Stenting was initially popularized as a means of salvaging a failed balloon angioplasty procedure. However, as randomized trials demonstrated favorable outcomes with stenting, routine stent implantation became the norm. First-generation stents were bulky, difficult to deliver and not reliably adherent to their delivery catheters. Balloon predilation was accepted as necessary. However, with the advent of routine stenting, interventional cardiologists have sought ways of reducing the costs and complexity of this procedure. In this issue, Oemrawsingh et al. report their favorable experience with "direct stenting". Direct stenting is the term applied to the technique of coronary stent implantation without first preparing the way with balloon predilation. As with these authors, our experience with direct stenting has been favorable. Currently, approximately one third of stent implantations at our institution are achieved without balloon predilation.
Direct stenting may be possible, but what is the advantage? There are potential cost and time savings if balloon predilation is not required. Obviously the need for a predilation balloon and the trouble of using it is obviated. A non-randomized, case control comparison3 suggested reductions in procedure time, fluoroscopy time, radiographic contrast, balloon numbers, and procedural costs. However, such comparisons may be unreliable due to case selection. While at least one randomized study is complete (SLIDE study), results are not yet available.
Are there benefits other than cost and convenience? It is generally accepted that aggressive predilation is more likely to lead to extensive dissection than gentle predilation. By extension predilation may be more likely to lead to extensive dissection than no predilation at all. In particular, it has been suggested that direct stenting may help to "tack up" dissection flaps as they form and thereby prevent extension. Several authors have commented on what appeared to them to be relatively low rates of dissection encountered with direct stenting. Herz reported a relatively low incidence of sidebranch loss following direct stenting and speculated that this was due to a reduction in "snow plow" effect. These potential benefits remain unproven.
Balloon predilation may unnecessarily traumatize the artery, particularly if the predilation balloon does not coincide with the confines of the stent. In animal models, direct stenting appears to result in less endothelial denudation than an approach of dilation followed by stenting. This has been hypothesized to result in a reduced intimal proliferative response and potentially less restenosis and, one might speculate, less thrombotic potential.
An additional benefit to direct stenting in saphenous vein grafts has been suggested. Utilizing an emboli containment system we found less atheromatous embolic particulate debris following stent implantation than following balloon angioplasty in the setting of vein graft intervention. In particular, direct stenting was associated with less embolic debris than the combination of balloon predilation followed by secondary stenting. Although small numbers limit the conclusions that can be drawn, this does support conjecture that although dilation may disrupt friable plaque and predispose to atheroembolism, stents may play an anti-embolic role by screening and containing this particulate debris.
How often is direct stenting an option? In an early report, utilizing largely first-generation stents, direct stenting was successful in 80% of attempts. Success rates of 90-98% have subsequently been reported utilizing primarily second-generation pre-mounted stents. To date, all reports have described direct stenting only in selected patients. Briguori et al. retrospectively reviewed interventional angiograms from their institution and reported that 32% of cases would have been suitable for direct stenting. This is in accord with our current 35% rate of direct stenting. It seems reasonable to conclude that when an experienced interventionalist conservatively selects a lesion for direct stenting, he or she will most often be successful in the attempt. With additional experience and continued improvement in stenting technology it seems likely that more and more patients will be potential candidates for direct stenting.
Interestingly, the severity of the stenosis does not seem to be a reliable indicator of the likelihood of successful direct stenting. Factors which do seem to be important include guiding catheter stability, proximal tortuousity, calcification, lesion length and lesion angulation. Restenotic lesions4 and saphenous vein grafts are often easily stented directly, as they are usually smooth and free of hard, irregular atheroma. It seems that a low-profile, securely mounted stent can generally be made to cross a tight lesion if it can be made to negotiate the proximal vessel and adequate coaxial force can be applied.
Are all stents equal? Direct stenting has been reported primarily utilizing various tubular stents, particularly the NIR (Boston Scientific/Scimed, Maple Grove, Minnesota), the Multi-Link (Guidant Corporation, Santa Clara, California) and, reported in this issue of the Journal, the Jostent Flex stent (Jomed AB, Helsingborg, Sweden). Profiles of these stents range from 1.1 to 1.2 mm. Smaller experiences have been reported with the higher profile stents such as the Palmaz-Schatz (Cordis, Warren, New Jersey), MicroStent (Medtronic AVE, Minneapolis, Minnesota) and others.
Successful direct implantation of a small number of coil stents has been reported. However, adherence of coil stents to their delivery balloons may be unreliable. Self-expanding stents, such as the WallStent (Boston Scientific) and Radius stent (Boston Scientific) have also been utilized. While they have the advantage of sheaths which facilitate recovery if delivery is unsuccessful, profiles are large, limiting ease of delivery and contrast opacification when the stent is across the lesion. Once released there is the added concern that entering the unexpanded stent with a dilating balloon may be difficult.
Comparing reported success rates with various stents is hazardous due to variations in patient selection, technical and procedural factors. It seems reasonable to expect that desirable stent characteristics would include low profile, flexibility, trackability, visibility, and secure attachment to the delivery catheter.
What if direct stent delivery is attempted but unsuccessful? The reported consequences of failed direct stent delivery are few. Unreported consequences may be more common. Early reports of coronary stenting described a significant incidence of stent dislodgement on the delivery balloon and stent loss. With newer stents and delivery systems, this is less of a problem. Nevertheless, reports suggest that 4-20% of direct stenting attempts are not successful, presumably requiring removal of the stent. Fortunately, current stents can generally be successfully extracted and problems appear infrequent.
What about arterial trauma? Direct stenting may at times require more aggressive deep seating and manipulation of the guiding catheter than would have been necessary had balloon predilation been performed. However, in our experience using current guides and techniques, guide trauma has not been evident. Passing a stent through an undilated stenosis might be more traumatic than crossing with a predilation balloon. We have observed reduced flow through a tight stenosis after an unsuccessful attempt at direct stenting, although this is generally readily rectified with balloon dilation.
What about failure to expand a stent once deployed? It is rare that a stent can be successfully delivered to a stenosis, yet once there cannot be expanded. We have encountered this situation in just one patient with a presumably fibrotic stenosis following mediastinal radiation. Of greater concern is calcification, which must be considered a contraindication to direct stenting.
What other contraindications are there to direct stenting? A tight or occlusive lesion may not allow adequate opacification of the distal lesion. Balloon predilation may be necessary to allow adequate assessment of artery size, lesion length, sidebranches, and bifurcations prior to selecting and positioning a stent. Even if distal opacification is adequate at baseline, this may not be the case once a bulky stent is advanced across a tight lesion. The ability to correctly position a stent may be compromised. Obviously, this is more important if stent positioning is critical, such as when a sidebranch must be avoided.
To summarize, cost and convenience considerations argue for direct stenting in selected patients. Other advantages have been suggested but remain unproven. It seems likely that with continued technical improvements the necessity of balloon predilation will continue to decline. While predilation will continue to play a role it seems that, at least in selected patients, "direct stenting" is here to stay.
Less balloon usage
Less procedure time
Less contrast
Less radiation
Less balloon trauma outside of the stent
Less endothelial denudation
Less balloon dissection
Less ischemic time
Less cost
More guide and wire support needed
Intimal injury due to stent passage
Difficult stent retrieval, stent loss
Ischemia during difficult stent deployment
Stent selection/positioning compromised if distal
Inability to expand stent (calcification, fibrosis, balloon rupture)
Disallows potential for stand-alone balloon angioplasty
Patient selection important
More technically demanding
Tenuous guide support
Unreliable stent/delivery system
Extreme proximal tortuousity
Total occlusion
Calcified lesion
Long lesion
Bifurcation lesion
Important side-branch