Analysis of coronary bifurcations by intravascular ultrasound and virtual histology

Multicentre, randomized comparison of two-stent and provisional stenting techniques in patients with complex coronary bifurcation lesions: the DEFINITION II trial

AIM

The present study aimed to assess the benefits of two-stent techniques for patients with DEFINITION criteria-defined complex coronary bifurcation lesions.

METHODS AND RESULTS

In total, 653 patients with complex bifurcation lesions at 49 international centres were randomly assigned to undergo the systematic two-stent technique (two-stent group) or provisional stenting (provisional group). The primary endpoint was the composite of target lesion failure (TLF) at the 1-year follow-up, including cardiac death, target vessel myocardial infarction (TVMI), and clinically driven target lesion revascularization (TLR). The safety endpoint was definite or probable stent thrombosis. At the 1-year follow-up, TLF occurred in 37 (11.4%) and 20 (6.1%) patients in the provisional and two-stent groups, respectively [77.8%: double-kissing crush; hazard ratio (HR) 0.52, 95% confidence interval (CI) 0.30-0.90; P = 0.019], largely driven by increased TVMI (7.1%, HR 0.43, 95% CI 0.20-0.90; P = 0.025) and clinically driven TLR (5.5%, HR 0.43, 95% CI 0.19-1.00; P = 0.049) in the provisional group. At the 1 year after indexed procedures, the incidence of cardiac death was 2.5% in the provisional group, non-significant to 2.1% in the two-stent group (HR 0.86, 95% CI 0.31-2.37; P = 0.772).

CONCLUSION

For DEFINITION criteria-defined complex coronary bifurcation lesions, the systematic two-stent approach was associated with a significant improvement in clinical outcomes compared with the provisional stenting approach. Further study is urgently warranted to identify the mechanisms contributing to the increased rate of TVMI after provisional stenting.

STUDY REGISTRATION

http://www.clinicaltrials.com; Identifier: NCT02284750.

Optical coherence tomography predictors of target vessel myocardial infarction after provisional stenting in patients with coronary bifurcation disease

BACKGROUND

Provisional side branch (SB) stenting is correlated with target vessel myocardial infarction (TVMI) in patients with coronary bifurcation lesions. However, the mechanisms underlying this association remain unknown.

OBJECTIVES

To determine the correlation between SB lesion length with vulnerable plaques and TVMI using optical coherence tomography (OCT).

BACKGROUND

The correlation between SB lesion length with vulnerable plaques and TVMI is unknown.

METHODS

A total of 405 patients with 405 bifurcation lesions who underwent preprocedure OCT imaging of both the main vessel (MV) and the SB were enrolled. Patients were divided into long SB lesion (SB lesion length ≥10 mm) and short SB lesion (SB lesion length <10 mm) groups according to quantitative coronary analysis; they were also stratified by the presence of vulnerable plaques identified by OCT. The primary endpoint was the occurrence of TVMI after provisional stenting at 1-year follow-up.

RESULTS

In total, 178 (43.9%) patients had long SB lesions. Vulnerable plaques were predominantly localized in the MV and were more frequently in the long SB lesion group (42.7%) than in the short SB lesion group (24.2%, p < .001). At 1-year follow-up after provisional stenting, there were 31 (7.7%) TVMIs, with 21 (11.8%) in the long SB lesion group and 10 (4.4%) in the short SB lesion group (p = .009). Multivariate regression analysis showed that long SB lesion length (p = .011), absence of vulnerable plaques in the polygon of confluence (p = .001), and true coronary bifurcation lesions (p = .004) were the three independent factors of TVMI.

CONCLUSIONS

The presence of long SB lesion with MV vulnerable plaques predicts the increased risk of TVMI after provisional stenting in patients with true coronary bifurcation lesions. Further studies are warranted to identify the best stenting techniques for coronary bifurcation lesions with long SB lesions.

Effect of stenosis eccentricity on the functionality of coronary bifurcation lesions-a numerical study

Interventional cardiologists still rely heavily on angiography for the evaluation of coronary lesion severity, despite its poor correlation with the presence of ischemia. In order to improve the accuracy of the current diagnostic procedures, an understanding of the relative influence of geometric characteristics on the induction of ischemia is required. This idea is especially important for coronary bifurcation lesions (CBLs), whose treatment is complex and is associated with high rates of peri- and post-procedural clinical events. Overall, it is unclear which geometric and morphological parameters of CBLs influence the onset of ischemia. More specifically, the effect of stenosis eccentricity is unknown. Computational fluid dynamic simulations, under a geometric multiscale framework, were executed for seven CBL configurations within the left main coronary artery bifurcation. Both concentric and eccentric stenosis profiles of mild to severe constriction were considered. By using a geometric multiscale framework, the fractional flow reserve, which is the gold-standard clinical diagnostic index, could be calculated and was compared between the eccentric and concentric profiles for each case. The results suggested that for configurations where the supplying vessel is stenosed, eccentricity could have a notable effect on and therefore be an important factor that influences configuration functionality.

Contrast Layering

Patients with angiographically normal coronary arteries sometimes exhibit delayed clearance of contrast medium. This contrast layering (CL) was tested with intravascular ultrasound (IVUS) and markers of endothelial dysfunction and oxidative stress. The study group (n = 26) consisted of patients with CL and the control group (n = 32) comprised patients with normal coronary arteries despite angina symptoms. The CL was observed in 36 coronary arteries of 26 patients in the study group. Total antioxidant status and nitric oxide levels were significantly lower; total oxidant status, malondialdehyde plasma levels, and oxidative stress index were significantly higher in patients with CL than in controls. The IVUS studies revealed that atherosclerotic plaque burden, fibrous tissue, dense calcific tissue, and necrotic core ratios were significantly higher in the coronary segments with CL compared with adjacent normal segments. These results support the concept of CL as a new angiographic appearance of early atherosclerosis.

Comparison of lipid deposition at coronary bifurcations versus at nonbifurcation portions of coronary arteries as determined by near-infrared spectroscopy

Atherosclerosis has been shown to develop preferentially at sites of coronary bifurcation, yet culprit lesions resulting in ST-elevation myocardial infarction do not occur more frequently at these sites. We hypothesized that these findings can be explained by similarities in intracoronary lipid and that lipid and lipid core plaque would be found with similar frequency in coronary bifurcation and nonbifurcation segments. One hundred seventy bifurcations were identified, 156 of which had comparative nonbifurcation segments proximal and/or distal to the bifurcation. We compared lipid deposition at bifurcation and nonbifurcation segments in coronary arteries using near-infrared spectroscopy (NIRS), a novel method for the in vivo detection of coronary lipid. Any NIRS signal for the presence of lipid was found with similar frequency in bifurcation and nonbifurcation segments (79% vs 74%, p = NS). Lipid core burden index, a measure of total lipid quantity indexed to segment length, was similar across bifurcation segments as well as their proximal and distal controls (lipid core burden index 66.3 ± 106, 67.1 ± 116, and 66.6 ± 104, p = NS). Lipid core plaque, identified as a high-intensity focal NIRS signal, was found in 21% of bifurcation segments, and 20% of distal nonbifurcation segments (p = NS). In conclusion, coronary bifurcations do not appear to have higher levels of intracoronary lipid or lipid core plaque than their comparative nonbifurcation regions.

Ultrasound-assessed non-culprit and culprit coronary vessels differ by age and gender

AIM: To investigate age- and gender-related differences in non-culprit versus culprit coronary vessels assessed with virtual histology intravascular ultrasound (VH-IVUS).

METHODS: In 390 patients referred for coronary angiography to a single center (Luzerner Kantonsspital, Switzerland) between May 2007 and January 2011, 691 proximal vessel segments in left anterior descending, circumflex and/or right coronary arteries were imaged by VH-IVUS. Plaque burden and plaque composition (fibrous, fibro-fatty, necrotic core and dense calcium volumes) were analyzed in 3 age tertiles, according to gender and separated for vessels containing non-culprit or culprit lesions. To classify as vessel containing a culprit lesion, the patient had to present with an acute coronary syndrome, and the VH-IVUS had to be performed in a vessel segment containing the culprit lesion according to conventional coronary angiography.

RESULTS: In non-culprit vessels the plaque burden increased significantly with aging (in men from 37% ± 12% in the lowest to 46% ± 10% in the highest age tertile, P < 0.001; in women from 30% ± 9% to 40% ± 11%, P < 0.001); men had higher plaque burden than women at any age (P < 0.001 for each of the 3 age tertiles). In culprit vessels of the lowest age tertile, plaque burden was significantly higher than that in non-culprit vessels (in men 48% ± 6%, P < 0.001 as compared to non-culprit vessels; in women 44% ± 18%, P = 0.004 as compared to non-culprit vessels). Plaque burden of culprit vessels did not significantly change during aging (plaque burden in men of the highest age tertile 51% ± 9%, P = 0.523 as compared to lowest age tertile; in women of the highest age tertile 49% ± 8%, P = 0.449 as compared to lowest age tertile). In men, plaque morphology of culprit vessels became increasingly rupture-prone during aging (increasing percentages of necrotic core and dense calcium), whereas plaque morphology in non-culprit vessels was less rupture-prone and remained constant during aging. In women, necrotic core in non-culprit vessels was very low at young age, but increased during aging resulting in a plaque morphology that was very similar to men. Plaque morphology in culprit vessels of young women and men was similar.

CONCLUSION: This study provides evidence that age- and gender-related differences in plaque burden and plaque composition significantly depend on whether the vessel contained a non-culprit or culprit lesion.

Associations of reactive hyperemia index and intravascular ultrasound-assessed coronary plaque morphology in patients with coronary artery disease

Although reactive hyperemia index (RHI) predicts future coronary events, associations with intravascular ultrasound (IVUS)-assessed coronary plaque structure have not been reported. This study therefore investigated associations between RHI and IVUS-assessed coronary plaques. In 362 patients RHI was measured by noninvasive peripheral arterial tonometry and coronary plaque components (fibrous, fibrofatty, necrotic core, and dense calcium) were identified by IVUS in 594 vessel segments of the left anterior descending, circumflex, and/or right coronary arteries. RHI values <1.67 were considered abnormal. Analysis of variance was used to detect independent associations between RHI and plaque composition. Patients with an abnormal RHI had greater plaque burden (41% vs 39% in patients with normal RHI, p = 0.047). Compared to patients with normal RHI, plaque of patients with abnormal RHI had more necrotic core (21% vs 17%, p <0.001) and dense calcium (19% vs 15%, p <0.001) and less fibrous (49% vs 54%, p <0.001) and fibrofatty (11% vs 14%, p = 0.002) tissue. After adjustment for age, gender, cardiovascular risk factors, and drug therapy, abnormal RHI remained significantly associated with fibrous (F ratio 14.79, p <0.001), fibrofatty (F ratio 5.66, p = 0.018), necrotic core (F ratio 14.47, p <0.001), and dense calcium (F ratio 10.80, p = 0.001) volumes. In conclusion, coronary artery plaques of patients with abnormal RHI had a larger proportion of necrotic core and dense calcium. The association of an abnormal RHI with a plaque structure that is more prone to rupture may explain why these patients exhibit a greater risk of coronary events.

Deviation from Murray's law is associated with a higher degree of calcification in coronary bifurcations

OBJECTIVE

Murray's law describes the optimal branching anatomy of vascular bifurcations. If Murray's law is obeyed, shear stress is constant over the bifurcation. Associations between Murray's law and intravascular ultrasound (IVUS) assessed plaque composition near coronary bifurcations have not been investigated previously.

METHODS

In 253 patients plaque components (fibrous, fibro-fatty, necrotic core, and dense calcium) were identified by IVUS in segments proximal and distal to the bifurcation of a coronary side branch. The ratio of mother to daughter vessels was calculated according to Murray's law (Murray ratio) with a high Murray ratio indicating low shear stress. Analysis of variance was used to detect independent associations of Murray ratio and plaque composition.

RESULTS

Patients with a high Murray ratio exhibited a higher relative amount of dense calcium and a lower amount of fibrous and fibro-fatty tissue than those with a low Murray ratio. After adjustment for age, sex, cardiovascular risk factors or concomitant medications, the Murray ratio remained significantly associated with fibrous volume distal (F-ratio 4.90, P=0.028) to the bifurcation, fibro-fatty volume distal (F-ratio 4.76, P=0.030) to the bifurcation, and dense calcium volume proximal (F-ratio 5.93, P=0.016) and distal (F-ratio 5.16, P=0.024) to the bifurcation.

CONCLUSION

This study shows that deviation from Murray's law is associated with a high degree of calcification near coronary bifurcations. Individual deviations from Murray's law may explain why some patients are prone to plaque formation near vessel bifurcations.

Flow and atherosclerosis in coronary bifurcations

Coronary bifurcations are among the most frequent sites affected by atherosclerosis. In these regions, complex haemodynamic conditions prevail and local flow disturbances dictate the localisation and progression of atheroma. Endothelial shear stress (ESS) is the main flow-related factor affecting the distribution of atherosclerosis in a bifurcation. Plaques are more prevalent in low ESS areas, such as the lateral walls of the main vessel and side branches, while they are less common in the flow divider or carina, which is characterised by high ESS. However, the carina is not free of atheroma and is affected in up to one third of cases, but never in isolation. Lesions in the carina are likely to develop at a later stage of atherosclerosis, as result of circumferential expansion of plaques from the lateral wall. Pulsatile flow augments the local atherogenic environment by inducing low and oscillatory ESS. The geometrical configuration is also important as increased curvature and wide angles between the side branches of the bifurcation intensify flow perturbations, and highly curved segments show low ESS in the inner aspect of curvatures. Further research on the flow conditions which determine the initiation and progression of atherosclerosis in bifurcations will allow for more efficient prevention and management strategies.