Impact of coronary artery remodeling on misinterpretation of angiographic disease eccentricity: evidence from intravascular ultrasound

Fibrous Cap Thickness Predicts Stable Coronary Plaque Progression: Early Clinical Validation of a Semiautomated OCT Technology

BACKGROUND

Imaging-based characteristics associated with the progression of stable coronary atherosclerotic lesions are poorly defined. Utilizing a combination of optical coherence tomography (OCT) and intravascular ultrasound (IVUS) imaging, we aimed to characterize the lesions prone to progression through clinical validation of a semiautomated OCT computational program.

METHODS

Patients with stable coronary artery disease underwent nonculprit vessel imaging with IVUS and OCT at baseline and IVUS at the 12-month follow-up. After coregistration of baseline and follow-up IVUS images, paired 5-mm segments from each patient were identified, demonstrating the greatest plaque progression and regression as measured by the change in plaque burden. Experienced readers identified plaque features on corresponding baseline OCT segments, and predictors of plaque progression were assessed by multivariable analysis. Each segment then underwent volumetric assessment of the fibrous cap (FC) using proprietary software.

RESULTS

Among 23 patients (70% men; median age, 67 years), experienced-reader analysis demonstrated that for every 100 μm increase in mean FC thickness, plaques were 87% less likely to progress (P = .01), which persisted on multivariable analysis controlling for baseline plaque burden (P = .05). Automated FC analysis (n = 17 paired segments) confirmed this finding (P = .01) and found thinner minimal FC thickness (P = .01) and larger FC surface area of <65 μm (P = .02) and <100 μm (P = .04) in progressing segments than in regressing segments. No additional imaging features predicted plaque progression.

CONCLUSIONS

A semiautomated FC analysis tool confirmed the significant association between thinner FC and stable coronary plaque progression along entire vessel segments, illustrating the diffuse nature of FC thinning and suggesting a future clinical role in predicting the progression of stable coronary artery disease.

Assessment of coronary stenosis, plaque burden and remodeling by multidetector computed tomography in patients referred for suspected coronary artery disease

AIMS

To compare multidetector computed tomography (MDCT) with intravascular ultrasound (IVUS) and invasive quantitative coronary angiography (QCA) for assessment of coronary lesions in patients referred for suspected coronary artery disease (CAD).

METHODS AND RESULTS

We studied 57 patients (48 men; mean age: 63 ± 10 years) who underwent 64-slice MDCT because of atypical chest pain, stable angina, or ECG abnormalities and were diagnosed with CAD. All patients subsequently underwent QCA and IVUS. We analyzed 102 coronary lesions using the three techniques. Measurements of luminal area stenosis and cross-sectional area by MDCT (72.9 ± 7.0% and 4.5 ± 1.8 mm, respectively) were in good agreement with those by IVUS [72.7 ± 6.7% and 4.5 ± 1.6 mm, respectively; Lin's concordance correlation coefficient r = 0.847; 95% confidence interval (CI) = 0.792-0.902 and r = 0.931; 95% CI = 0.906-0.956, respectively] but not QCA (r = 0.115; 95% CI = 0.040-0.189 and r = 0.433; 95% CI = 0.291-0.576, respectively). Plaque cross-sectional area and plaque volume measured by MDCT (12.4 ± 3.8 mm and 104.7 ± 52.8 microl, respectively) were in good agreement with those by IVUS (12.2 ± 3.7 mm and 102.8 ± 54.1 microl; r = 0.913; 95% CI = 0.880-0.945 and r = 0.979; 95% CI = 0.969-0.990, respectively). Remodeling index measurements by MDCT (1.22 ± 0.22) were in good agreement with those by IVUS (r = 0.876; 95% CI = 0.831-0.922). Positive remodeling occurred in 63% of stenoses.

CONCLUSION

MDCT allows accurate noninvasive assessment of coronary stenosis, plaque burden and remodeling in patients referred for suspected CAD. Positive remodeling is a frequent finding in stable lesions.

Risk factor management: antiatherogenic therapies

Despite the advances in interventional techniques, the management of stable atherosclerosis remains the domain of optimal guideline-oriented therapy. Recent studies on the effects of aggressive lipid lowering on atheroma volume changes using intravascular ultrasound indicate that it is possible to achieve atherosclerosis regression by reaching low-density lipoprotein (LDL) levels less than 75 mg/dl. The pleiotropic anti-inflammatory effects of statins contribute to the reduction of cardiovascular (CV) event observed with aggressive lipid lowering. As a second important strategy to prevent disease progression, lifestyle changes with regular physical exercise are capable of halting the atherosclerotic process and reducing angina symptoms and CV events. Optimal medical therapy, a healthy lifestyle with regular physical exercise, and coronary interventions are not mutually exclusive treatment strategies. Over the last few decades, both have proved to be effective in significantly reducing the CV mortality in the Western world. However, risk factor modification contributed to at least half the effect in the reduction of CV mortality. This figure provides an estimate of what could be achieved if we were to take risk factor modification more seriously – especially in the acute care setting. The knowledge is there: today we have a better understanding on how to stop progression and even induce regression of atherosclerosis. Much research still needs to be done and will be done. In the meantime, however, our primary focus should lie in implementing what is already known. In addition, it is essential not just to treat CV risk factors, but also to treat them to achieve the target values as set by the guidelines of European Society of Cardiology.

Comparison of intravascular ultrasound and angiographic assessment of coronary reference segment size in patients with type 2 diabetes mellitus

During percutaneous coronary intervention, the reference segment is assessed angiographically. This report described the discrepancy between angiographic and intravascular ultrasound (IVUS) assessment of reference segment size in patients with type 2 diabetes mellitus. Preintervention IVUS was used to study 62 de novo lesions in 41 patients with type 2 diabetes mellitus. The lesion site was the image slice with the smallest lumen cross-sectional area (CSA). The proximal and distal reference segments were the most normal-looking segments within 5 mm proximal and distal to the lesion. Plaque burden was measured as plaque CSA/external elastic membrane (EEM) CSA. Using IVUS, the reference lumen diameter was 2.80 +/- 0.42 mm and the reference EEM diameter was 4.17 +/- 0.56 mm. The angiographic reference diameter was 2.63 +/- 0.36 mm. Mean difference between the IVUS EEM diameter and angiographic reference diameter was 1.56 +/- 0.55 mm. The mean difference between the IVUS reference lumen diameter and angiographic reference lumen diameter was 0.18 +/- 0.44 mm. Plaque burden in the reference segment correlated inversely with the difference between IVUS and quantitative coronary angiographic reference lumen diameter (slope = -0.12, 95% confidence interval -0.17 to -0.07, p <0.001), but it was not related to the absolute angiographic reference lumen diameter. Thus, reference segment diameters in type 2 diabetic patients were larger using IVUS than angiography, especially in the setting of larger plaque burden. In conclusion, these findings combined with inadequate remodeling may explain the angiographic appearance of small arteries in diabetic patients.

Comparison of intravascular ultrasound and quantitative coronary angiography for the assessment of coronary artery disease progression

BACKGROUND

The relative merits of quantitative coronary analysis (QCA) and intravascular ultrasound (IVUS) for the assessment of progression/regression in coronary artery disease are uncertain. To explore this subject further, we analyzed the angiographic and IVUS data derived from a contemporary clinical trial population.

METHODS AND RESULTS

We investigated the relationships between QCA and IVUS at single time points (n=525) and also for the changes over time (n=432). QCA and IVUS data underwent central laboratory analyses. Statistically significant correlations were observed between the QCA coronary artery score and the IVUS-derived lumen volume (r=0.65, P<0.0001) and total vessel volume (r=0.55, P<0.0001) and between the QCA cumulative coronary stenosis score and percent atheroma volume on IVUS (r=0.32, P<0.0001) at baseline for matched segments. A similar pattern of correlations was observed for global (all segments) QCA-derived and single-vessel IVUS-derived data. There were statistically significant but weak correlations between the changes over time in lumen dimensions on QCA and IVUS (P=0.005) and between the change in cumulative coronary stenosis score on QCA and percent atheroma volume on IVUS (r=0.14, P=0.01). Nevertheless, patients with and without angiographic progression had changes in plaque volume on IVUS of 9.13 and 0.20 mm3, respectively (P=0.028).

CONCLUSIONS

QCA- and IVUS-derived measures of lumen dimensions are correlated at single time points and for changes over time. Although the change in percent atheroma volume is only weakly correlated with QCA changes as continuous variables, disease progression on QCA is associated with significant increases in plaque volume on IVUS compared with no angiographic progression.

The eccentric lumenology

Coronary angiography has a poor predictive value for the detection of eccentric plaque morphology. Many reports have demonstrated discordance between the angiographic classification and the intravascular ultrasound (IVUS) classification. Although eccentricity is usually considered a dichotomous character, more than two-thirds of all coronary stenosis have some degree of eccentricity. The American College of Cardiology/American Heart Association (ACC/AHA) Task force included lesion eccentricity as a risk factor for moderate procedural success (60-85%) and moderate complications (type B). Although lesion eccentricity has been implicated as a risk factor for reduced short-term procedural results, current available data does not support the adverse impact of eccentricity on procedural success or restenosis. The present article reviews the incidence and the various clinical scenarios known to be associated with the eccentric lumenogram and the impact of coronary artery remodeling contributing to misinterpretation of disease eccentricity. Various therapeutic modalities with reference to eccentric lesions are also considered.

Effect of Simvastatin on Coronary Lesion Site Remodeling: A Serial Intravascular Ultrasound Study

BACKGROUND

Direct evidence of coronary artery remodeling can be derived only from serial changes in the external elastic membrane (EEM) and plaque area. The aim of the study was to assess the effect of simvastatin on coronary remodeling in serial intravascular ultrasound (IVUS) studies.

METHODS

In 39 male patients ECG-triggered transducer pullback IVUS was performed at baseline, after 3 months on a lipid-lowering diet (control period), and after another 12 months of simvastatin 40 mg/day. The lesion site was the image slice with maximum plaque burden at 3 months.

RESULTS

Absolute changes in the EEM area correlated significantly with changes in plaque area during the control period [B = 0.966, r = 0.792 (95% CI 0.71-1.22); p < 0.001] and during simvastatin treatment [B = 0.945, r = 0.822 (95% CI 0.73-1.16); p < 0.001], but there was no significant difference in the slope (delta EEM/delta plaque) between the two time intervals. After 12 months of simvastatin, there was a significant reduction in the lesion EEM area of 4.6% (p = 0.006) and in the lesion plaque area of 5.9% (p < 0.001), but there was no change in reference measurements. As a result, the remodeling index was reduced by simvastatin from 1.01 +/- 0.12 to 0.95 +/- 0.09 (p < 0.001).

CONCLUSION

Simvastatin decreases the remodeling index by reducing lesion, but not reference plaque and EEM area. However, simvastatin does not affect direct evidence of remodeling (delta EEM/delta plaque) obtained using serial IVUS studies.

Carotid stenosis degree in CT angiography: assessment based on luminal area versus luminal diameter measurements

The aim of this study was to investigate CT angiography (CTA) luminal area measurements in the assessment of carotid artery stenosis compared with the current clinically used criteria based on lumen diameter measurements. Seventy-two vessels in 36 patients were evaluated by CTA and digital subtraction angiography (DSA). Two observers measured area and diameter stenosis degrees using automated 3D CTA analysis software. The ratio of the largest/smallest luminal diameter at the level of maximal stenosis (L/S ratio) was used to describe lumen morphology. Diagnostic agreement between CTA and DSA was calculated. For the assessment of area stenosis, interobserver and intraobserver correlation coefficients were 0.898 and 0.906 (p<0.001). The correlation coefficient between the diameter stenosis and area stenosis was lower in stenoses with extremely noncircular lumen (L/S ratio>or=1.5) (r=0.797, p<0.001) compared with stenoses with circular lumen (LS ratio<1.2) (r=0.978, p<0.001). Only satisfactory agreement (kappa 0.54-0.77, p<0.001) was obtained between area stenosis on CTA and diameter stenosis on DSA. Assessment of stenosis degree with area measurements on 3D CTA proved to be reproducible. Area stenosis provides a less-severe estimate of the degree of carotid stenosis but might theoretically express the real hemodynamic significance of the lesion better than diameter stenosis, especially in stenoses with noncircular lumen.

Effect of disease eccentricity on compensatory remodeling of coronary arteries: evidence from intravascular ultrasound before interventions

BACKGROUND

Compensatory remodeling occurs to maintain lumen area in human coronary vessels. However, few data exist regarding the relationship between vessel remodeling and plaque distribution. Therefore, we studied coronary sites with or without remodeling by intravascular ultrasound and correlated with disease distribution.

METHODS AND RESULTS

A total of 90 coronary sites with significant stenosis (>50%) from 80 patients were examined before interventions. For identifying the vessel remodeling, external elastic membrane (EEM) area was measured at the stenotic sites and the adjacent proximal and distal sites. The reference EEM area was calculated by averaging proximal and distal EEM areas, and percent enlargement of the EEM area was calculated by the formula: [(stenosis EEM area-reference EEM area)/reference EEM area]x100. Plaque area was determined by reducing the lumen from EEM areas. The maximal (max) and minimal (min) distances from the center of the lumen to the EEM were also measured, and the disease eccentricity index was calculated by the formula: [(max-min)/max]. The lesion was defined as eccentric if the index was >0.5 and as concentric if <or=0.5. There were 39 eccentric and 51 concentric lesions. The enlargement remodeling was observed at 32 lesions with the enlargement of EEM area of 28.0+/-16.0% (5.5 to 71.3%). Enlargement was more frequently observed in the eccentric than in concentric lesions (P<0.05). However, within 32 stenoses, which showed enlargement, there was no difference in enlargement between eccentric (n=19, 25.6+/-21.0%) and concentric lesions (n=13, 21.5+/-12.0%). Also, there was no statistical correlation between the increase in plaque area and % enlargement of EEM area irrespective of plaque morphology.

CONCLUSIONS

These data demonstrate that in advanced coronary disease compensatory enlargement occurs more frequently at the eccentric than concentric coronary lesions. However, the EEM area was limited to expand regardless of the disease morphology.

Coronary disease morphology and distribution determined by quantitative angiography and intravascular ultrasound--re-evaluation in a cooperative multicenter intravascular ultrasound study (COMIUS)

Although previous studies have demonstrated that even quantitative coronary angiography (QCA) can not provide accurate disease morphology, there has not been a systematic comparison of disease morphology determined by QCA and intravascular ultrasound (IVUS), particularly in Japanese patients. Therefore, the present study prospectively examined patients in a multicenter cooperative study. A total of 491 coronary sites from 562 patients (446 men, 116 women; mean age, 64+/-11 years) who underwent coronary interventions were enrolled. The target lesions (>50% diameter stenosis) were evaluated pre-operatively by both QCA and IVUS operating at 30-40 MHz and the percent area stenosis, eccentricity index (EI) and lesion length were determined. The minimal (min) and maximal (max) distances from the center of the stenotic lesion to the outline of the vessel wall were measured, and the EI was calculated by the formula: [(max - min)/max]. By QCA, lesion length was determined by measuring the distance between the proximal and distal shoulders of the lesion. When the lesions were observed by IVUS with a motorized pull-back system, the length was calculated by multiplying the time for observation of the disease and 0.5 or 1 mm/s. Although the severity of the stenosis determined by QCA (86+/-10%, mean +/- SD) did not differ from that by IVUS (83+/-13%), there was no correlation between them (r=0.32, y=0.25x+65) and the correlation did not improve when lesions with remodeling, enlargement (n=176) or shrinkage (n=79) were omitted from the calculation. The EIs by QCA and IVUS were 0.51+/-0.26 and 0.52+/-0.22, respectively (NS), and there was no correlation between them (r=0.30, y=0.36x+33). However, when the lesions with remodeling were excluded, the correlation greatly improved (r=0.80, y=0.84x+10.6, p<0.05). Lesion length determined by QCA (12.4+/-6.1 mm) was significantly shorter than that by IVUS (16.3+/-8.9 mm, p<0.01). These results demonstrate that coronary angiography significantly misinterprets disease morphology in terms of severity, eccentricity and length, in part because of vessel remodeling that can be accurately determined only by IVUS.