Relationship between residual atheroma burden and neointimal growth in patients undergoing stenting: analysis of the atherectomy before MULTI-LINK improves lumen gain and clinical outcomes trial intravascular ultrasound substudy.

OBJECTIVES: The objective of this study was to examine the relationship between quantitative volumetric and cross-sectional measures of residual atheroma burden and neointimal growth after coronary stenting. BACKGROUND: Previous intravascular ultrasound (IVUS) studies have demonstrated a correlation between residual atheroma burden and neointimal growth after coronary stenting. However, postmortem studies contradict this finding. METHODS: The study population included 34 patients who underwent IVUS six to eight months after stent placement, including 26 patients who underwent IVUS immediately after stent placement and at six to eight months follow-up. Using manual planimetry, the lumen cross-sectional area (LA), stent cross-sectional area (SA) and external elastic membrane cross-sectional area (EEM) were measured at 1-mm intervals after the procedure and at follow-up. Percent neointimal area (NA) and atheroma area (AA) were calculated as: percent neointimal area = ([SA - LA]/SA) x 100; percent AA = ([EEM - SA]/EEM) x 100 in the entire cross section and in individual quadrants. Postinterventional atheroma volume and neointimal volume at follow-up were calculated using Simpsons's rule. RESULTS: In pooled analyses using all cross sections and cross-sectional quadrants, there was a weak correlation between percent AA and NA (r = 0.11 and 0.12, respectively). Analysis in individual patients demonstrated no significant relationship between total or quadrant measurements of percent AA and NA (p = 0.47 and 0.4, respectively). No relationship between atheroma volume postintervention and neointimal volume at follow-up was observed (r = 0.1, p = 0.62). CONCLUSIONS: This study failed to demonstrate a clinically significant relationship between quantitative volumetric and cross-sectional measures of residual atheroma burden and subsequent neointimal growth.

Impact of nonmeasurable borders and variation in cross-section counts on intravascular ultrasound measurement of atherosclerotic plaque volume.

The inability to measure borders and variation in the number of 1-mm cross sections acquired from an identical length of vessel in serial intravascular ultrasound (IVUS) pullbacks represents potential errors in calculating volumes by IVUS. In a clinical IVUS trial, the percentage of nonmeasurable lumen and external elastic membrane borders, and the percent variation in the number of 1-mm cross sections acquired from an identical vessel length at 2 separate time points, were determined. A statistical model that simulated the effect of varying the percentage of the total number of cross sections in a pullback (i.e., sample fraction) was developed using SAS software. Mean and maximum errors for calculation of atheroma volume for each sample fraction were determined. The mean percentage of nonmeasurable lumen and external elastic membrane borders in an individual patient was 8.4 +/- 8.4% and 17.4 +/- 18.4%, respectively. Mean variation in the number of 1-mm cross sections acquired in serial studies was 5.6 +/- 6.2%. A decrease in sample fraction from 95% to 50% was associated with a linear increase in the mean and maximum errors in atheroma volume, from 2.0 +/- 0.9% and 5.9 +/- 3.0%, to 7.1 +/- 2.8% and 23.4 +/- 10.3%, respectively. Thus, nonmeasurable borders and variation in the number of 1-mm cross sections acquired from an identical length of vessel in serial studies are real considerations in clinical IVUS trials. However, given the reported incidence of these considerations in this clinical trial, our statistical model suggests that the impact of each of these considerations on atheroma volume calculation is small.

Variability of area measurements obtained with different intravascular ultrasound catheter systems: Impact on clinical trials and a method for accurate calibration.

BACKGROUND: Atherosclerotic plaque burden is the major end point in ongoing progression trials. Intravascular ultrasound allows precise measurements of coronary artery dimensions. However, the variability of measurements among different catheter systems is incompletely characterized. METHODS: Intravascular ultrasound imaging was performed in a cylindric phantom with 5 sections of different, known, cross-sectional area ranging from 3.24 to 27.99 mm(2). A total of 3637 measurements with different catheter systems (Atlantis SR and Ultracross, Scimed/Boston Scientific; and Invision and Avanar, Jomed) were performed. Measurements were divided into model building and validation datasets. For each catheter, calibration models were developed. RESULTS: Overestimation and underestimation of the true cross-sectional area of up to 18% was observed with different catheter systems. Calibration equations for the different systems could be developed that predicted the true diameter and area with high statistical precision (adjusted R(2) > 0.99). CONCLUSIONS: Area measurements vary among different intravascular ultrasound catheter systems. Calibration equations can correct for these differences and allow the comparison of measurements among catheters.