Background: Acute myocardial infarction (AMI) causes a decline in renal function. This study aimed to elucidate the longitudinal association between physical activity levels and changes in renal function up to 6 months after the onset of AMI. Methods: In this dual-center prospective observational study, 73 AMI patients (67 men; average age, 65.0±11.7 years) were enrolled from 2017 to 2019. Blood biochemistry, urinalysis, and physical function tests were conducted at discharge and 3 and 6 months post-discharge. The renal function was evaluated based on cystatin C-based estimated glomerular filtration rate (eGFRcys). The number of steps was recorded for 6 months post-discharge. Generalized estimating equation (GEE) models were used to test the longitudinal association between physical activity levels and within-patient changes in eGFRcys. Both GEE models with a follow-up period of 3 and 6 months were constructed to assess the effects of the passage of time. Results: Patients were stratified into the low (n=36; 2903±1187 steps/day) and high groups (n=37; 7988±3192 steps/day) based on the median number of steps. Both GEE models at the 3- (p=0.027) and 6-month follow-up (p=0.034) showed a significant positive association between the physical activity levels and within-patient changes in eGFRcys. The changes in eGFRcys at 6 months were −0.3 mL/min/1.73 m2 and +4.4 mL/min/1.73 m2 among the low and high group participants, respectively. Conclusions: There was a significant positive association between physical activity and renal function changes after the onset of AMI, which persisted when the follow-up period was extended from 3 to 6 months. Our findings support the importance of interventions that enable maintaining high physical activity levels as a strategy for preserving renal function in AMI patients.
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