Initial Clinical Experience Using an Ostial Stent Positioning System (Ostial Pro‚Ñ¢) for the Accurate Placement of Stents in the

From Borgess Heart Institute, Kalamazoo, Michigan; §Heart & Vascular Adventist Midwest Health, Lagrange, Illinois; †Baptist Hospital, Knoxville, Tennessee; √Weill Cornell Medical College, New York Hospital, New York, New York; *Columbia Presbyterian Hospital, New York, New York. Disclosures: Supported in part by a grant from Ostial Solutions, LLC. TAF is a cofounder and shareholder in Ostial Solutions, LLC. FS and MF are shareholders in Ostial Solutions, LLC. Manuscript submitted October 28, 2008, provisional acceptance given December 2, 2008, final version accepted December 16, 2008. Address for correspondence: Tim A. Fischell, MD, FACC, Professor of Medicine, Michigan State University; Borgess Heart Institute 1521 Gull Road, Kalamazoo, MI 49048. E-mail: tafisc@gmail.com

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ABSTRACT: Objective. To evaluate the safety and efficacy of a new nitinol stent positioning system to assist in the placement of aorto-ostial coronary stents. Background. The stenting of aorto-ostial lesions is technically challenging. Methods. We report the first clinical series using the Ostial Pro™ to assist in the precise placement of stents in coronary aorto-ostial lesions. These results were compared to matched cases performed without the ostial positioning system. Results. The Ostial Pro is a simple nitinol device with self-expanding legs that are advanced just distal to the tip of the guiding catheter. The nitinol legs prevent the entry of the guiding catheter into the target vessel and align the tip of the guiding catheter. Using the Ostial Pro positioning device, angiographic and clinical success was achieved in 30/30 (100%) cases. Excellent stent positioning was confirmed by angiography (n = 30) and intravascular ultrasound (n = 28). The final true ostial dimension was larger than the stented segment minimum luminal diameter in 30/30 cases. In a matched consecutive cohort of 30 consecutive coronary aorto-ostial stent cases placed without the Ostial Pro, we observed an ostial stent malpositioning in 18/30 (60%) of cases (p Conclusions. 1) The Ostial Pro is a new FDA-cleared nitinol device that is simple to use and effective in allowing the precise placement of stent(s) at the aorto-ostial location; 2) this approach appears to provide an efficient means to assure accurate stent placement and minimal residual stenosis in these difficult-to-treat lesions.

J INVASIVE CARDIOL 2009;21:53–59

Key words: aorto-ostial, stenosis, stent placement, restenosis, nitinol

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The precise positioning of stents to treat an aorto-ostial lesion is difficult using conventional angiographic landmarks.^1–7 Because of these technical difficulties with stent placement, several investigators have studied alternative treatments for aorto-ostial lesions, but with relatively poor long-term outcomes.^5,7–11 The failure to precisely place the stent at, or just proximal to, the true ostium may lead to adverse outcomes. If the stent is placed just distal to the lesion, there is a high incidence of restenosis.^1,5–7 If a second stent placement is required, this will add to the cost and time of the intervention and potentially increases risks, such as early or late stent thrombosis due to significant stent overlap. If one errs on the side of placing the stent proximally, this will often prevent reengagement of a guiding catheter. This may make it difficult or impossible to treat the vessel with percutaneous intervention for restenosis or disease progression at a later date.^5,12,13 The Ostial Pro™ (Ostial Solutions, LLC, Kalamazoo, Michigan) 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 to prevent the entry of the guiding catheter into the target vessel, mark the plane of the aortic wall and align the tip of the guide with the aorto-ostial plane (Figures 1 and 2). We report the first clinical series of the successful use of this new tool for the precise placement of stents in the aorto-ostial location in 30 consecutively treated patients.

Methods

Between July 2007 and February 2008, 30 consecutive patients with clinically significant aorto-ostial coronary lesions were treated using the Ostial Pro stent positioning device. The lesions treated were in the right coronary artery (RCA) (n = 17), saphenous vein grafts (SVG) (n = 7), the left main coronary artery (n = 4), a free radial artery graft (n = 1), and an anomalous left anterior descending coronary artery (LAD) arising as a separate ostium from the aorta (n = 1). Five experienced operators at 5 cardiovascular centers performed the interventions. All treated cases were included for analysis. No patients were excluded from enrollment related to any anatomical considerations, and there were no exclusions for any “run-in” or “learning-curve” cases. The data presented are obtained from the first 30 Ostial Pro coronary cases performed in the world. Thirty cases were performed using the Ostial Pro without any preselection criteria (i.e., all-comers) (Figures 1–3). The Ostial Pro was back-loaded (n = 27) or front-loaded (n = 3) into a 6 Fr (n = 27) or a 7 Fr (n = 3) guiding catheter. The guiding catheter was advanced to the ascending aorta using a 0.035 inch J guidewire. The guiding catheters were flushed and then engaged to the target vessel ostium. Coronary angiography was performed in at least one projection to demonstrate the target aorto-ostial lesion, with minimal foreshortening. After engaging the target vessel, the aorto-ostial lesion was crossed with a 0.014 inch coronary guidewire. Predilatation was performed in 9 patients and direct stenting was performed in 21 patients. In all cases, the balloons and the stent delivery systems were passed through the Ostial Pro stent positioning device as it was “parked” inside the distal portion of the coronary guiding catheter. There was no discernible resistance to passage of the balloons or the stent delivery systems (up to 4.5 mm stent delivery system [SDS]) in any case. After the stent was advanced to a position 1–3 cm distal to the ostial lesion, the guiding catheter was withdrawn ~3–4 mm proximal to the ostium of the target vessel. The position in the ascending aorta and proximal to the ostium was confirmed by contrast injection. Coaxial alignment of the guiding catheter tip to the ostium was maintained during this disengagement from the target vessel by stabilization of the guiding catheter over the SDS maintained in a position distal to the target vessel ostium. While holding the stent and coronary guidewire in place, the Ostial Pro was advanced inside the guiding catheter, over the SDS, until the nitinol “legs” and gold-plated “feet” popped out, and were fully expanded outside the tip of the guiding catheter, just proximal to the target vessel ostium. The guiding catheter was then slightly advanced until the feet and legs of the Ostial Pro were visibly flattened and engaged to the aortic wall, and the guiding catheter tip was just outside the target vessel ostium (Figures 1A, 2C and 3C). When the Ostial Pro is thus positioned, the guiding catheter tip is held relatively coaxial to, and just proximal to the ostium, but cannot enter the target vessel (Figures 1A and 2C). The stent delivery balloon is then withdrawn and aligned such that the SDS proximal marker band is just distal to the guide tip, with the proximal edge of the stent itself aligned just proximal to the gold feet of the Ostial Pro (Figure 3D). The correct positioning of the stent using this tool does not require an angiographic view to line up “parallel” to the struts. The key methodology for using this tool to achieve correct positioning involves engaging the legs to the aortic wall and then using the tip of the guiding catheter as the primary landmark for SDS alignment. When the legs are engaged to the aortic wall and the guide catheter tip sits just behind the plane of the legs, the guide catheter tip is essentially always 0.5–0.7 mm proximal to the true ostium. The proximal marker of the SDS then needs to be aligned just at the distal tip of the guiding catheter, regardless of the appearance of the legs/feet. Confirmation of the guide tip alignment just outside the ostium is done with contrast injection and the stent is deployed at high pressure (Figure 1B) using the guiding catheter tip as the primary landmark. Typically, the Ostial Pro stent positioning device is removed from the guiding catheter after the initial stent deployment. In all of our cases, at least one additional high-pressure “flaring” balloon inflation was performed in a more proximal position, with at least 3–4 mm of the deployment balloon sitting proximal to the true ostium (Figure 1C). Intravascular ultrasound (IVUS) using the Galaxy system (Boston Scientific Corp., Natick, Massachusetts) (n = 25) or the Volcano system (Volcano Corp., Rancho Cordova, California) (n = 3) was performed in 28/30 cases to confirm and measure the precision of the stent position relative to the ostium. A comparable age and lesion-matched historical control group (Table 1) was collected using screening from the BMC squared data set (Blue Cross-Blue Shield Cardiac Consortium of Michigan) from Borgess Medical Center. Using this tool, we identified 30 consecutive aorto-ostial coronary stent cases performed immediately prior to the availability of the Ostial Pro. These 30 cases included 19 RCA cases, 5 left main lesions, 1 anomalous LAD arising from the aorta, 1 left internal mammary artery graft, and 4 saphenous vein graft cases performed by 5 experienced interventional cardiologists. There was a careful independent review of these cases by 2 experienced interventional cardiologists. All operative reports and films were reviewed. Data was collected to document the accuracy of stent placement. Stents placed > 1 mm proximal or distal to the true ostium was considered a “miss”. Cases were also evaluated relative to the ability to reengage the target ostium. Cases in which the vessel could not be reengaged due to proximal stent protrusion into the aorta were classified as a proximal miss. Cases in which there was a need for a second stent placement due to distal positioning was classified as a distal miss. Procedural outcomes. Procedural success was defined as an uncomplicated procedure (no stent thrombosis, no dissection, no device failure or complication related to use of the Ostial Pro) with successful stent placement (Intravascular ultrasound. A blinded IVUS reader reviewed both the short- and long-axis IVUS images. The reviewer used a caliper-based technique from the long-axis IVUS images to measure the deviation of the proximal stent edge from the true aorto-ostial plane (in millimeters). 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 (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 Results 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 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).

Discussion

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 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.

Conclusions

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.

References

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