Initial Clinical Experience Using an Ostial Stent Positioning System (Ostial Pro™) for the Accurate Placement of Stents in the
- Volume 21 - Issue 2 - February, 2009
- Posted on: 2/10/09
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Quantitative coronary angiography (QCA). QCA was performed for all 30 Ostial Pro cases by trained core lab technicians. Angiograms from the stent implantation procedure at the time of intervention were recorded in digital format for offline analysis by QCA. All angiograms were analyzed using the CMS Medis QCA software program, version 6.0.41 (Medis Medical Imaging Systems, B.V., Leiden, The Netherlands) on angiographic workstations per facility standard operating procedures and the CMS Medis QCA system.
The following parameters were measured prior to deployment of the device (baseline): minimum luminal diameter (MLD) within the target segment; (interpolated) reference vessel diameter (RVD) obtained 5–10 mm distal to the target segment; lesion length; percent diameter stenosis (%DS); and lumen diameter at the true ostium of the target vessel. The following parameters were measured upon completion of the stent deployment: MLD within the stented segment; (interpolated) RVD obtained 5–10 mm distal to the stented region; %DS; and lumen diameter at the true ostium of the treated vessel. The true ostium is defined as the opening of the target vessel at the aortic wall. The %DS was calculated by CMS Medis software using the definition: [1-(MLD/RVD)] x 100. Two experienced interventional cardiologists assessed the accuracy of stent positioning by reviewing the operative reports and the angiograms for each of the 30 consecutive historical “control” cases as well as the 30 Ostial Pro cases. Visual estimates of lesion severity, lesion calcification, and so forth were used to compare the historical control patient lesions and the Ostial Pro cohort (Table 1).
All cases in both the control and the Ostial Pro groups were assessed regarding stent placements with cases categorized as: 1) too distal (> 1 mm distal to the angiographically determined ostium with > 30% residual stenosis); 2) too proximal (> 1 mm proximal to the angiographically determined ostium, particularly if the ostium could not be reengaged with guiding or diagnostic catheter(s); or 3) correctly positioned (< 1 mm from the true ostium without the need for a second stent and with the ability to reengage the ostium).
Statistics. The QCA dimensions prior to and after stenting were compared using Excel spreadsheets (Microsoft Corp., Bellevue, Washington). This software was used to calculate %DS pre- and post-stenting and the true ostial diameter at the completion of the procedure. The statistical package from Excel was used for statistical comparisons. The comparison of the final minimal stented segment dimension and the final RVD was compared to the final true ostial dimension using ANOVA for repeated measures. Fisher’s exact testing was used to compare the “miss” rate using the Ostial Pro versus the historical control cases. All data are reported as mean ± SE. A p-value < 0.05 was considered statistically significant.
Successful stent placement with excellent stent positioning was achieved in 30/30 (100%) of the cases using the Ostial Pro device. In no case were the operators unable to reengage the target vessel, and in no case was the stent placed distally enough to warrant placement of a second stent for a distal “miss.” The mean distance of the proximal stent edge from the true ostium, as measured from long-axis IVUS (n = 28) was + 0.1 ± 0.1 mm (i.e., 0.1 mm into the aorta). The placement positions ranged from -0.2 mm (i.e., 0.2 mm distal to ostium to +0.5 mm (i.e., 0.5 mm proximal to ostium). In 28/28 (100%) IVUS cases, the stent was judged to be essentially flush at the ostial plane (i.e., within 0.5 mm of the true ostium).
QCA demonstrated the unexpected result that we have called “conical flaring” of the proximal edge of the stent (Figure 3B and angiographic and IVUS images in Figures 4 and 5). We have defined this as a finding that the stent is flared at the true ostium, such that the proximal edge of the stent has a diameter that is > 10% larger than the MLD of the stented segment. This result was observed in 23/30 (77%) cases, as measured by QCA. This may be related to the positioning of struts at the true ostium followed by a high-pressure “flaring” balloon inflation. Anecdotally, this is a relatively uncommon angiographic appearance when aorto-ostial stents are placed without the Ostial Pro stent positioning system.
The historical control patients had poor stent positioning outcomes, with significant “geographic misses” in 18/30 cases (p < 0.0001 vs. Ostial Pro series). In 14/18 “misses” (78% of “misses”), the stents were placed too distally. Nine of these distal “misses” were treated with balloon angioplasty and 5 cases were treated with the placement of a second overlapping stent. In 2 of these 5 cases, the ostium was missed again after the second stent placement (both missed proximally with the inability to reengage the ostium). In 4/18 “misses” (22%), the stents were placed too proximally. In all 4 of theses cases, the vessel could not be reengaged with a guiding catheter and/or diagnostic catheter after the proximal “miss” due to stent protrusion into the aorta.
It is important to note that the 5 operators who performed the procedures in the 30 control cases had a combined interventional cardiology experience of > 19,000 interventions and a mean career experience of 15.8 years. These were highly experienced operators with slightly greater total (career) experience compared to the operators performing the treatment (Ostial Pro) cases (mean experience 14.3 years, > 17,000 career cases).
The accurate positioning of stents to treat aorto-ostial lesions in the native coronary circulation, renal arteries and saphenous vein grafts is technically challenging. Coronary aorto-ostial lesions represent a relatively small minority of stent cases, with an estimated incidence of 5–7%. However, this still represents a rather significant number of stent procedures (estimated 70–80,000 coronary aorto-ostial cases/year worldwide).
Several techniques using conventional coronary guidewires have been described to assist with accurate stent positioning with modest success.11,12 These techniques, however, are not particularly precise and have not been widely adopted. The interest in developing devices to assist in correct placement of stents in the aorto-ostial location has grown in the last few years. At least two start-up medical device companies are in the process of developing and testing stent delivery systems intended to assist in aorto-ostial stenting. However, the Ostial Pro represents the first FDA-cleared device designed to assist in the precise placement of stents at the aorto-ostial location.
The Ostial Pro is a relatively simple nitinol device that is positioned within the guiding catheter. It has distal self-expanding legs that are advanced just distal to the tip of the guiding catheter after the ostial lesion has been crossed with the coronary guidewire and stent delivery system. The expanded nitinol legs with gold-plated “feet” prevent the entry of the guiding catheter into the target vessel, mark the plane of the aortic wall, and align and stabilize the tip of the guide just proximal to the aorto-ostial plane.
The Ostial Pro does reduce the effective inner diameter of a guiding catheter by ~0.012 inch. Because of the slit in the nitinol cylinder of the Ostial Pro, the same device is compatible with 6 Fr, 7 Fr and 8 Fr guiding catheters. The device allows placement of up to 4.5 mm diameter coronary stents using a 6 Fr guiding catheter, and up to a 6.0 mm peripheral stent in a 7 Fr guiding catheter (e.g., for renal artery use). For larger stents (e.g., 7.0 mm diameter peripheral stents), use of the Ostial Pro would require an 8 Fr guiding catheter.
In this case series, we report the successful and precise placement of stents in 30 consecutive patients with coronary aorto-ostial lesions. After correct stent placement using the Ostial Pro, it was clear that the usual angiographic landmarks used to evaluate the location of the ostium were often misleading. Excellent stent positioning was confirmed by IVUS in 28/28 cases and by angiography in 30/30 cases. There were no cases requiring a second stent placement due to the (historically) common error of placing the stent too distal to the true ostial lesion. In no case did the stent protrude so proximally into the aorta that one could not reengage the coronary ostium.
There were no device failures, malfunctions or device-related complications using the Ostial Pro stent positioning device. The final angiographic results were excellent, with a mean final %DS of -1%, and a mean dimension at the true ostium that was 29% larger, on average, than either the MLD of the stented segment or the RVD. It also appears that the use of this device was associated with decreased procedural time and radiation exposure and a lower volume of radiographic contrast use.
Importantly, the results using the Ostial Pro were markedly superior to the results observed in a contemporary and well-matched historical control group. Compared to the Ostial Pro group, which had accurate stent placement in 30/30 cases without any issues related to reengagement or a need for a second stent placement, the control group had significant stent misplacement observed in 60% (18/30) of cases (p < 0.0001 versus Ostial Pro results).
Study limitations. This was a carefully conducted consecutive case-control trial. This type of study design has inherent limitations that could be related to bias in case selection, operator experience, and so forth. As shown, however in the comparison of the two cohorts, there do not appear to be any significant differences between the cohorts with regard to lesion types or operator experience. The use of IVUS in the treatment (Ostial Pro) group may actually bias the data against this group since IVUS is presumably a more sensitive tool than angiography for detecting stent misplacement.
The Ostial Pro is a new nitinol device that appears effective in allowing the precise placement of stents at the aorto-ostial location. This approach appears to provide a simple and efficient means to assure accurate stent placement and minimal residual stenosis in these difficult-to-treat lesions. Further studies will be required to determine the clinical and/or economic impact of precise stent positioning using this device.