Final results of the STent versus directional coronary Atherectomy Randomized Trial (START)

One-year outcomes of patients undergoing percutaneous coronary intervention with the revived directional coronary atherectomy catheter: Insights from the J-PCI OUTCOME registry

OBJECTIVES

We sought to investigate the 1-year outcomes, including all-cause and cardiovascular mortality, major adverse cardiovascular events (MACEs), and major bleeding, of patients undergoing percutaneous coronary intervention (PCI) with or without the revived directional coronary atherectomy (DCA) catheter in a Japanese nationwide registry.

BACKGROUND

Clinical data regarding the midterm outcomes of patients undergoing PCI with DCA are scarce in contemporary real-world practice.

METHODS

We analyzed the data of 74,764 patients who underwent PCI at 179 hospitals from January 2017 to December 2018. The baseline characteristics and 1-year outcomes of patients with stable coronary artery disease or unstable angina who underwent PCI with or without DCA were assessed.

RESULTS

Overall, 431 patients (0.6%) underwent PCI with DCA. Patients in the DCA group were younger and predominantly male, with fewer comorbidities than patients in the non-DCA group. Stentless PCI with DCA following additional drug-coated balloon (DCB) angioplasty was the dominant strategy in the DCA group (43.6%). One-year outcomes, including all-cause mortality (1.2% in the DCA group vs. 2.5% in the non-DCA group, respectively, p = 0.075), cardiovascular death (0.9% vs. 1.0%, p = 0.69), MACEs (1.9% vs. 1.8%, p = 0.96), and nonfatal major bleeding requiring readmission (1.2% vs. 1.4%, p = 0.62), were comparable between the two groups. In the DCA group, 1-year outcomes were comparable, regardless of whether the stent or DCB was used.

CONCLUSIONS

One-year clinical outcomes after PCI with DCA in patients with stable coronary artery disease or unstable angina are acceptable, regardless of stent use.

Impact of directional coronary atherectomy followed by drug-coated balloon strategy to avoid the complex stenting for bifurcation lesions

Although the simple single stenting rather than complex double stenting is recommended on percutaneous coronary intervention (PCI) for bifurcation lesions, double stenting cannot always be avoided. We investigated the impact of directional coronary atherectomy (DCA), followed by drug-coated balloon (DCB) treatment to reduce the number of stents and avoid complex stenting in PCI for bifurcation lesions and short-term patency. DCA treatment without stents was attempted for 27 bifurcation lesions in 25 patients, of those, 26 bifurcation lesions in 24 patients were successfully treated and 3-month follow-up angiography and optical coherence tomography (OCT) were performed. Sixteen lesions (59.3%) were related to left main trunk distal bifurcations, and 7 (25.9%) were true bifurcation lesions. Among the true bifurcation lesions, 4 lesions (57.1%) needed 1 stent, and the other 3 lesions (42.9%) needed no stents. Among the non-true bifurcation lesions, 1 lesion (5.0%) needed bailout stent and other lesions (95.0%) needed no stents. According to DCA followed by DCB treatment, the angiographic mean diameter stenosis improved from 65.5 ± 15.0% to 7.8 ± 9.8%, and the mean plaque area in intravascular ultrasound improved from 80.4 ± 10.5% to 39.0 ± 11.5%, respectively. Angiographic and OCT late lumen loss values were 0.2 ± 0.6 mm and 1.4 ± 1.9 mm, respectively. No patient had in-hospital major adverse cardiac events (MACE) and 3-month MACE. In conclusion, compared with standard provisional side branch stenting strategy, DCA followed by DCB treatment might reduce the number of stents, avoid complex stenting for major bifurcation lesions and provide good short-term outcomes.

Clinical expert consensus document on quantitative coronary angiography from the Japanese Association of Cardiovascular Intervention and Therapeutics

Quantitative coronary angiography (QCA) remains to play an important role in clinical trials and post-marketing surveillance related to the safety and efficacy of new PCI devices. In this document, the current standard methodology of QCA is summarized. In addition, its history, recent development and future perspectives are also reviewed.

Stentless treatment strategy for left circumflex artery ostial stenosis: Directional coronary atherectomy followed by drug-eluting balloon

A 60-year-old man with history of exertional angina pectoris was referred for treatment of an ostial left circumflex (LCX) coronary artery stenosis. The branch angle between left anterior descending artery (LAD) and LCX was shallow, therefore stent implantation seemed at risk of "carina shift" of plaque to the LAD ostium as well as higher in-stent restenosis. Therefore, directional coronary atherectomy (DCA, Atherocut™, L-size, NIPRO, Osaka, Japan) was performed at the ostium of the LCX lesion. After evaluating plaque accumulation using intravascular ultrasound (IVUS), DCA was circumferentially performed 16 times, from 2 atm to 3 atm, using an 8 fr guide system. Although angiogram and IVUS showed excellent results, adjunctive balloon dilatation with 3.5 mm paclitaxel-coated balloon was performed to prevent restenosis. At 8 months, the patient reported being angina-free, and subsequent follow-up angiogram showed no restenosis of LCX. Paclitaxel-coated balloon following DCA for LCX ostial stenosis seems to be safe and effective for both acute and chronic results, suggesting a potential stentless therapeutic option. <Learning objective: Directional coronary atherectomy in combination with drug-eluting balloon may be a potential stentless therapeutic option, especially for the ostial stenosis of left circumflex artery.>.

Current techniques for MR imaging of atherosclerosis

Vessel wall imaging of large vessels has the potential to identify culprit atherosclerotic plaques that lead to cardiovascular events. Comprehensive assessment of atherosclerotic plaque size, composition, and biological activity is possible with magnetic resonance imaging (MRI). Magnetic resonance imaging of the atherosclerotic plaque has demonstrated high accuracy and measurement reproducibility for plaque size. The accuracy of in vivo multicontrast MRI for identification of plaque composition has been validated against histological findings. Magnetic resonance imaging markers of plaque biological activity such as neovasculature and inflammation have been demonstrated. In contrast to other plaque imaging modalities, MRI can be used to study multiple vascular beds noninvasively over time. In this review, we compare the status of in vivo plaque imaging by MRI to competing imaging modalities. Recent MR technological improvements allow fast, accurate, and reproducible plaque imaging. An overview of current MRI techniques required for carotid plaque imaging including hardware, specialized pulse sequences, and processing algorithms are presented. In addition, the application of these techniques to coronary, aortic, and peripheral vascular beds is reviewed.

Directional coronary atherectomy: a time for reflection. Should we let it go?

A series of interventional tools have emerged since the advent of percutaneous coronary angioplasty. Several are fundamental and used routinely, while others less favourable have fallen short of mainstream therapy and/or have settled as a niche device. We present an overview of the evolution of directional coronary atherectomy (DCA), a unique device that was originally conceived in 1984 to solve the limitations of balloon angioplasty. Unfortunately, we have witnessed its use fall significantly out of favour due to premature and controversial study results. In many interventional laboratories DCA is no longer available. However, we strongly feel that allowing DCA to join the list of extinct interventional tools would be very unfortunate. We, herein, present a series of complex percutaneous coronary procedures to illustrate the convenience of DCA use as a lesion-specific niche device. Finally, DCA offers a valuable distinct clinical research function as it allows for in vivo pathological coronary tissue examination. In conclusion, we plead for its continued production and use as an interventional niche device for the wellbeing of our patients.

Randomized comparison of debulking followed by stenting versus stenting alone for ostial left anterior descending artery stenosis: intravascular ultrasound guidance

BACKGROUND

Although directional coronary atherectomy (DCA) before stenting has the advantage of combining substantial removal of atheromatous plaque and prevention of elastic recoil, there has been no randomized study to investigate its efficacy in ostial left anterior descending artery (LAD) lesions. This study was aimed to evaluate the effect of DCA followed by stenting on ostial LAD stenosis under the guidance of intravascular ultrasound (IVUS).

METHODS

Eighty-six patients with ostial LAD stenoses were randomly assigned to DCA followed by stenting (group I) or stenting alone (group II). Aggressive DCA or optimal stenting was performed in both groups under the guidance of IVUS. The primary end point was angiographic restenosis at 6 months.

RESULTS

Baseline clinical and angiographic characteristics were similar between the 2 groups. The postprocedural minimal lumen diameter was larger in group I than group II (4.0 +/- 0.4 mm vs. 3.5 +/- 0.5 mm, P <.001). However, the angiographic restenosis rates were not significantly different between the 2 groups (9/32 [28.1%] in group I vs. 11/30 [36.7%] in group II, P =.472). The postprocedural IVUS stent area was the only independent determinant of restenosis by multivariate analysis (odds ratio.61, 95% CI 0.41-0.92, P =.018).

CONCLUSIONS

DCA followed by stenting achieved greater lumen gain than stenting alone for ostial LAD stenosis. However, DCA did not improve angiographic restenosis.

Routine intravascular ultrasound guidance of percutaneous coronary intervention

Intravascular ultrasound (IVUS) has played an integral role in the evolution of interventional cardiology. However, routine IVUS guidance of coronary stent implantation is not supported by a critical reappraisal of the available evidence. Although there is a trend toward a benefit with respect to target lumen revascularization favoring IVUS-guided coronary stent implantation, it is likely that this effect is driven by improved outcomes in small vessels, long coronary stenoses, and possibly saphenous vein graft interventions. No consistent trend in the incidence of death or myocardial infarction is apparent. Furthermore, the safety, efficacy, and effectiveness of IVUS should be taken into account when considering the goals, risks, benefits, and alternatives to such a treatment strategy.

Quantitative angiographic and intravascular ultrasound study >5 years after directional coronary atherectomy

Aggressive and optimal directional coronary atherectomy (DCA) using intravascular ultrasound (IVUS) guidance provides favorable outcomes within 1 year. However, no previous data are available on the changes that occur in target lesions for the long term after stand-alone DCA. This study's aim evaluates, using quantitative angiography and intravascular ultrasonography, the natural history of changes that occur in target lesions between short- (about 6 months) and long-term (>5 years) follow-up angiography after stand-alone DCA. Of 186 patients (221 lesions) with successful stand-alone DCA, 48 patients (53 lesions) underwent revascularization within 6 months, and 14 patients subsequently died, leaving a study population of 124 patients (154 lesions). Complete quantitative coronary angiography (QCA) was obtained in 91 patients (101 lesions) and complete serial IVUS assessment was obtained for 38 lesions before and after intervention and during follow-up. From short- to long-term follow-up angiography, the minimal luminal diameter significantly increased (from 2.12 to 2.56 mm; p <0.0001); lesion subgroups with >30% diameter stenosis at short-term follow-up angiography showed significant late regression as assessed by QCA. Serial IVUS assessment revealed that the vessel cross-sectional area did not change (from 17.3 to 17.4 mm(2); p = NS); however the lumen cross-sectional area significantly increased (from 7.3 to 9.5 mm(2); p <0.0001) due to the reduction of plaque plus media cross-sectional area (from 10.0 to 7.9 mm(2); p <0.0001). The change in lumen cross-sectional area correlated with the change in plaque plus media cross-sectional area (r = -0.686, p <0.0001). Target lesions show late regression due to plaque reduction at >5 years after stand-alone DCA.

Effect of preintervention remodeling type on subsequent coronary artery behavior after directional atherectomy

To evaluate the influence of preintervention remodeling on subsequent vessel behavior after directional coronary atherectomy (DCA) under intravascular ultrasound (IVUS) guidance, serial (before and after DCA and at 6-month follow-up) IVUS data were analyzed for 246 lesions that were classified into 2 categories: positive remodeling (PR) in 77 lesions versus intermediate or negative remodeling in 169 lesions. Although the 2 groups had similar baseline characteristics, IVUS data showed that the PR group had a greater acute lumen area (LA) gain without an increased late LA loss, resulting in a greater net (acute plus late) LA gain and follow-up LA. This suggests that IVUS-guided DCA may neutralize the negative impact of preintervention PR on late vessel patency.

Intravascular ultrasound-guided directional coronary atherectomy for unprotected left main coronary stenoses with distal bifurcation involvement

Stent implantation in unprotected left main coronary artery (LMCA) bifurcation lesions may improve procedural and late clinical outcomes. However, concerns regarding stent-related complications, such as stent jail, subacute thrombosis, and in-stent restenosis remain. Optimal debulking by directional coronary atherectomy (DCA) with intravascular ultrasound (IVUS) guidance may be effective in this complex lesion subset, but this strategy has not yet been established. Our objective was to evaluate the safety and efficacy of IVUS-guided DCA for unprotected LMCA stenoses with distal bifurcation involvement. A total of 67 consecutive patients were included in this study and procedural success was achieved in all cases. Two cardiac deaths (2.9%) were noted and 3 patients (4.5%) underwent repeat angioplasty during hospitalization. There was no Q-wave myocardial infarction or emergency bypass surgery. Non-Q-wave myocardial infarction (creatine kinase-MB >3 times normal) occurred in 13.4% of patients. Stent implantation was necessary in 17 cases (25.4%) to achieve an optimal result. IVUS showed an improved lumen cross-sectional area and a low plaque burden in the LMCA after intervention. All-cause mortality, angiographic restenosis, and the target lesion revascularization rates at 6 months were 7.4%, 23.8%, and 20.0%, respectively. With IVUS guidance, aggressive DCA can be performed safely in unprotected LMCA bifurcation lesions, and optimal angiographic and IVUS results can be achieved with low residual plaque burden, which leads to a low restenosis rate. Optimal lesion debulking by DCA does not necessarily need adjunctive stenting in this specific anatomic subset.

Evolving Strategies for the Prevention and Treatment of Coronary Restenosis

Percutaneous coronary intervention has become an increasingly attractive alternative to medical therapy and surgical revascularization for the treatment of coronary artery disease. Over 1.5 million interventional procedures are performed annually worldwide, with the rate of procedures performed continuing to rise dramatically. Restenosis following percutaneous coronary intervention occurs at rates of 20% to 40% and has remained the Achilles heel of the procedure. Numerous early attempts at the prevention of restenosis with oral pharmacologic agents, such as antithrombotic therapies, lipid lowering agents, vasodilators, and growth factor inhibitors, failed to show benefit in clinical trials. The introduction of intracoronary stents resulted in a 30% reduction in restenosis rates by abolishing the early vessel recoil following angioplasty. However, as more complex lesions underwent percutaneous coronary intervention with stenting, rates of “in-stent” restenosis remained high (20% to 30%). With technologic advances and greater understanding of vascular pathobiology, novel therapeutic strategies, such as local delivery of ionizing radiation, immunosuppressive agents, and gene therapy, have been deployed to prevent coronary restenosis. In addition, a number of mechanical and radiation-based strategies have been used to treat those patients who develop restenosis. This review considers these emerging strategies for the prevention and treatment of restenosis.

Effect of plaque debulking before stent implantation on in-stent neointimal proliferation: a serial 3-dimensional intravascular ultrasound study

BACKGROUND

Recent intravascular ultrasound (IVUS) studies have suggested that plaque burden has a role in promoting intimal hyperplasia after stenting. We report on volumetric assessments of in-stent neointimal formation with 3-dimensional IVUS analysis, comparing directional coronary atherectomy (DCA) plus stenting (DCA/stenting) to stenting without DCA.

METHODS

Twenty-four patients (24 lesions) treated with DCA before stenting were matched to 24 patients (24 lesions) receiving stenting without DCA. All stents were a single Multilink stent. In both groups, serial IVUS was performed before and after intervention and during the 6-month follow-up period. The arterial segments that were analyzed with a computer-based contour detection program were the same as the stented segments analyzed on serial studies. These measurements were obtained: (1) lumen volume (LV), (2) stent volume (SV), (3) vessel volume (VV), (4) in-stent neointimal volume (ISV) calculated as SV-LV, and (5) percent in-stent neointimal volume (%ISV) calculated as ([SV-LV]/SV) x 100.

RESULTS

Baseline characteristics of the 2 groups were similar. After intervention, both groups achieved similar LV (140.0 mm(3) DCA/stenting vs 135.2 mm(3) stenting alone). However, the follow-up ISV and %ISV were significantly smaller in the DCA/stenting group (19.6 +/- 12.2 mm(3) DCA/stenting vs 44.6 +/- 29.5 mm(3) stenting alone; P =.00040; 15.3% +/- 10.6% DCA/stenting vs 31.5% +/- 17.7% stenting alone; P =.00040). Consequently, the DCA/stenting group showed a significantly greater follow-up LV (121.0 +/- 51.5 mm(3) DCA/stenting vs 91.5 +/- 26.7 mm(3) stenting alone; P =.016).

CONCLUSIONS

Plaque removal with DCA before stenting inhibits in-stent neointimal hyperplasia.

Drug-eluting stents: potential applications for peripheral arterial occlusive disease

Many different approaches have been evaluated to prevent restenosis in stents after vascular implantation. Currently, drug-eluting stents are extremely promising in suppressing neointimal hyperplasia. Various animal studies and randomized trials in humans have shown excellent results in terms of safety and efficacy during intermediate-term follow-up. This article will give an overview of experimental and clinical data of the different agents in published and ongoing trials.

Predictors of vessel remodeling following directional coronary atherectomy

The purpose of this study was to clarify predictors of vessel remodeling following directional coronary atherectomy (DCA). Negative remodeling after DCA leads to restenosis. However, little is known about the predictors of the vessel remodeling. Serial IVUS was performed in 43 lesions. The vessel remodeling was defined as adaptive if vessel area at follow-up minus postprocedure vessel area was > 0 mm2, or as constrictive if < 0 mm2. Adaptive remodeling occurred in 21 (49%) lesions. Postprocedure percent plaque area was smaller in the adaptive group (32.9% +/- 5.7% vs. 45.5% +/- 8.8%; P < 0.005). At follow-up, vessel area was larger in the adaptive group. However, plaque area was similar between the two groups. As a result, lumen area was larger in the adaptive group. Multivariate analyses showed that postprocedure percent plaque area < 40% was the only predictor of adaptive remodeling (odds ratio, 6.68; P < 0.05).

Debulking and stenting versus debulking only of coronary artery disease in patients treated with cilostazol (final results of ESPRIT)

Stenting inhibits vascular constrictive remodeling after directional coronary atherectomy (DCA). Cilostazol has been reported to control neointimal proliferation after stenting. This study's aim was to examine the effect of debulking and stenting with antirestenotic medication on restenosis. After optimal DCA, 117 lesions were randomly assigned to either the DCA with stent (DCA-stent) (58 lesions) group or the DCA only (59 lesions) group. Multilink stents were implanted in the DCA-stent group. Cilostazol (200 mg/day) without aspirin was administered to both groups for 6 months. Ticlopidine (200 mg/day) was given to the DCA-stent group for 1 month. Serial quantitative angiography and intravascular ultrasound (IVUS) were performed at the time of the procedure and at 6-month follow-up. The primary end point was 6-month angiographic restenosis. Clinical event rates at 1 year were also assessed. Baseline characteristics were similar. All procedures were successful. No adverse effects to cilostazol were observed. Postprocedural lumen diameter was significantly larger (3.27 vs 2.92 mm; p <0.0001) in the DCA-stent group. However, the follow-up lumen diameter was not significantly different (2.53 vs 2.41 mm, DCA-stent vs DCA). IVUS revealed that intimal proliferation was significantly larger in the DCA-stent group (4.2 vs 1.5 mm(2); p <0.0001), which accounted for the similar follow-up lumen area (6.5 vs 7.1 mm(2)). The restenosis rate was low in both groups (5.4% vs 8.9%), and the difference was not significant. Clinical event rates at 1 year were also not significantly different. These results suggest that optimal lesion debulking by DCA does not always need adjunctive stenting if cilostazol is administered.

Mechanisms of acute gain and late lumen loss after atherectomy in different preintervention arterial remodeling patterns

The main mechanism of restenosis after directional coronary atherectomy (DCA) remains obscure. We investigated mechanisms of restenosis after DCA in different coronary artery remodeling patterns. DCA was performed in 51 de novo lesions. The lesions were evaluated by intravascular ultrasound (IVUS) before, immediately after, and 6 months after the procedure. According to the IVUS findings before DCA, we classified the lesions into the following 3 groups: (1) positive (n = 10), (2) intermediate (n = 25), and (3) negative (n = 16) remodeling. We measured lumen area, vessel area, and plaque area using IVUS before DCA, immediately after DCA, and at follow-up. Lumen area increase after DCA was mainly due to plaque area reduction in the positive and intermediate remodeling groups (90 plus minus 15% and 80 plus minus 25% increase in lumen area, respectively), whereas that in the negative remodeling group was due to both plaque area reduction (57 plus minus 22% increase in lumen area) and vessel area enlargement (43 plus minus 33% increase in lumen area). The plaque area increase correlated strongly with late lumen area loss in the positive and intermediate remodeling groups (r = 0.884, p <0.001; r = 0.626, p <0.001, respectively), but the decrease in vessel area was not correlated with lumen area loss. In contrast, both an increase in plaque area and a decrease in vessel area were correlated with late lumen area loss (r = 0.632, p = 0.009; r = 0.515, p = 0.041) in the negative remodeling group. Coronary artery restenosis after atherectomy was primarily due to an increase in plaque in the positive and/or intermediate remodeling groups. However, in the negative remodeling group, late lumen loss might have been caused by both an increase in plaque and vessel shrinkage.

Elective stenting of unprotected left main coronary artery stenosis: effect of debulking before stenting and intravascular ultrasound guidance

OBJECTIVES

We sought to evaluate: 1) the long-term outcomes of 127 selected patients receiving unprotected left main coronary artery (LMCA) stenting; and 2) the impact of the debulking procedure before stenting and intravascular ultrasound (IVUS) guidance on their clinical outcomes.

BACKGROUND

The long-term safety of stenting of unprotected LMCA stenoses has not been established yet.

METHODS

A total of 127 consecutive patients with unprotected LMCA stenosis and normal left ventricular function were treated by elective stenting. The long-term outcomes were evaluated between two groups: IVUS guidance (n = 77) vs. angiographic guidance (n = 50); and debulking plus stenting (debulking/stenting; n = 40) vs. stenting only (n = 87).

RESULTS

Angiographic restenosis was documented in 19 (19%) of 100 patients. The lumen diameter after stenting was significantly larger in IVUS-guided group (p = 0.003). The angiographic restenosis rate was significantly lower in the debulking/stenting group (8.3% vs. 25%, p = 0.034). The reference artery size was the only independent predictor of angiographic restenosis. During follow-up (25.5 +/- 16.7 months), there were four deaths, but no nonfatal myocardial infarctions occurred. The survival rate was 97.0 +/- 1.7% at two years.

CONCLUSIONS

These data suggest that stenting of unprotected LMCA stenosis might be associated with a favorable long-term outcome in selected patients. Guidance with IVUS may optimize the immediate results, and debulking before stenting seems to be effective in reducing the restenosis rate. However, we need a large-scale, randomized study.

Directional coronary atherectomy: the Vienna experience

BACKGROUND

Several multicenter trials have shown excellent results for directional coronary atherectomy (DCA) in a selected patient cohort. To prove the applicability of this method in daily clinical routine and a nonselected patient cohort, we analyzed 46 consecutive cases performed at our catheterization lab.

METHODS

DCA was performed as a routine procedure in 45 suitable patients. Balloon dilatation or stent implantation postprocedure was accomplished only in case of unsatisfactory results. Quantitative coronary angiography was achieved pre- and postprocedure as well as at 6-month follow-up.

RESULTS

Optimal atherectomy < 20% residual stenosis was reached in 24 (52%) of 46 target lesions and a residual stenosis < 50% in 46 (100%) lesions. Procedure-related complications occurred in three (6%) patients (one major complication, death, < 24 hours, 2%; two minor complications, pseudoaneurysm, 4%). The 6-month angiographic follow-up revealed a binary restenosis rate of 29% (n = 11). Ten out of 11 restenotic lesions required revascularization. When patients were stratified in two groups according to their preprocedural minimal lumen diameter (MLD), this parameter proved to be a very strong predictor of outcome. The percentage of restenosis was significantly higher in patients with an MLD > 1.60 mm compared to patients with a smaller MLD (54% vs 19.3%; P < 0.0001). Reference vessel diameter preprocedure did not differ significantly.

CONCLUSIONS

Our study demonstrated that DCA is a suitable technique for the daily clinical routine, as the rates of complications and restenosis were similar to that in a highly selective patient cohort. Additionally, our study showed that patient selection should include preprocedural analysis of MLD in order to achieve optimal results. Therefore, atherectomy yielded comparable results to other conventional techniques and may be used instead of or in combination with them.

Intravascular ultrasound: novel pathophysiological insights and current clinical applications

Intravascular ultrasound (IVUS) is a valuable adjunct to angiography, providing new insights in the diagnosis of and therapy for coronary disease. Angiography depicts only a 2D silhouette of the lumen, whereas IVUS allows tomographic assessment of lumen area, plaque size, distribution, and composition. The safety of IVUS is well documented, and the assessment of luminal dimensions represents an important application of this modality. Comparative studies show the greatest disparities between angiography and ultrasound after mechanical interventions. In young subjects, normal intimal thickness is typically approximately 0.15 mm. With IVUS, lipid-laden lesions appear hypoechoic, fibromuscular lesions generate low-intensity echoes, and fibrous or calcified tissues are echogenic. Calcium obscures the underlying wall (acoustic shadowing). The extent and severity of disease by angiography and ultrasound are frequently discrepant. Arterial remodeling refers to changes in vascular dimensions during the development of atherosclerosis. At diseased sites, the external elastic membrane may actually shrink in size, contributing to luminal stenosis. The interpretation of IVUS relies on simple visual inspection of acoustic reflections to determine plaque composition. However, different tissue components may look quite similar, and artifacts may adversely affect ultrasound images. IVUS commonly detects occult disease in angiographically "normal" sites. In ambiguous lesions, ultrasound permits lesion quantification, particularly for left main coronary disease. IVUS has emerged as the optimal method for the detection of transplant vasculopathy. An important potential application of ultrasound is the identification of atheromas at risk of rupture. The mechanisms of action of interventional devices have been elucidated using IVUS, and ultrasound is used by some operators to select the most suitable interventional device. IVUS-derived residual plaque burden is the most useful predictor of clinical outcome. In restenosis after balloon angioplasty, negative remodeling is a major mechanism of late lumen loss. IVUS is not routinely used for stent optimization, and there is no consensus regarding optimal procedural end points. Ultrasound has proven useful in evaluating brachytherapy. New and emerging applications for IVUS are continuing to evolve, particularly in atherosclerosis regression-progression trials.