Remodeling Index Compared to Actual Vascular Remodeling in Atherosclerotic Left Main Coronary Arteries as Assessed With Long-Term (≥12 Months) Serial Intravascular Ultrasound

Clinical factors associated with slow flow in left main coronary artery-acute coronary syndrome without cardiogenic shock

Since slow flow can be a fatal complication in left main coronary artery (LMCA)-acute coronary syndrome (ACS) patients, it should be important to anticipate and prepare slow flow during primary PCI for LMCA-ACS. We hypothesized that intravascular ultrasound (IVUS) findings would be useful to predict slow flow for LMCA-ACS patients without cardiogenic shock (CS). The purpose of this study was to investigate clinical factors associated with slow flow in LMCA-ACS patients without CS. We included 60 LMCA-ACS patients without CS, and divided into the slow flow group (n = 18) and the non-slow flow group (n = 42). Slow flow was defined as either transient or persistent TIMI flow grade ≤ 2. The prevalence of ST-segment elevation myocardial infarction (STEMI) was significantly higher in the slow flow group (55.6%) than in the non-slow flow group (11.9%) (p = 0.002). In the IVUS analysis, remodeling index was significantly greater in the slow flow group (1.15 ± 0.17) than in the non-slow flow group (0.99 ± 0.11) (p = 0.001). The multivariate logistic regression analyses in the IVUS factors revealed that remodeling index was significantly associated with slow flow (0.1 increase: OR 2.238, 95% CI 1.144-4.379, p = 0.019). In conclusion, remodeling index was significantly associated with slow flow. Our results suggest that the remodeling index determined by IVUS would be useful to find high-risk features of slow flow in LMCA-ACS patients without CS.

Relationship between arterial remodelling and serial changes in coronary atherosclerosis by intravascular ultrasound: an analysis of the IBIS-4 study

AIMS

Arterial remodelling is an important determinant of coronary atherosclerosis. Assessment of the remodelling index, comparing a lesion to a local reference site, is a suboptimal correlate of serial vascular changes. We assessed a novel approach which, unlike the local-reference approach, uses the entire artery's global remodelling as reference.

METHODS AND RESULTS

Serial (baseline and 13 months) intravascular ultrasound was performed in 146 non-infarct-related arteries of 82 patients treated with high-intensity statin. Arteries were divided into 3-mm segments (n = 1479), and focal remodelling was characterized in individual segments at both timepoints applying the global arterial reference approach. First, we compared preceding vascular changes in relation to follow-up remodelling. Second, we examined whether baseline remodelling predicts subsequent plaque progression/regression. At follow-up, segments with constrictive vs. compensatory or expansive remodelling had greater preceding reduction of vessel area (-0.67 vs. -0.38 vs. -0.002 mm2; P < 0.001) and lumen area (-0.82 vs. -0.09 vs. 0.40 mm2; P < 0.001). Overall, we found significant regression in percent atheroma volume (PAV) [-0.80% (-1.41 to -0.19)]. Segments with constrictive remodelling at baseline had greater subsequent PAV regression vs. modest regression in the compensatory, and PAV progression in the expansive remodelling group (-6.14% vs. -0.71% vs. 2.26%; P < 0.001). Lesion-level analyses (n = 118) showed no differences when remodelling was defined by the local reference approach at baseline or follow-up.

CONCLUSION

Remodelling assessment using a global arterial reference approach, but not the commonly used, local reference site approach, correlated reasonably well with serial changes in arterial dimensions and identified arterial segments with subsequent PAV progression despite intensive statin treatment and overall atheroma regression.

Association of slow flow with clinical factors in intravascular ultrasound-guided percutaneous coronary intervention for patients with left main trunk-acute myocardial infarction

BACKGROUND

Slow flow can be fatal in primary percutaneous coronary interventions for left main trunk (LMT)-acute myocardial infarction (AMI), however, risk factors for slow flow in LMT-AMI have not been well investigated. Intravascular ultrasound (IVUS) may help to stratify the high-risk lesion for slow flow in LMT-AMI.

METHODS

A total of 51 LMT-AMI were included as the study population, and were divided into the slow-flow group (n=22) and the non-slow-flow group (n=29). Slow flow was defined as either transient or persistent Thrombolysis in Myocardial Infarction (TIMI) flow grade ≤2.

RESULTS

The incidence of in-hospital death was higher in the slow-flow group (27.3%) than the non-slow-flow group (10.3%) without reaching statistical significance (p=0.116). Although the reference diameter measured by angiography was not different between the two groups, the vessel diameter measured by IVUS was significantly longer in the slow-flow group (5.22±0.69mm) than in the non-slow-flow group (4.50±0.47mm) (p<0.001). Multivariate logistic regression analyses revealed that the vessel diameter by IVUS (OR 27.487, 95%CI 3.975-190.062, p=0.001) and the vessel area by IVUS (OR 1.458, 95%CI 1.160-1.832, p=0.001) were significantly associated with slow flow.

CONCLUSIONS

In LMT-AMI, the vessel diameter measured by IVUS was closely associated with slow flow, while the reference diameter measured by angiography was not associated with slow flow. IVUS would be important to find high-risk features for slow flow in LMT-AMI.

The effect of negative remodeling on fractional flow reserve after cardiac transplantation

BACKGROUND

Negative remodeling is a common occurrence early after cardiac transplantation. Its impact on the development of myocardial ischemia is not well documented. The aim of this study is to investigate the impact of negative remodeling on fractional flow reserve after cardiac transplantation.

METHODS

Thirty-four cardiac transplant recipients underwent intravascular ultrasound (IVUS) and fractional flow reserve (FFR) assessment soon after transplantation and one year later. Patients were divided into those with and without negative remodeling based on IVUS, and the impact on FFR was assessed. In the 19 patients with negative remodeling, there was no significant change in plaque volume (119.3±82.0 to 131.3±91.2mm³, p=0.21), but vessel volume (775.6±212.0 to 621.9±144.1mm³, p<0.0001) and lumen volume (656.3±169.1 to 490.7±132.0mm³, p<0.0001) decreased significantly and FFR likewise decreased significantly (0.88±0.06 to 0.84±0.07, p=0.04). In the 15 patients without negative remodeling, vessel volume did not change (711.7±217.6 to 745.7±198.5, p=0.28), but there was a significant increase in plaque volume (126.8±88.3 to 194.4±92.7, p<0.001) and a resultant significant decrease in FFR (0.89±0.05 to 0.85±0.05, p=0.01).

CONCLUSION

Negative remodeling itself, without any change in plaque volume can cause a significant decrease in fractional flow reserve after cardiac transplantation and appears to be another possible mechanism for myocardial ischemia.

A Novel Algorithm to Quantify Coronary Remodeling Using Inferred Normal Dimensions

Background

Vascular remodeling, the dynamic dimensional change in face of stress, can assume different directions as well as magnitudes in atherosclerotic disease. Classical measurements rely on reference to segments at a distance, risking inappropriate comparison between dislike vessel portions.

Objective

to explore a new method for quantifying vessel remodeling, based on the comparison between a given target segment and its inferred normal dimensions.

Methods

Geometric parameters and plaque composition were determined in 67 patients using three-vessel intravascular ultrasound with virtual histology (IVUS-VH). Coronary vessel remodeling at cross-section (n = 27.639) and lesion (n = 618) levels was assessed using classical metrics and a novel analytic algorithm based on the fractional vessel remodeling index (FVRI), which quantifies the total change in arterial wall dimensions related to the estimated normal dimension of the vessel. A prediction model was built to estimate the normal dimension of the vessel for calculation of FVRI.

Results

According to the new algorithm, “Ectatic” remodeling pattern was least common, “Complete compensatory” remodeling was present in approximately half of the instances, and “Negative” and “Incomplete compensatory” remodeling types were detected in the remaining. Compared to a traditional diagnostic scheme, FVRI-based classification seemed to better discriminate plaque composition by IVUS-VH.

Conclusion

Quantitative assessment of coronary remodeling using target segment dimensions offers a promising approach to evaluate the vessel response to plaque growth/regression.

The vulnerable coronary plaque: update on imaging technologies

Several studies have been carried out on vulnerable plaque as the main culprit for ischaemic cardiac events. Historically, the most important diagnostic technique for studying coronary atherosclerotic disease was to determine the residual luminal diameter by angiographic measurement of the stenosis. However, it has become clear that vulnerable plaque rupture as well as thrombosis, rather than stenosis, triggers most acute ischaemic events and that the quantification of risk based merely on severity of the arterial stenosis is not sufficient. In the last decades, substantial progresses have been made on optimisation of techniques detecting the arterial wall morphology, plaque composition and inflammation. To date, the use of a single technique is not recommended to precisely identify the progression of the atherosclerotic process in human beings. In contrast, the integration of data that can be derived from multiple methods might improve our knowledge about plaque destabilisation. The aim of this narrative review is to update evidence on the accuracy of the currently available non-invasive and invasive imaging techniques in identifying components and morphologic characteristics associated with coronary plaque vulnerability.

Positive remodeling is associated with vulnerable coronary plaque components regardless of clinical presentation: virtual histology-intravascular ultrasound analysis

OBJECTIVE

We used virtual histology-intravascular ultrasound (VH-IVUS) to evaluate the relation between coronary artery remodeling pattern and plaque components in 1133 patients.

METHODS

We divided the patients into two groups according to the remodeling pattern as positive remodeling (PR, remodeling index>1.05) (n=192) and intermediate remodeling (IR, remodeling index ≤ 1.05 and ≥ 0.95)/negative remodeling (NR, remodeling index<0.95) (n=941). VH-IVUS analysis classified the color-coded tissue into four major components: green (fibrotic, FT); yellow-green (fibro-fatty); white (dense calcium); and red (necrotic core, NC). Thin-cap fibroatheroma (TCFA) was defined as focal, NC-rich (≥ 10% of the cross-sectional area) plaques being in contact with the lumen in a plaque burden ≥ 40%.

RESULTS

At the minimum lumen site, PR group had greater plaque plus media area (12.8 ± 4.9 vs. 9.9 ± 3.8mm(2), p<0.001) and greater %NC area (21.7 ± 12.3 vs. 18.2 ± 11.6%, p<0.001) and smaller %FT area (57.0 ± 14.5 vs. 59.4 ± 14.6%, p=0.037) compared with IR/NR group. PR group had greater plaque volume (188 ± 150 vs. 135 ± 130 mm(3), p<0.001) and greater %NC volume (19.1 ± 9.6 vs. 16.6 ± 9.2%, p=0.001) and smaller %FT volume (58.3 ± 11.7 vs. 60.6 ± 11.0%, p=0.009) compared with IR/NR group. PR group had more TCFA compared with IR/NR group (21% vs. 13%, p=0.006). Similar findings about plaque components were observed in terms of greater %NC volume and smaller %FT volume in PR group compared with IR/NR group in patients with both acute coronary syndrome and stable angina.

CONCLUSIONS

VH-IVUS analysis demonstrates that PR was associated with more vulnerable plaque components compared with IR/NR regardless of their clinical presentation.

Optical coherence tomography: on the way to decipher the 'Rosetta stone'

Optical coherence tomography is an exciting light-based imaging modality with a much higher axial resolution as compared with intravascular ultrasound. The diagnostic value of optical coherence tomography resides in its ability to provide information on the stent interaction with the vessel wall at the level of individual struts. Chief clinical implications include evaluating strut neointimal coverage and strut malapposition following coronary stenting. This Editorial covers the basics of optical coherence tomography, its established and potential clinical implications, probable caveats and downsides, in addition to a future perspective, all in view of the late-breaking peer-reviewed literature.

Ultrasound and light: friend or foe? On the role of intravascular ultrasound in the era of optical coherence tomography

More than 20 years after its introduction, intravascular ultrasound (IVUS) has outlived many other intracoronary techniques. IVUS was useful to solve many interventional problems and assisted us in understanding the dynamics of atherosclerosis. It serves as an established imaging endpoint in large progression-regression trial and as an important workhorse in many catheterization laboratories. Nowadays, increasingly complex lesions are treated with drug-eluting stents. The application of IVUS during such interventions can be very useful. Recently, optical coherence tomography (OCT), a light-based imaging technique, has entered the clinical arena. The “omnipresence” of OCT during scientific sessions and live courses with PCI may raise in many the question: Does IVUS have a future in the “era of OCT”? Three review articles, highlighted by this editorial, demonstrate the broad spectrum of current IVUS applications and underline the significant role of IVUS during the last two decades. OCT, the much younger technique, still has to prove its value. Yet OCT is likely to take over some of the current indications of IVUS as a research tool. In addition, OCT is currently gaining clinical significance for stent optimization during complex interventional procedures. Nevertheless, there is little doubt that IVUS still has a major role in studies on coronary atherosclerosis and for guidance of coronary stenting. Thus, ultrasound and light—are they friend or foe? In fact, both methods are good in their own rights. They are complementary rather than competitive. Moreover, in combination, at least for certain indications, they could be even better.

Remodeling is a more important determinant of lumen size than atheroma burden in left main coronary artery disease

BACKGROUND

Left main coronary artery (LMCA) disease influences survival; however, the predictors of LMCA changes over time are incompletely understood.

METHODS

Paired intravascular ultrasound (IVUS) and core laboratory analyses were performed in a standardized fashion in 207 subjects (mean +/- SD age 58 +/- 10 years, 80% men). The average follow-up duration was 18 months (range 12-24 months). The IVUS measurements were first obtained at the smallest lumen area and the largest plaque area at follow-up and the corresponding positions in the LMCA were then measured at baseline.

RESULTS

The LMCA percentage of atheroma area at baseline was 38.2% +/- 11.8%, and 133 patients (64%) experienced an increase in percentage of atheroma area. Change in lumen area correlated positively with change in total vessel area (R = 0.85, P < .0001) and negatively with change in percentage of atheroma area (R = -0.58, P < .0001). Change in plaque area correlated well with change in total vessel area (R = 0.64, P < .0001) but only weakly with change in lumen area (r = 0.14, P = .039). Although LMCA length correlated negatively with baseline lumen area and total vessel area, it did not correlate with their changes over time. On multivariable analyses, current smoking predicted an increase in percentage of atheroma area (P = .0013) and plaque area (P = .0041). Height negatively predicted change in percentage of atheroma area (P = .001).

CONCLUSIONS

The LMCA lumen dimensions are more tightly linked with remodeling than with atheroma progression/regression.

Natural history of experimental coronary atherosclerosis and vascular remodeling in relation to endothelial shear stress: a serial, in vivo intravascular ultrasound study

BACKGROUND

The natural history of heterogeneous atherosclerotic plaques and the role of local hemodynamic factors throughout their development are unknown. We performed a serial study to assess the role of endothelial shear stress (ESS) and vascular remodeling in the natural history of coronary atherosclerosis.

METHODS AND RESULTS

Intravascular ultrasound-based 3-dimensional reconstruction of all major coronary arteries (n=15) was performed serially in vivo in 5 swine 4, 11, 16, 23, and 36 weeks after induction of diabetes mellitus and hyperlipidemia. The reconstructed arteries were divided into 3-mm-long segments (n=304). ESS was calculated in all segments at all time points through the use of computational fluid dynamics. Vascular remodeling was assessed at each time point in all segments containing significant plaque, defined as maximal intima-media thickness >/=0.5 mm, at week 36 (n=220). Plaque started to develop at week 11 and progressively advanced toward heterogeneous, multifocal lesions at all subsequent time points. Low ESS promoted the initiation and subsequent progression of plaques. The local remodeling response changed substantially over time and determined future plaque evolution. Excessive expansive remodeling developed in regions of very low ESS, further exacerbated the low ESS, and was associated with the most marked plaque progression. The combined assessment of ESS, remodeling, and plaque severity enabled the early identification of plaques that evolved to high-risk lesions at week 36.

CONCLUSIONS

The synergistic effect of local ESS and the remodeling response to plaque formation determine the natural history of individual lesions. Combined in vivo assessment of ESS and remodeling may predict the focal formation of high-risk coronary plaque.

MRI-based biomechanical imaging: initial study on early plaque progression and vessel remodeling

The goal of the study is to develop a noninvasive magnetic resonance imaging (MRI)-based biomechanical imaging technique to address biomechanical pathways of atherosclerotic progression and regression in vivo using a 3D fluid-structure interaction (FSI) model. Initial in vivo study was carried out in an early plaque model in pigs that underwent balloon-overstretch injury to the left carotid arteries. Consecutive MRI scans were performed while the pigs were maintained on high cholesterol (progression) or normal chow (regression), with an injection of a plaque-targeted contrast agent, Gadofluorine M. At the end of study, the specimens of carotid arterial segments were dissected and underwent dedicated mechanical testing to determine their material properties. 3D FSI computational model was applied to calculate structure stress and strain distribution. The plaque structure resembles early plaque with thickened intima. Lower maximal flow shear stress correlates with the growth of plaque volume during progression, but not during regression. In contrast, maximal principle structure stress/stain (stress-P1 and strain-P1) were shown to correlate strongly with the change in the plaque dimension during regression, but moderately during progression. This MRI-based biomechanical imaging method may allow for noninvasive dynamic assessment of local hemodynamic forces on the development of atherosclerotic plaques in vivo.

Disease progression in nonintervened saphenous vein graft segments a serial intravascular ultrasound analysis

OBJECTIVES

We used serial intravascular ultrasound (IVUS) to assess disease progression in nonintervened saphenous vein graft (SVG) segments to determine the natural rate of disease progression in SVG.

BACKGROUND

There are no serial IVUS studies of disease progression or luminal compromise in SVGs.

METHODS

We assessed serial (baseline and follow-up at 16.2 +/- 7.4 months) IVUS findings in 50 nonintervened SVG segments in 44 patients. The SVG age was 13.5 +/- 3.6 years.

RESULTS

Overall, from baseline to follow-up, plaque area increased (Delta = +0.58 +/- 1.25 mm(2), p = 0.003), and SVG and minimum lumen area (MLA) decreased (Delta = -0.50 +/- 1.14 mm(2), p = 0.002, and Delta = -1.08 +/- 1.28 mm(2), p < 0.001, respectively). The MLA decreased in 34 lesions (Delta = -1.67 +/- 1.08 mm(2)), and MLA increased in 16 lesions (Delta = +0.19 +/- 0.47 mm(2)). Compared with lesions with an increase in MLA, lesions with a decrease in MLA were associated with: 1) larger baseline SVG and plaque areas and plaque burden (15.57 +/- 3.90 mm(2) vs. 11.55 +/- 2.30 mm(2), p < 0.001; 7.97 +/- 3.77 mm(2) vs. 4.27 +/- 1.92 mm(2), p < 0.001; and 48.7 +/- 14.2% vs. 36.0 +/- 13.4%, p = 0.004, respectively); and 2) a greater decrease in SVG area (Delta = -0.96 +/- 1.05 mm(2) vs. +0.48 +/- 0.58 mm(2), p < 0.001) and greater increase in plaque area (Delta = +0.71 +/- 1.47 mm(2) vs. +0.29 +/- 0.45 mm(2), p < 0.001). The DeltaMLA correlated with both Deltaplaque area (r = -0.589, p < 0.001) and DeltaSVG area (r = 0.470, p = 0.001), and Deltaplaque area correlated with DeltaSVG area (r = 0.436, p = 0.002). There were linear relations between both the Deltaplaque area (r = 0.519, p < 0.001) and Deltalumen area (r = -0.500, p < 0.001) versus follow-up low-density lipoprotein (LDL) cholesterol; a follow-up LDL cholesterol of 100 mg/dl predicted no plaque increase.

CONCLUSIONS

Lumen loss in nonintervened SVG segments correlated with an increase in plaque area and a decrease in SVG area (plaque growth and negative remodeling) with a linear relationship between plaque growth versus follow-up LDL cholesterol leading to long-term lumen loss.

Vulnerable plaque: detection and management

Because most myocardial infarctions result from the rupture of a plaque that did not significantly compromise the coronary lumen before the event, experts widely accept that the morphology, composition, and degree of inflammation of a coronary atherosclerotic plaque is more important than the degree of luminal stenosis. Two depicting examples are the concentric, calcified lesion that shows significant luminal stenosis but is stable because of the stabilizing clasp of calcification. In contrast, a smaller but inflamed thin fibrous cap atheroma with a big lipid/necrotic core may rupture and cause an immediate fatal coronary occlusion.

Relation between plaque progression and low-density lipoprotein cholesterol during aging as assessed with serial long-term (> or =12 months) follow-up intravascular ultrasound of the left main coronary artery

Because of the clinical benefit of lipid lowering in older patients, we hypothesized that the relation between low-density lipoprotein (LDL) cholesterol serum levels and coronary plaque progression may persist throughout aging. We analyzed serial intravascular ultrasound (IVUS) data of 60 left main stems (18 +/- 9 months apart) and evaluated the relation between LDL cholesterol levels and coronary plaque progression at different ages. The population (n = 60) was divided into 3 groups according to age: tertile 1 (n = 20) was a mean age of 48 +/- 6 years (median 51, range 33 to 55), tertile 2 (n = 20) was a mean age of 58 +/- 2 years (median 59, range 55 to 61), and tertile 3 (n = 20) was a mean age of 66 +/- 6 years (median 65, range 61 to 83). Between groups, there was no significant difference in non-age-related demographics, clinical data, lipid profiles, or medications (e.g., statins). There was a positive linear relation between LDL cholesterol and annual changes in plaque plus media area in all age tertiles, which was statistically significant in tertiles 2 and 3 (r = 0.56, p <0.01; r = 0.50, p <0.02) and showed a strong trend in tertile 1 (r = 0.41, p = 0.07). The estimated LDL cholesterol thresholds, which, as determined by regression analysis, would correspond to no plaque progression, were 74, 60, and 78 mg/dl, respectively, in tertiles 1, 2, and 3. In conclusion, serial IVUS data in left main coronary arteries suggest that the relation between LDL cholesterol serum levels and plaque progression persists during aging.