Mechanism of lumen enlargement with direct stenting versus predilatation stenting: influence of remodelling and plaque characteristics assessed by volumetric intracoronary ultrasound

Abstract

Objective: To compare the effects of arterial remodelling and plaque characteristics on the mechanisms of direct stenting and predilatation stenting. Direct stenting has become routine in some laboratories and differs technically from predilatation stenting.

Methods: Pre- and post-interventional volumetric intravascular ultrasound (IVUS) was undertaken in 30 patients with direct stenting and in 30 with predilatation stenting of non-calcified native coronary lesions, using the same stent design and stent length. Lumen, vessel (external elastic membrane (EEM)), and plaque (plaque + media) volumes were calculated. Remodelling was determined by comparing the EEM area at the centre of the lesion with the EEM areas at proximal and distal reference sites. Plaque eccentricity was defined as the thinnest plaque diameter to the thickest plaque diameter ratio. Plaque composition was characterised as soft, mixed, or dense.

Results: All volumetric IVUS changes were similar in the two groups. Pre-intervention remodelling remained uninfluenced after direct stenting, but was neutralised after predilatation stenting. Eccentric lesions responded to intervention by a greater luminal gain owing to greater vessel expansion in direct stenting. Plaque composition influenced luminal gain in direct stenting, the gain being greatest in the softest plaques; in predilatation stenting, luminal gain was equivalent but vessel expansion was greater for "dense" plaque and plaque reduction greater for "soft" plaque.

Conclusions: In non-calcified lesions, the mechanisms of lumen enlargement after direct or predilatation stenting are significantly influenced by atherosclerotic remodelling, plaque eccentricity, and plaque composition.

Figure 1

Representation of the method. Stent strut hypereflectivity allowed precise localisation of the proximal and distal extremities. Two 5 mm long proximal and distal reference segments were determined on both sides of the stent. Thus the total length of the analysed arterial segment was 23 mm for the 60 studied lesions (30 treated by direct stenting and 30 treated by predilatation stenting) (panel A, three dimensional reformatting). A similar 23 mm long segment was then determined on the pre-intervention imaging run, using precise landmarks. Volumetric analysis was done using intravascular ultrasound (IVUS) in 451 slices of 0.05 mm thickness. Three dimensional IVUS representations were generated by a specific digital image processing, using contour segmentation and surface rendering: (B) vessel volume (external elastic membrane (EEM)); (C) plaque (plaque + media (P+M)) and lumen volumes.

Figure 2

Influence of the pre-intervention atherosclerotic remodelling ratio on the post-intervention remodelling ratio after direct and indirect stent implantation. The pre-intervention remodelling ratio remained uninfluenced after direct stenting (DS), but was neutralised after predilatation stenting (PDS).

Figure 3

Example of three dimensional IVUS representations of plaque changes before and after intervention (during direct stenting). (A) Plaque with pre-intervention positive remodelling (ratio = +16%), the post-intervention changes in lumen, vessel (external elastic membrane (EEM)), and plaque (plaque + media (P+M)) volumes are 127 mm³, 118 mm³, −9 mm³. The post-intervention remodelling ratio is +27%. The mean diameter of the coronary artery is 4.3 mm. (B) Plaque with pre-intervention negative remodelling (ratio = −30%), the post-intervention changes in lumen, EEM, and P+M volumes are 45 mm³, 33 mm³, −12 mm³. The post-intervention remodelling ratio is −22%. The mean diameter of the coronary artery is 3.2 mm.