Limitations of Intravascular Ultrasound for the Evaluation of Coronary Luminal Area

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Abstract
To evaluate the accuracy of intravascular ultrasound (IVUS) for the measurement of coronary luminal area, we compared IVUS with quantitative coronary angiography (QCA). We studied 46 segments in 21 patients who underwent coronary intervention. In each lesion, coronary luminal areas were evaluated by both IVUS and QCA. To quantitate the differences between the two modalities, we calculated a difference index (magnitude of intraluminal area by IVUS -intraluminal area by QCA/intraluminal area by IVUS). We also calculated an eccentricity index (the thinnest thickness of plaque divided by the width of the opposite plaque) using IVUS. All samples were classified into 2 groups according to the lumen diameter by QCA. In Group I (lumen diameter > or = 3.0 mm), we found a close correlation between the intraluminal areas obtained by the two modalities (r = 0.95, p < 0.001). In Group II (lumen diameter < 3.0 mm), we found a lower correlation between the intraluminal areas obtained by the two techniques (r = 0.61, p < 0.005), and the intraluminal area by IVUS was significantly larger than that from QCA (p < 0.001). Furthermore, there was an inverse correlation between the eccentricity index and the difference index in Group II (r = 0.83, p < 0.001). These findings indicate that the differences between ultrasonic and angiographic measurements the coronary luminal area were greater in coronary arteries with a narrow lumen due to plaque eccentricity.