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Background Coronary arterial aneurysms (CAAs) associated with Kawasaki disease (KD) significantly affect prognosis. However, the clinical course of CAAs and factors associated with CAA regression have not been well analyzed. Methods and Results The cohort of the Z‐Score 2nd Project Stage study, a multicenter, retrospective, cohort study involving 44 institutions in Japan including 1006 patients with KD, was examined. CAAs were classified by the z score of their internal diameter in the acute phase: small ( z z z ≥10). The lower limit of small CAA was based on the Japanese Ministry of Health, Labour and Welfare criteria. In the right coronary artery, the CAA regression rates 10 years after diagnosis were 95.5% for small, 83.2% for medium, and 36.3% for large. In the proximal left anterior descending artery, the regression rates 10 years after diagnosis were 95.3% for small, 80.1% for medium, and 28.8% for large. Cox regression analysis showed that diagnosis under the age of 1 year and onset of KD in 2010 to 2012 for the right coronary artery and the left anterior descending artery, and female for the right coronary artery were significantly associated with a high regression rate, whereas large CAAs for the right coronary artery and the left anterior descending artery were significantly associated with a low regression rate. Conclusions The current study, the largest Japanese study of its kind, found that small aneurysm, recent onset, and diagnosis under the age of 1 year predict regression, and that even giant aneurysms could regress. These data may contribute to long‐term management of coronary aneurysms. Registration URL: https://www.umin.ac.jp/ctr/ ; Unique identifier: UMIN000010606.

Background Development of right ventricular ( RV ) hypertension eventually contributes to RV and left ventricular ( LV ) myocardial fibrosis and dysfunction. The molecular mechanisms are not fully elucidated. Methods and Results Pulmonary artery banding was used to induce RV hypertension in rats in vivo. Then, we evaluated cardiac function and regional remodeling 6 weeks after pulmonary artery banding. To further elucidate mechanisms responsible for regional cardiac remodeling, we also mimicked RV hypertensive stress by cyclic mechanical stretching applied to confluent cultures of cardiac fibroblasts, isolated from the RV free wall, septal hinge points, and LV free wall. Echocardiography and catheter evaluation demonstrated that rats in the pulmonary artery banding group developed RV hypertension with leftward septal displacement, LV compression, and increased LV end‐diastolic pressures. Picrosirius red staining indicated that pulmonary artery banding induced marked RV fibrosis and dysfunction, with prominent fibrosis and elastin deposition at the septal hinge points but less LV fibrosis. These changes were associated with proportionally increased expressions of integrin‐β1 and profibrotic signaling proteins, including phosphorylated Smad2/3 and transforming growth factor‐β1. Moreover, mechanically stretched fibroblasts also expressed significantly increased levels of α‐smooth muscle actin, integrin‐β1, transforming growth factor‐β1, collagen I deposition, and wrinkle formation on gel assays, consistent with myofibroblast transformation. These changes were not observed in parallel cultures of mechanically stretched fibroblasts, preincubated with the integrin inhibitor ( BTT ‐3033). Conclusions Experimentally induced RV hypertension triggers regional RV , hinge‐point, and LV integrin β1‐dependent mechanotransduction signaling pathways that eventually trigger myocardial fibrosis via transforming growth factor‐β1 signaling. Reduced LV fibrosis and preserved global function, despite geometrical and pressure aberrations, suggest a possible elastin‐mediated protective mechanism at the septal hinge points.