A 72-year-old man with exertional chest pain was transferred to our hospital. He had undergone the implantation of a bare metal stent and two drug-eluting stent in his left anterior descending artery (LAD) 13, 12 and 1 years before the current admission, respectively. He had experienced several episodes of in-stent restenosis (ISR). Finally, plain old balloon angioplasty (POBA) had failed with an apparent balloon indentation a month prior to this admission at the previous hospital.

Electrocardiogram: Sinus rhythm, heart rate of 62 beats, complete right bundle branch block.Laboratory data: Creatinine 1.02 mg/dL, hemoglobin A1c 6.5 %, LDL-cholesterol 28 mg/dL, brain natriuretic protein 37.8 pg/mL.Echocardiography: Ejection fraction of 45 %, left ventricle diastolic diameter 50 mm, moderate hypokinesis in antero-septal and apical regions.

Initial angiography showed severe ISR in the LAD with a fractional flow reserve of 0.67 measured at the previous hospital. We also observed significant stenosis in the middle LAD, with obvious angiographic evidence of stent under-expansion.

Following the unsuccessful POBA, it was decided that additional interventions were necessary. Optical coherence tomography (OCT) revealed that the target lesion was not due to new intimal calcification but was primarily a result of poor stent expansion and calcification beneath the stents. Consequently, we opted for excimer laser coronary angioplasty (ELCA, X-80, USA, Spectranetics) without saline flushing technique at 80 J and 80 Hz, to modify the calcium-plaque located beneath the stents and to increase the output power. Subsequently, we dilated the lesion with 3.0 mm non-compliant balloon at nominal pressure and up to 30 atm, eliminating the balloon indentation. Finally, a drug-coated balloon was applied. OCT confirmed sufficient stent expansion and the successful cracking of calcification beneath the previously implanted stents. The final angiography showed no residual stenosis. Two years after this procedure, the patient remained asymptomatic.

Stent under-expansion is a significant factor contributing to ISR. However, stent under-expansion can sometimes occur due to the presence of underestimated hard plaque. ELCA is a unique modality for modifying hard plaque beneath stents through photochemical, photothermal, and photomechanical effects. A study demonstrated that ELCA for ISR was associated with a larger final minimum lumen area and a greater stent area compared to previously implanted stents, potentially breaking the vicious circle. Although saline flushing with ELCA led to a lower incidence of coronary dissection, the non-flushing technique could enhance the effect when appropriately indicated, as in the case of ISR.