Methods:  We studied retrospectively all patients with KD presenting to our hospital over a 10-year period. Patients were categorized as having received one of three durations of HDA: 0, 1-7, or >7 days. The primary outcome was the maximum coronary artery Z-score measured by transthoracic echocardiography; secondary outcomes included C-reactive protein (CRP) and platelet count at diagnosis, 4-8 weeks, and at 9-15 months from presentation. Longitudinal data were analyzed using a linear mixed model.

Results:  103 patients with KD had HDA duration documented and were included in the analysis; 35 of those patients had CAAs at diagnosis. Within the overall study population, there was no difference in patient age, sex, race, KD status (classic versus incomplete KD), or CRP and platelet count at diagnosis between the three HDA groups. The 17 patients who received no HDA had longer duration of illness prior to diagnosis and were less likely to have received IVIg; twelve of these 17 patients defervesced prior to diagnosis. There was no difference in HDA duration between patients with and without CAAs at the time of diagnosis. Among patients with CAAs at the time of diagnosis, linear regression analysis adjusted for age, sex, and IVIg resistance revealed that HDA duration did not predict coronary artery dimensions at 9-15 months. Similarly-adjusted longitudinal analysis demonstrated no difference in the rate of decline of coronary artery Z-score, CRP, or platelet count between the three HDA groups. The only factors associated with higher coronary artery Z-scores at 9-15 months were higher coronary artery Z-scores at diagnosis and older age at diagnosis.

Conclusion:  In patients with KD, a longer duration of illness before diagnosis and lack of administration of IVIg were clinical correlates associated with not administering HDA. This is a subset of patients in whom defervescence occurred prior to diagnosis as part of a prolonged illness course. Among all of the patients, the coronary artery Z-score at diagnosis and age at diagnosis were the only predictors of coronary artery Z-score at 9-15 months. The duration of HDA administration had no apparent effect on clinically-relevant outcome measures, particularly the persistence of CAAs.