Objectives To identify clinical characteristics of patients with non-refractory Kawasaki disease (KD), which were defined as those who successfully responded to the standard initial intravenous immunoglobulin (IVIG) treatment (2 g/kg/day, single infusion) without any secondary or later additional specific treatments, and to investigate the factors associated with the development of coronary artery (CA) complications in patients with non-refractory KD.

Design Retrospective cohort study.

Setting Hospitals specialising in paediatrics and hospitals with ≥100 beds and a paediatric department throughout Japan.

Patients A total of 122 489 patients who developed KD across Japan during 2011–2018.

Main outcome measures CA abnormalities identified after acute illness of KD (defined as CA sequelae).

Results A total of 69 735 patients with non-refractory KD were identified, of which 672 (0.96%) experienced CA sequelae. Among patients with non-refractory KD, the presence of CA abnormalities identified at initial echocardiographic assessment was strongly associated with CA sequelae (adjusted OR (95% CI): 37.8 (31.9 to 44.7)). CA sequelae was also associated with male patients, infants (<12 months old), older patients (≥60 months old) and patients who received delayed initial IVIG treatment (>7 days from KD onset). Subgroup analyses demonstrated that delayed initial IVIG treatment was significantly associated with the development of CA sequelae in both patients with and without CA abnormalities identified at initial echocardiographic assessment.

Conclusions Approximately 1% of patients with non-refractory KD may develop CA sequelae. Our findings highlight the importance of initial echocardiographic assessment and early initiation of IVIG treatments for patients with KD.