SIGNIFICANCE OF AUTOMATED STENOSIS DETECTION DURING QUANTITATIVE ANGIOGRAPHY - INSIGHTS GAINED FROM INTRACORONARY ULTRASOUND IMAGING

Background Automated stenosis analysis is a common feature of commerci ally available quantitative coronary angiography (QCA) systems, allowi ng automatic detection of the boundaries of the stenosis, interpolatio n of the expected dimensions of the coronary vessel at the point of ob struction, and angiogaphically derived estimation of atheromatous plaq ue size. However, the ultimate meaning of this type of analysis in ter ms of the degree of underlying atherosclerotic disease remains unclear . We investigated the relationship between stenosis analysis performed with QCA and the underlying degree of atherosclerotic disease judged by intracoronary ultrasound (ICUS) imaging. Methods and Results In 40 coronary stenoses, automated identification of the sites of maximal lu minal obstruction and the start of the stenosis was performed with QCA by use of curvature analysis of the obtained diameter function. Plaqu e size at these locations also was estimated with ICUS, with an additi onal ICUS measurement immediately proximal to the start of the stenosi s. Crescentlike distribution of plaque, indicating an atheroma-free ar e of the arterial wall, was recorded. At th site of the obstruction, t otal vessel area measured with ICUS was 16.65+/-4.04 mm(2), whereas an equivalent measurement obtained from QCA-interpolated reference dimen sions was 7.48+/-3.30 mm(2) (P=.0001). Plaque area derived from QCA da ta was significantly less than that calculated from ICUS (6.32+/-3.21 and 13.29+/-4.22 mm(2), respectively; mean difference, 6.92+/-4.43 mm( 2); P=.0001). At the start of the stenosis identified by automated ana lysis, ICUS plaque area was 9.38+/-3.17 mm(2), and total vessel area w as 18.77+/-5.19 mm(2) (50+/-11% total vessel area stenosis). The arter ial wall presented a disease-free segment in 28 proximal locations (70 %) but in only 5 sites (12%) corresponding to the start of the stenosi s and none at the obstruction (P=.0001). At the site of obstruction, a ll vessels showed a complete absence of a disease-free segment, and th e atheroma presented a cufflike or all-around distribution with a vari able degree of eccentricity. Conclusions At the site of maximal obstru ction, QCA underestimated plaque size as measured with ICUS. Atheroscl erotic disease was consistently present at the start of the stenosis a nd was used as a reference site by automated stenosis analysis. At the start of the stenosis, ICUS demonstrated a mean 50+/-11% total vessel area stenosis; with a characteristic loss of disease-free arcs of art erial wall present in proximal locations. Thus, the site identified by automated stenosis analysis as the start of the stenosis does not rep resent a disease-free site but rather the place where compensatory ves sel enlargement fails to preserve luminal dimensions, a phenomenon tha t seems related to the observed loss of a remnant are of normal arteri al wall.