Coronary stent implantation in acute vessel closure 48 hours after an unsatisfactory coronary angioplasty

Artifacts in intravascular ultrasound imaging during coronary artery stent implantation

Intravascular ultrasound imaging is able to provide direct images of the stent meshwork. However, a paradoxical question remains unanswered: Why is it not possible to correct or prevent implantation defects by ultrasound-guided implantation? We postulate that these discrepancies are due to image artifacts. We performed an in vitro experiment allowing detection, physical characterization, and computerized simulations of the various aspects of these artifacts. The width of the echo of a strut is variable, dependent on its distance from the transducer. The stent strut echo orientation is variable, and depends on the position of the transducer inside the stent. The stent contour image depends on the position of the transducer. In conclusion, knowledge of these stent intravascular ultrasound image artifacts enabled us to discriminate accurately between artifacts and real stent implantation defects, and are indispensable for accurate qualitative and quantitative analyses of stents.

Intravascular ultrasound after low and high inflation pressure coronary artery stent implantation

OBJECTIVES

We sought to characterize the differences seen after low or high pressure coronary artery stent deployment as assessed by intravascular ultrasound.

BACKGROUND

Until 1992, the success of stent deployment was assessed by angiographic criteria only, but in 1993 the procedure was expanded to include postprocedural single-use intravascular ultrasound imaging. Ultrasound criteria for successful stent deployment were 1) symmetry, 2) minimal lumen diameter > 3.0 mm, 3) no echo-free spaces between the stent and the vessel, and 4) no uncovered dissections.

METHODS

We used mechanical 4.8F or 3.5F 20- or 30-MHz monorail single-use intravascular ultrasound catheters.

RESULTS

Fifty-two patients were included, 28 treated in 1991 and 1992 (group A) and 24 treated in 1993 or 1994 (group B); 87% of patients underwent elective stent implantation. The number of echocardiographic studies per patient increased from 1 +/- 0.1 (mean +/- SD) in group A to 2.0 +/- 0.85 in group B. Mean maximal balloon size increased from 3.3 +/- 0.33 to 3.73 +/- 0.24 mm and maximal inflation pressure from 6.9 +/- 1.1 to 15.8 +/- 2.4 bar (p < 0.001). The eccentricity index was 0.915 +/- 0.04 in group B versus 0.87 +/- 0.05 in group A. Minimal lumen diameter measured by echocardiography increased from 2.55 +/- 0.41 mm in group A to 3.14 +/- 0.37 mm in group B. The final mean values per cross-sectional area as a percent of calculated balloon area were similar in group A (67.5 +/- 23%) and group B (66.5 +/- 22.9%). No major acute complications occurred in either group; subacute thrombosis developed in two patients, both in group A.

CONCLUSIONS

Intravascular ultrasound data confirm that high pressure stent deployment leads to increased minimal lumen area. Despite high pressure stent deployment, homogeneous stent geometry and optimal stent expansion were not observed in all patients.

Vascular pathology of balloon-expandable flexible coil stents in humans

The morphologic changes in atherosclerotic coronary arteries and saphenous vein bypass grafts after placement of a balloon-expandable flexible coil stent (Cook) are described. In each case, the vessels were patent despite morphologic evidence of injury and dissection in the vessel wall. The stented region was reendothelialized and the tissue overlying the stent wires consisted primarily of smooth muscle cells. There was minimal inflammatory reaction to the stent wires. These findings suggest that the balloon-expandable flexible coil stent can effectively maintain vessel patency even in the setting of postangioplasty lumen disruption. In addition, the vessels tolerate the metal prosthesis with little evidence of tissue inflammatory reaction.