Preintervention arterial remodeling affects vessel stretch and plaque extrusion during coronary stent deployment as demonstrated by three-dimensional intravascular ultrasound

Mechanism of Residual Lumen Stenosis at the Side Branch Ostium After Final Kissing Balloon Inflation: A Volumetric Intracoronary Ultrasound Study of Coronary Bifurcation Lesions

OBJECTIVES

To investigate the mechanisms of residual stenosis (RS) at side branch ostium (SBO) after final kissing balloon inflation (FKI) and clarify the impact of carina- and plaque-shifts on RS.

BACKGROUND

Carina- and plaque-shift induce SBO compromise. FKI is an effective technique to treat this complication; however, RS often persist, and are associated with restenosis at SBO.

METHODS

We performed serial volumetric analysis of 91 bifurcations in which crossover-stenting with FKI and pre-/post-intravascular ultrasounds (IVUS) were completed in both branches. The plaque- and carina-shifts were defined as an increase in the plaque-volume and a decrease in the vessel-volume at the SBO, respectively. RS at the SBO, defined as area stenosis >50% on IVUS, was identified in 19 lesions.

RESULTS

After FKI, the plaque volume- significantly increased at the SBO, with its reduction in the proximal main vessel (MV). However, at the SBO, the volumetric lumen change correlated with vessel change (ρ = 0.690, P < 0.001), but not plaque change (P = 0.390), suggesting that RS at SBO was more likely associated with inadequate vessel stretch, not plaque increase after FKI. Carina-shift was more frequently found in cases with RS, compared to those without RS (37% vs. 11%, P = 0.013). Pre-procedure IVUS findings to predict RS at SBO after FKI were negative-remodeling at distal MV, plaque -burden at distal MV, and plaque-burden at the SBO.

CONCLUSIONS

Carina-shift has a greater contribution to the formation of RS at SBO after FKI. The pre-procedure IVUS provides helpful information for predicting the RS after FKI.

Intravascular ultrasound comparison of the self-expanding Sideguard stent in the side branch versus a balloon-expandable stent in the main vessel to assess mechanisms of acute lumen gain in bifurcation lesions

OBJECTIVES

We compared the mechanisms of lumen gain after Cappella Sideguard (CS) side branch (SB) bifurcation stent deployment versus a balloon-expandable stent in the corresponding main vessel (MV).

BACKGROUND

The novel CS SB bifurcation stent is a self-expanding, thin-strut, nitinol device with anatomic flaring at the SB ostium.

METHODS

In 28 bifurcation lesions, intravascular ultrasound imaging of both the SB and the MV was performed both pre- and postintervention; vessel and lumen areas were measured every 1 mm over a 5 mm segment beginning at the carina.

RESULTS

Although minimum lumen area (MLA) within the distal 5 mm segment beginning at the carina increased from 2.8 ± 1.3 mm(2) to 3.8 ± 1.1 mm(2), P < 0.001, in the SB and from 3.4 ± 1.4 mm(2) to 6.0 ± 1.1 mm(2), P < 0.001, in the MV, stent expansion (minimum stent area/distal reference lumen area) was significantly less in the SB compared with the MV (77.8 ± 21.3% vs. 91.6 ± 18.4%, P = 0.02). Post stenting, the MLA site was located at the carina more frequently in the SB (85.7%) than in the MV (60.7%), P = 0.04. Plaque volume in the 5 mm proximal to carina in the MV tended to decrease, whereas plaque volume in the SB increased slightly with no change in overall plaque volume in the 5-mm-long segment distal to the carina in the MV, suggesting plaque shift from the proximal MV to the SB.

CONCLUSIONS

Acute CS lumen gain is less than the lumen gain of a balloon-expandable stent in the MV because of less aggressive acute expansion and/or the plaque shift from the proximal MV to the SB.

Comparative analysis of lumen enlargement mechanisms achieved with the bifurcation dedicated BiOSS) stent versus classical coronary stent implantations by means of provisional side branch stenting strategy: an intravascular ultrasound study

The aim of this study was to analyze the mechanisms of lumen enlargement in bifurcation lesions, as assessed by intravascular ultrasound (IVUS), after percutaneous treatment with classic provisional “T” stenting with conventional drug-eluting stents (DES) versus bifurcation dedicated BiOSS^® (Balton, Warsaw, Poland) stent. In this prospective study between Jan and Dec/11, 32 patients with single de novo coronary bifurcation lesions suitable for treatment with BiOSS stents were randomized (1:1). IVUS method included pre- and post-procedure analysis in the parent vessel. Vessel, lumen and plaque cross-sectional areas were determined at the target lesion [minimum lumen area (MLA) site], proximal limb, distal limb, and “window”—defined as the segment between the carina (flow divider) and the vessel wall at the level of the side branch inflow. All lesions were treated with provisional approach and only 1 case in BiOSS group had a stent implanted in the side branch. Angiographic and IVUS results including MLA at the target site and proximal/distal references were similar. However, mean window length—largest diameter within the window, was similar at baseline, but BiOSS measured significantly longer at postprocedure (2.21 ± 0.37 vs. 1.76 ± 0.52 mm, p = 0.01). In addition, the magnitude of changes in vessel (27 ± 24 % vs. 9 ± 10 %, p = 0.01) and plaque (2 ± 26 % vs. −2 ± 26 %, p = 0.02) areas at the window were significantly different for DES versus BiOSS groups, respectively. The contribution of vessel extension for lumen enlargement represented 54 versus 43 %, 130 versus 46 %, 98 versus 80 % and 51 versus 19 % of the result achieved at the proximal limb, window, distal limb and MLA sites for DES versus BiOSS, respectively; as for plaque re-distribution, results were 36 versus 57 %, −30 versus 54 %, 2 versus 20 %, and 49 versus 81 %, at the proximal limb, window, distal limb and MLA sites, respectively. These results suggest different mechanisms of lumen enlargement comparing conventional DES versus BiOSS dedicated bifurcation stent, which can impact side branch compromise during procedure.

Release of TNF-α during stent implantation into saphenous vein aortocoronary bypass grafts and its relation to plaque extrusion and restenosis

The reduction in plaque volume during stent implantation is associated with the release of particulate debris and plaque-derived soluble substances. We studied the potential release of the proinflammatory cytokine TNF-α into the coronary circulation and whether such release is related to the reduction in plaque volume and, possibly, a predictor for restenosis. In 18 male patients ( n = 24 stents) with severe stenosis in a saphenous vein aortocoronary bypass graft (SVG), we used a distal balloon occlusion-aspiration device during stent implantation. The aspirate TNF-α levels were determined before and after stent implantation and related to the angiographic and intravascular ultrasound-assessed severity of stenosis and restenosis. We found that TNF-α is, indeed, released into the aspirate of stented SVG (9 ± 1 and 28 ± 3 pg/ml before and after stent implantation, respectively, P < 0.0001) and that such release is related to the reduction in plaque volume ( r = 0.88, P < 0.0001) and associated with restenosis after 5 mo ( r = 0.71, P = 0.001). The periprocedural release of plaque-derived TNF-α possibly represents the amount and activity of the atherosclerotic process and might be a predictor for restenosis.

Intravascular ultrasound tissue harmonic imaging in vivo

Tissue harmonic imaging (THI) has been shown to increase image quality of medical ultrasound in the frequency range from 2 to 10 MHz and might, therefore, also be used to improve image quality in intravascular ultrasound (IVUS). In this study we constructed a prototype IVUS system that could operate in both fundamental frequency and second harmonic imaging modes. This system uses a conventional, continuously rotating, single-element IVUS catheter and was operated in fundamental 20 MHz, fundamental 40 MHz, and harmonic 40 MHz modes (transmit 20 MHz, receive 40 MHz). Hydrophone beam characterization measurements demonstrated the build-up of a second harmonic signal as a function of increasing pressure. Imaging experiments were conducted in both a tissue-mimicking phantom and in an atherosclerotic animal model in vivo. Acquisitions of fundamental 20 and 40 MHz and second harmonic acquisitions resulted in cross sections of the phantom and a rabbit aorta. The harmonic results of the imaging experiments showed the feasibility of intravascular THI with a conventional IVUS catheter both in a phantom and in vivo. The harmonic acquisitions also showed the potential of THI to reduce image artifacts compared to fundamental imaging.

Plaque development, vessel curvature, and wall shear stress in coronary arteries assessed by X-ray angiography and intravascular ultrasound

The relationships among vascular geometry, hemodynamics, and plaque development in the coronary arteries are complex and not yet well understood. This paper reports a methodology for the quantitative analysis of in vivo coronary morphology and hemodynamics, with particular emphasis placed on the critical issues of image segmentation and the automated classification of disease severity. We were motivated by the observation that plaque more often developed at the inner curvature of a vessel, presumably due to the relatively lower wall shear stress at these locations. The presented studies are based on our validated methodology for the three-dimensional fusion of intravascular ultrasound (IVUS) and X-ray angiography, introducing a novel approach for IVUS segmentation that incorporates a robust, knowledge-based cost function and a fully optimal, three-dimensional segmentation algorithm. Our first study shows that circumferential plaque distribution depends on local vessel curvature in the majority of vessels. The second study analyzes the correlation between plaque distribution and wall shear stress in a set of 48 in vivo vessel segments. The results were conclusive for both studies, with a stronger correlation of circumferential plaque thickness with local curvature than with wall shear stress. The inverse relationship between local wall shear stress and plaque thickness was significantly more pronounced (p<0.025) in vessel cross sections exhibiting compensatory enlargement (positive remodeling) without luminal narrowing than when the full spectrum of disease severity was considered. The inverse relationship was no longer observed in vessels where less than 35% of vessel cross sections remained without luminal narrowing. The findings of this study confirm, in vivo, the hypothesis that relatively lower wall shear stress is associated with early plaque development.

Reduction of stent artifacts using high-frequency harmonic ultrasound imaging

Tissue harmonic imaging (THI) has been shown to improve medical ultrasound (US) image quality in the frequency range from 2 to 10 MHz and might, therefore, also be advantageous in high-frequency US applications, like US biomicroscopy and intravascular US (IVUS). In this study, we compared high-frequency THI (40 MHz) with fundamental imaging (20 and 40 MHz) with a distorting reflective metal stent in the near fields of both a spherically-focused US biomicroscopy transducer (aperture 8 mm, focal distance 13 mm) and an unfocused elliptical IVUS element. Hydrophone measurements of the harmonic beam (40 MHz) of both transducers showed relatively low signal strength in the near field compared with both (20 and 40 MHz) fundamental beams. For the focused transducer, THI suppressed the second stent echo up to 14 dB compared with fundamental imaging. No significant reduction in stent artifact imaging was observed for the unfocused IVUS element.

In vivovalidation of a novel semi-automated method for border detection in intravascular ultrasound images

The aim of this work was to evaluate a new semi-automated intravascular ultrasound (IVUS) border detection method. The method was used to identify the lumen and the external elastic membrane or the borders of stents in 80 IVUS images, randomly selected from 10 consecutive human coronary arteries. These semi-automated results were compared with observations of two experts. Several indices in each case were obtained in order fully to evaluate the method. The time required for identification of the borders was also recorded. The interobserver variability of the method ranged from 1.21% to 5.61%, the correlation coefficient from 0.98 to 0.99, the slope was close to unity (0.94-1.03), the y intercept close to zero and the Williams index value was close to unity (range 0.67-0.91). The time (mean+/-SD) required for the method to identify the borders of the different vessel layers for the whole IVUS sequence was 5.2+/-0.2 min. The results demonstrate that the method is reliable and capable of identifying rapidly and accurately the different vessel layers depicted in IVUS images.