In addition, a comparison between the patients with SR and patients with AF of the same age showed that the mRNA expression levels of MMP-9 and Bax in the two age groups of patients with AF showed significant upward-regulation trends (P < 0.05), especially in elderly patients with AF, so this upward trend was the most obvious (P < 0.05). The gene discussed is BAX; the disease is atrial fibrillation.