Use and Benefits of IVUS
Abstracts & Commentary
Synopsis: Selective IVUS use to optimize coronary interventional procedures might result in improved outcomes without increased procedure time, resource use, or large increases in cost.
Sources: Choi J, et al. Am Heart J. 2001;142:112-118; Moussa I, et al. Am J Cardiol. 2001;88:294-296.
Choi and colleagues sought to determine whether the routine use of intravascular ultrasound (IVUS) to optimize stent implantation improved acute and long-term clinical outcomes, and whether such an approach involved more resource use while remaining cost-effective. They analyzed 278 consecutive patients; 178 patients received IVUS and 100 patients had angiographically guided stent implantation. All IVUS imaging was performed at the discretion of the primary operator with the goal of optimizing angiographically guided stent deployment with the angiographic criteria of full stent apposition to the vessel wall, adequate stent symmetry, and acute gain of > 0.80. Assessment of resource use included procedure time, fluoroscopy time, contrast volume, and other equipment used (such as catheters, balloons, stents, and guidewires), as well as overall procedure cost. Clinical outcomes included in-hospital abrupt closure and 6-month major adverse cardiac events (MACE) including cardiac death, myocardial infarction (MI), or target vessel revascularization (TVR).
There were no differences in total procedure time, fluoroscopy time, or contrast use between the groups. While 47% of patients undergoing postimplantation IVUS underwent additional procedures to optimize results, this did not result in increased use of equipment, with the exception of the IVUS catheter itself. Total procedure costs were higher in the IVUS group ($4142 ± 1547 vs $3635 ± 1949, P = 0.03), a difference largely attributable to the cost of the IVUS catheter ($575 at this institution). The abrupt closure rate was lower in the patients receiving IVUS guidance (0.6% vs 4%, P = 0.04). In addition, there was a trend toward lower 6-month MACE in patients undergoing IVUS (11% vs 19%, P = 0.08).
Choi et al concluded that while procedural costs were somewhat higher in the IVUS-guided group, these costs would be offset somewhat by lower rates of abrupt closure and a trend toward lower rates of MACE at 6 months in the IVUS-treated group. They acknowledge that this study was limited by the nonrandomized use of IVUS guidance (which may have resulted in a higher proportion of "difficult" lesions in the IVUS-guided group) and by a sample size that may have been insufficient to detect a difference in clinical outcomes between the groups at 6 months.
Moussa and colleagues postulated that IVUS would provide the most benefit for patients in whom IVUS data would be inconsistent with coronary angiography. Of particular interest were those patients in whom angiography resulted in underestimation of vessel diameter. In these cases, IVUS data might allow the interventional operator to choose a strategy that might result in a larger minimal lumen diameter at the end of the procedure, which may in turn translate into lower rates of subsequent restenosis. Therefore, Moussa et al sought to determine the clinical and angiographic characteristics that correlated with a discrepancy between IVUS and quantitative coronary angiography (QCA) measurements, thereby defining a population of patients most likely to receive real clinical benefit in undergoing preintervention evaluation by IVUS.
Moussa et al identified 334 patients who underwent high-quality IVUS evaluation prior to coronary intervention. Baseline measurements obtained included minimal luminal cross-sectional area (CSA), reference vessel diameter, and vessel diameter at the lesion site. QCA was performed by an experienced angiographer blinded to the IVUS results. The discrepancy between the IVUS and QCA measurements of vessel diameter at the site of the lesion was calculated. In vessels where there was a large difference (= 1 mm) between the IVUS and QCA images, Moussa et al attribute the discrepancy to 2 factors: diffuse coronary atherosclerosis affecting the reference vessel and, more commonly, compensatory vessel enlargement at the lesion site ("the Glagov effect"). Either of these pathoanatomic features would be underestimated by angiographic "luminology" and more accurately assessed using IVUS. Logistic regression and multivariate analysis of clinical and angiographic characteristics were performed to identify predictors of a difference between measurements obtained by the 2 modalities. Independent predictors of discrepancy between IVUS and QCA assessment were 1) small angiographic reference vessel diameter (< 3 mm); 2) lesion location in a proximal segment of the coronary tree; and 3) presence of diabetes.
Moussa et al suggest that these findings might allow the operator to identify patients who would be most likely to benefit from IVUS imaging. By obtaining a more accurate (and often times larger) estimation of vessel size, an optimal interventional strategy, ideally resulting in larger postprocedural minimal luminal CSA, would be facilitated.
Comment by Sarah M. Vernon, MD
Since the earliest published studies in coronary stenting revealed that larger vessel diameter and stented luminal CSA are associated with lower rates of restenosis and target vessel revascularization, "bigger is better" has become the interventional cardiologist’s mantra. Early IVUS studies also revealed high rates of incomplete stent expansion, which could be minimized with high-pressure balloon inflation after deployment. With contemporary stent design and implantation techniques, the potential role of IVUS guidance in optimizing clinical outcomes needed to be redefined. While there is little doubt that IVUS guidance can prove invaluable in performing coronary intervention, it is important that the information obtained translates into improved patient outcomes to justify the additional time and expense of this procedure. Data from the CRUISE study, a large, randomized trial published in August 2000, suggest that optimizing stent implantation with IVUS guidance resulted in larger minimal lumen diameter and larger minimal stent area, both measures that have been shown to correlate with lower restenosis rates.1 More importantly, patients randomized to IVUS guided stent implantation in CRUISE experienced improved clinical outcomes, with lower TVR at 9 months of follow-up (8.5% vs 15.3%, P < 0.05).
Choi et al demonstrate that, in their series of patients, while the cost of performing IVUS-optimized stent implantation was somewhat higher (the cost of the IVUS catheter itself), IVUS was not associated with longer procedure times or increased use of other resources. In addition, the procedural cost of performing IVUS was offset by the costs associated with lower abrupt closure rates and a trend toward lower TVR rates in patients receiving IVUS guided stenting. However, this study was not randomized and may have lacked an adequate sample size to detect a significant difference in clinical outcomes as reported in CRUISE. In addition, their strategy of post-deployment IVUS-guided optimization of stenting may not reflect the utility of preintervention IVUS guided lesion assessment to assist with device selection.
The brief report from Moussa et al, while also somewhat limited by small sample size, helps to clarify subsets of patients (those with smaller vessels, proximal lesion location, or diabetes) in whom preprocedural IVUS evaluation might provide significant benefit by providing a more accurate assessment of vessel size. This, in turn, might significantly alter procedural strategy and device selection (most notably selection of larger stents) that might allow the operator to achieve a larger MLD at the end of the procedure. While previously published data would suggest that it is likely that this would translate into improved clinical outcomes, namely lower restenosis rates, this was not demonstrated in this study. Nonetheless, the simple clinical and angiographic criteria outlined by these studies could be used to reserve pre-intervention IVUS imaging for the patients most likely to derive clinical benefit from it. Such a "selective" approach to IVUS-guided stent deployment might also prove to be the most cost effective. Taken together, these 2 studies suggest that selective IVUS use to optimize coronary interventional procedures might result in improved outcomes without increased procedure time, resource use, or large increases in cost.
Reference
1. Fitzgerald P, et al. Circulation. 2000;102:523-530.
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