6% in group I, 9% in group II, and 19% in group III (p = 0.025). No significant differences were found in the incidence of 1-year target lesion revascularization (group I, 13%; group II, 9%; and group III, 15%; p = 0.5) or target vessel revascularization (group I, 13%; group II, 13%; and group III, 15%; p = 0.9) among the 3 groups. In conclusion, the use of undersized drug-eluting stents to treat patients with saphenous vein graft lesions is associated with a reduction in the frequency of post-percutaneous coronary intervention creatine kinase-MB elevation without an increase in 1-year events.
Percutaneous coronary intervention (PCI) for saphenous vein graft (SVG) disease is widely performed in patients with coronary artery disease. However, PCI of SVG stenoses is accompanied by less favorable short- and long-term outcomes compared to PCI of native coronary arteries. PCI of SVG disease is limited by distal embolization and no-reflow. Distal embolization is a frequent complication of PCI in degenerated SVGs, resulting in creatine kinase-MB elevation and occasional significant myocardial infarction. In-stent restenosis is more frequent in SVGs than in native coronary arteries. Larger post-PCI minimum stent areas, as measured by intravascular ultrasound (IVUS) guidance, are associated with lower rates of in-stent restenosis in native coronary arteries. However, a previous study has shown that aggressive stent expansion in SVG lesions resulted in greater myocardial infarction rates and, unlike in native arteries, no improvement in the target vessel revascularization rate at 1 year. We had observed that PCI of SVGs using stents smaller than the diameter of the SVG (as measured with IVUS guidance) was associated with less embolic material retrieved from the distal protection device used and no apparent worsening of the long-term outcome in terms of myocardial infarction, cardiac death, or target lesion and target vessel revascularizations. The purpose of the present study was to compare the efficacy of undersize versus normal-size stents on the clinical outcomes of PCI in SVG lesions.
Methods
We reviewed the records of 209 patients who had undergone successful IVUS-guided PCI with drug-eluting stents for 209 SVG lesions and who had undergone post-PCI IVUS examinations at our institution from March 2002 to December 2005. We excluded patients with restenotic SVG lesions, patients with subacute stent thrombosis, patients with cardiogenic shock, and patients in whom adequate IVUS images could not be obtained. Of the 209 patients, 153 were treated with sirolimus-eluting stents and 56 with paclitaxel-eluting stents. The lesions were divided into 3 groups according to the ratio of the stent diameter to the average IVUS reference lumen diameter: group I, <0.89 (n = 71); group II, 0.9 to 1.0 (n = 71); and group III, >1.0 (n = 67). A small group of 21 patients had a ratio <0.70. The institutional review board approved the protocol. The hospital records of all the patients were reviewed to obtain information on the clinical demographics and medical history.
No-reflow was defined as Thrombolysis In Myocardial Infarction grade 0, 1, and 2 flow in the absence of mechanical obstruction after PCI. Normal reflow was defined as Thrombolysis In Myocardial Infarction grade 3 flow on the final post-PCI angiograms. If the Thrombolysis In Myocardial Infarction flow grade after PCI was 0, 1, or 2 despite the absence of angiographic stenosis, a repeat IVUS examination was performed to exclude the possibility of mechanical vessel obstruction.
Quantitative analysis (CAAS II, Pie Medical Imaging, Maastricht, The Netherlands) was performed using standard protocols. Using the outer diameter of the contrast-filled catheter as the calibration standard, the reference diameter and minimal lumen diameter were measured in diastolic frames from orthogonal projections. Perfusion was evaluated according to the Thrombolysis In Myocardial Infarction criteria. All IVUS examinations were performed after intra-SVG administration of 200 μg nitroglycerin using a commercially available IVUS system (Boston Scientific/SCIMed, Minneapolis, Minnesota). The IVUS catheter was advanced distal to the target lesion, and imaging was performed retrograde to the aorto-ostial junction at an automatic pullback speed of 0.5 mm/s.
The quantitative and qualitative analyses were performed according to the American College of Cardiology clinical expert consensus document on standards for acquisition, measurement, and reporting of IVUS studies. Before PCI, we measured the SVG and lumen cross-sectional area using planimetry software (TapeMeasure, INDEC Systems, Mountain View, California). The SVG cross-sectional area was measured by tracing the outer border of the entire vein graft using previously described methods. The plaque cross-sectional area was calculated as the SVG cross-sectional area minus the lumen cross-sectional area, and the plaque burden was calculated as the plaque cross-sectional area divided by the SVG cross-sectional area. The lesion site was the cross-sectional slice with the smallest lumen; if multiple image slices had the same minimum lumen cross-sectional area, the image slice with the largest SVG and plaque was measured. Soft plaque was less bright than the adventitia, fibrotic plaque was as bright as, or brighter than, the adventitia without acoustic shadowing, and calcific plaque was brighter than the adventitia with acoustic shadowing. When no dominant plaque composition was noted, the plaque was classified as mixed. The remodeling index was the ratio of the lesion site SVG cross-sectional area divided by the average of the proximal and distal reference SVG cross-sectional areas.
After PCI, we measured the minimum stent cross-sectional area. Stent expansion was calculated as the minimum stent cross-sectional area divided by the mean reference lumen cross-sectional area. Plaque intrusion was defined as tissue extrusion through the stent strut after PCI, and the volume of plaque intrusion was calculated by subtracting the lumen volume from the stent volume. Stent malposition was defined as one or more stent struts clearly separated from the vessel wall with evidence of blood speckles behind the strut. Major adverse cardiac events included cardiac death, target lesion or target vessel revascularization, and myocardial infarction. All deaths were considered of cardiac origin unless a noncardiac origin had been established clinically or at autopsy. Target lesion revascularization was defined as repeat revascularization within the stent or within the 5-mm borders proximal and distal to the stent on the follow-up angiogram. Target vessel revascularization was defined as repeat revascularization within the treated SVG. Myocardial infarction was defined as ischemic symptoms associated with cardiac enzyme elevation of ≥3 times the upper limit of normal.
The Statistical Package for Social Sciences for Windows, version 15.0 (SPSS, Chicago, Illinois) was used for all analyses. Continuous variables are presented as the mean value ± SD and were compared using paired or unpaired Student’s t test or the nonparametric Wilcoxon test if the normality assumption was violated. Discrete variables are presented as percentages and relative frequencies. Linear regression analysis was used to evaluate the associations between maximum plaque intrusion area and plaque intrusion volume versus the ratio of stent diameter to the average IVUS reference lumen diameter. A p value <0.05 was considered statistically significant.
Results
An example of undersize drug-eluting stent implantation for large SVGs is shown in Figure 1 . The baseline characteristics are summarized in Table 1 . The ratio of the stent diameter to the average IVUS reference lumen diameter was 0.83 ± 0.06 in group I, 0.94 ± 0.03 in group II, and 1.10 ± 0.11 in group III. No significant differences were found in age, clinical presentation, risk factors for coronary artery disease, graft age, or in the use of distal protection devices, bivalirudin, or glycoprotein IIb/IIIa inhibitors among the 3 groups. The angiographic findings and procedural results are summarized in Table 2 . An ostial lesion was most frequently observed in group III. No significant differences were found in the diseased vessel, pre-PCI Thrombolysis In Myocardial Infarction flow grade, stent type, stent diameter, stent length, pre-PCI minimum lumen diameter, or post-PCI minimum lumen diameter among the 3 groups. However, the inflation pressure during stenting was lowest and the reference diameter was greatest in group I.
| Variable | Ratio of Stent Diameter to Average IVUS Reference Lumen Diameter | p Value | ||
|---|---|---|---|---|
| <0.89, Group I (n = 71) | 0.9–1.0, Group II (n = 71) | >1.0, Group III (n = 67) | ||
| Stent diameter/average reference lumen diameter | 0.83 ± 0.06 | 0.94 ± 0.03 | 1.10 ± 0.11 | <0.001 |
| Age (years) | 71 ± 10 | 68 ± 11 | 68 ± 11 | 0.14 |
| Men | 52 (73%) | 53 (75%) | 52 (78%) | 0.8 |
| Clinical presentation | 0.5 | |||
| Stable angina pectoris | 19 (27%) | 20 (28%) | 26 (39%) | |
| Unstable angina pectoris | 42 (59%) | 42 (59%) | 32 (48%) | |
| Non–ST-segment elevation myocardial infarction | 10 (14%) | 8 (11%) | 9 (13%) | |
| ST-segment elevation myocardial infarction | 0 | 1 (1%) | 0 | |
| Diabetes mellitus | 18 (25%) | 22 (31%) | 25 (37%) | 0.3 |
| Systemic hypertension | 41 (58%) | 43 (61%) | 44 (66%) | 0.2 |
| Smoker | 33 (47%) | 20 (28%) | 29 (43%) | 0.059 |
| Hypercholesterolemia ⁎ | 61 (86%) | 57 (80%) | 56 (84%) | 0.7 |
| Family history of coronary disease | 15 (21%) | 20 (28%) | 19 (28%) | 0.5 |
| Graft age (years) | 11 ± 7 | 12 ± 7 | 10 ± 7 | 0.4 |
| Ejection fraction (%) | 53 ± 11 | 55 ± 10 | 56 ± 11 | 1.0 |
| Distal protection device use | 31 (44%) | 25 (35%) | 24 (36%) | 0.5 |
| Bivalirudin use | 67 (94%) | 68 (96%) | 62 (93%) | 0.7 |
| Glycoprotein IIb/IIIa inhibitor use | 9 (13%) | 8 (11%) | 14 (21%) | 0.2 |
⁎ Included patients with previously documented diagnosis of hypercholesterolemia treated with diet or medication; a new diagnosis could have been made during present hospitalization by an elevated total cholesterol level >160 mg/d; category did not include elevated triglycerides.
| Variable | Ratio of Stent Diameter to Average IVUS Reference Lumen Diameter | p Value | ||
|---|---|---|---|---|
| <0.89, Group I (n = 71) | 0.9–1.0, Group II (n = 71) | >1.0, Group III (n = 67) | ||
| Saphenous vein graft narrowed | 0.8 | |||
| Saphenous vein graft to left anterior descending artery | 14 (20%) | 16 (23%) | 12 (18%) | |
| Saphenous vein graft to left circumflex artery | 28 (39%) | 25 (35%) | 30 (45%) | |
| Saphenous vein graft to right | 29 (41%) | 30 (42%) | 25 (37%) | |
| Lesion site | 0.010 | |||
| Ostium | 13 (18%) | 10 (14%) | 20 (30%) | |
| Proximal | 15 (21%) | 29 (41%) | 22 (33%) | |
| Middle | 19 (27%) | 16 (23%) | 10 (15%) | |
| Distal | 20 (28%) | 13 (18%) | 7 (10%) | |
| Anastomosis | 4 (6%) | 3 (4%) | 8 (12%) | |
| Pre-percutaneous coronary intervention thrombolysis in myocardial infarction flow grade | 0.15 | |||
| 0 | 6 (9%) | 1 (1%) | 2 (3%) | |
| 1 | 0 | 0 | 1 (2%) | |
| 2 | 11 (16%) | 6 (9%) | 11 (16%) | |
| 3 | 54 (76%) | 64 (90%) | 53 (79%) | |
| Stent type | 0.4 | |||
| Sirolimus eluting | 48 (68%) | 53 (75%) | 52 (78%) | |
| Paclitaxel eluting | 23 (32%) | 18 (25%) | 15 (22%) | |
| Stent diameter (mm) | 3.1 ± 0.4 | 3.2 ± 0.3 | 3.2 ± 0.3 | 0.2 |
| Stent length (mm) | 22 ± 7 | 21 ± 7 | 22 ± 8 | 0.8 |
| Direct stenting | 54 (76%) | 51 (72%) | 48 (72%) | 0.8 |
| Inflation pressure (atm) | 13 ± 3 | 14 ± 3 | 15 ± 3 | 0.001 |
| Post-percutaneous coronary intervention thrombolysis in myocardial infarction flow grade | 0.2 | |||
| 0 | 1 (1%) | 0 | 0 | |
| 1 | 0 | 0 | 0 | |
| 2 | 6 (9%) | 6 (9%) | 12 (18%) | |
| 3 | 64 (90%) | 65 (92%) | 55 (82%) | |
| Reference diameter (mm) | 4.2 ± 0.7 | 3.7 ± 0.6 | 3.0 ± 0.5 | <0.001 |
| Pre-minimal lumen diameter (mm) | 0.7 ± 0.4 | 0.5 ± 0.4 | 0.5 ± 0.3 | 0.2 |
| Post-minimal lumen diameter (mm) | 3.0 ± 0.5 | 3.2 ± 0.7 | 3.1 ± 0.6 | 0.4 |
The IVUS results are summarized in Table 3 . The reference and lesion site SVG, lumen, and plaque cross-sectional area were greatest and the stent expansion was smallest in group I. No significant difference was found in the incidence of stent malapposition among the 3 groups. However, plaque intrusion was observed least frequently ( Figure 2 ). The plaque intrusion area (group I, 0.13 ± 0.30 mm 2 ; group II, 0.25 ± 0.42 mm 2 ; and group III, 0.31 ± 0.40 mm 2 ; p = 0.018) and plaque intrusion volume (group I, 0.25 ± 0.68 mm 3 ; group II, 0.40 ± 0.68 mm 3 ; and group III, 0.75 ± 1.34 mm 3 ; p = 0.007) were smallest in group I. The plaque intrusion area and plaque intrusion volume correlated with the ratio of the stent diameter to the average IVUS reference lumen diameter (r = 0.278, p <0.001, and r = 0.283; p <0.001, respectively; Figure 3 ).
| Variable | Ratio of Stent Diameter to Average IVUS Reference Lumen Diameter | p Value | ||
|---|---|---|---|---|
| <0.89, Group I (n = 71) | 0.9–1.0, Group II (n = 71) | >1.0, Group III (n = 67) | ||
| Reference | ||||
| Saphenous vein graft cross-sectional area (mm 2 ) | 17.2 ± 5.4 | 14.0 ± 4.7 | 11.2 ± 4.2 | <0.001 |
| Lumen cross-sectional area (mm 2 ) | 11.4 ± 3.5 | 8.9 ± 1.8 | 7.0 ± 1.9 | <0.001 |
| Plaque cross-sectional area (mm 2 ) | 5.8 ± 3.8 | 5.1 ± 4.1 | 4.2 ± 3.0 | 0.041 |
| Plaque burden (%) | 31.9 ± 13.4 | 33.4 ± 12.1 | 33.9 ± 13.7 | 0.7 |
| Lesion site | ||||
| Saphenous vein graft cross-sectional area (mm 2 ) | 17.0 ± 5.7 | 14.7 ± 5.7 | 11.2 ± 3.5 | <0.001 |
| Lumen cross-sectional area (mm 2 ) | 3.5 ± 1.3 | 2.9 ± 1.2 | 2.5 ± 0.9 | <0.001 |
| Plaque cross-sectional area (mm 2 ) | 13.5 ± 5.6 | 11.8 ± 5.8 | 8.7 ± 3.5 | <0.001 |
| Plaque burden (%) | 77.2 ± 9.9 | 77.8 ± 10.6 | 75.2 ± 11.7 | 0.3 |
| Lesion length (mm) | 15 ± 7 | 14 ± 6 | 14 ± 7 | 0.6 |
| Plaque morphology | 0.10 | |||
| Soft | 33 (47%) | 30 (42%) | 28 (42%) | |
| Fibrotic | 24 (34%) | 30 (42%) | 35 (52%) | |
| Calcific | 10 (14%) | 10 (14%) | 4 (6%) | |
| Mixed | 4 (6%) | 1 (1%) | 0 | |
| Remodeling index | 0.99 ± 0.15 | 1.05 ± 0.15 | 1.03 ± 0.20 | 0.14 |
| Minimum stent cross-sectional area (mm 2 ) | 6.6 ± 1.9 | 6.7 ± 1.6 | 7.0 ± 2.4 | |
| Stent expansion (%) | 60.2 ± 15.7 | 76.3 ± 15.7 | 102.9 ± 43.0 | <0.001 |
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