Optimized expansion of the Wallstent compared with the Palmaz-Schatz stent: On-line observations with two- and three-dimensional intracoronary ultrasound after angiographic guidance

Abstract

Optimized stent expansion by high-pressure inflations of oversized balloons has initially been derived from experience obtained with the Palmaz-Schatz stent, whereas there is little experience with this strategy in the Wallstent. By using this approach with quantitative coronary angiographic guidance, 20 Wallstents and 20 Palmaz-Schatz stents were implanted in 34 patients and consecutively examined by conventional two-dimensional (2D) intracoronary ultrasound (ICUS) and three-dimensional (3D) ICUS on the basis of the application of a pattern recognition algorithm. Ultrasound criteria of adequate stent expansion were defined as a complete apposition of the stent to the vessel wall, a stent symmetry index (SSI = minimum/maximum lumen diameter) ≥0.7, and a stent-reference lumen area ratio (SRR = Minimum intrastent lumen area/Average of proximal and distal reference lumen area) ≥0.8. In all cases a smooth angiographic lumen and a negative diameter stenosis, on the basis of a distal reference, was achieved. For the Wallstents ICUS showed a higher SSI (2D, 0.95 ± 0.04 vs 0.85 ± 0.09; p < 0.001; 3D, 0.90 ± 0.09 vs 0.82 ± 0.11, p < 0.05) and a lower SRR (2D, 0.66 ± 0.12 vs 0.81 ± 0.13, p < 0.005; 3D, 0.63 ± 0.14 vs 0.74 ± 0.15, p < 0.05) than for the Palmaz-Schatz stents. Ninety percent of failure in meeting these criteria resulted from a low SRR. The incidence of incomplete stent apposition (one in both stents) or SSI <0.7 was low and generally associated with an SRR <0.8. The Wallstents met the ICUS criteria less often (2D, 2 (10%) vs 10 (50%), p < 0.01; 3D, 3 (15%) vs 9 (45%), p < 0.05), were significantly longer (35.1 ± 7.7 mm and 14.3 ± 3.3 mm, p < 0.0001), and generally demonstrated a larger vessel tapering, measured as proximal minus distal ICUS reference lumen area (1.33 ± 2.91 mm 2 vs 0.44 ± 1.97 mm 2, not significant). Wallstents meeting the ICUS criteria, however, showed less vessel tapering (0.18 ± 1.64 mm 2). Thus optimized stent expansion was followed by excellent angiographic results for both Palmaz-Schatz and Wallstent. Although angiographic results and visual assessment of the ICUS examination suggested a good outcome, few Wallstents met the ICUS criteria in contrast to the Palmaz-Schatz stents. The low value of the SRR in the Wallstents is likely to be caused by vessel tapering, suggesting that this criterion may be unsuitable in assessing the adequacy of the expansion of relatively long stents such as the Wallstent.