Mechanisms and treatment outcomes of ostial right coronary artery in-stent restenosis

Background: Despite a high rate of in-stent restenosis (ISR) after stenting the right coronary artery (RCA) ostium, the mechanism of ostial RCA ISR is not well understood.Aims: We aimed to clarify the cause of ostial RCA ISR using intravascular ultrasound (IVUS).Methods: Overall, 139 ostial RCA ISR lesions were identified with IVUS, pre-revascularisation. Primary ISR mechanisms were classified as follows: 1) neointimal hyperplasia (NIH); 2) neoatherosclerosis; 3) ostium not covered by the stent; 4) stent fracture or deformation; 5) stent underexpansion (old minimum stent area <4.0 mm2 or stent expansion <50%); or 6) a protruding calcified nodule.Results: The median duration from prior stenting was 1.2 (first quartile 0.6, third quartile 3.1) years. The primary mechanisms of ISR were NIH in 25% (n=35) of lesions, neoatherosclerosis in 22% (n=30), uncov-ered ostium in 6% (n=9) (biological cause 53%, n=74), stent fracture or deformation in 25% (n=35), under -expansion in 11% (n=15), and protruding calcified nodules in 11% (n=15) (mechanical cause 47%, n=65). Including secondary mechanisms, 51% (n=71) of ostial RCA ISRs had stent fractures that were associated with greater hinge motion of the ostial-aorta angle during the cardiac cycle. The Kaplan-Meier rate of target lesion failure at 1 year was 11.5%. When the mechanically caused ISRs were treated without new stents, they suffered a higher subsequent event rate (41.4%) compared with non-mechanical causes or mechanical causes treated without restenting (7.8%, unadjusted hazard ratio 6.44, 95% confidence interval: 2.33-17.78; p<0.0001).Conclusions: Half of the ostial RCA ISRs were due to mechanical causes. Subsequent event rates were high, especially in mechanically caused ISRs treated without the implantation of a new stent.

Automated summary

Using intravascular ultrasound (IVUS), this study aimed to clarify the cause of in-stent restenosis (ISR) in the ostium of the right coronary artery (RCA). The main mechanisms found were neointimal hyperplasia, neoatherosclerosis, uncovered ostium, stent fracture or deformation, stent underexpansion, and protruding calcified nodules. Half of the ISR cases were due to mechanical causes, and treating mechanically caused ISR without new stent implantation led to a higher subsequent event rate.