The major findings of this study are that: (1) in patients who underwent emergency PCI for AMI, AKI was present in 82 (9.4%), and of the AKI, persistent AKI was present in 25 (30.5%) and transient AKI in 57 (69.5%); (2) primary outcome and all-cause death occurred more frequently in patients with persistent AKI and transient AKI than in those with non-AKI, and persistent AKI, but not transient AKI, was an independent predictor of primary outcome; (3) age > 75 years, EF < 40%, and higher maximum CKMB level were independent predictors of persistent AKI.
Contrast-induced nephropathy (CIN) is the main cause of renal dysfunction after PCI and is associated with increased long-term mortality and MACEs [11]. CIN is generally considered transient, with SCr levels typically reaching a peak within a few days and returning to baseline within 2 weeks in most cases [6]. However, some patients with CIN develop persistent increase in SCr levels.
Several studies have reported the incidence and prognostic impact of persistent and transient renal dysfunction after elective [12, 13] and emergency [14–17] PCIs. The time interval for assessing persistent or transient renal dysfunction differed among studies. Some studies assessed persistent or transient renal dysfunction at short time intervals (2 weeks [16] or at discharge [15–17]) from baseline, whereas others assessed long-term interval (1 [14], 3 [12], or 12 months [13]). Some patients, classified as having early persistent renal dysfunction, may have later improved their renal function. Therefore, we assessed persistent or transient renal dysfunction at long-term interval (1 month) from baseline. Despite the time intervals and definition for assessing persistent renal dysfunction among studies, the incidence of persistent renal dysfunction among patients with AKI was approximately 20–60%, which is similar to our result (30.5%).
In previous studies targeting patients who underwent elective PCI, Maioli et al.[12] reported that both persistent and transient renal dysfunctions were independently associated with long-term mortality and MACEs, whereas Abe et al. [13] reported that only persistent renal dysfunction was independently associated with increased long-term mortality. In previous studies targeting patients with AMI, Choi et al. [15] reported that both persistent and transient renal dysfunction were independently associated with long-term mortality, whereas Kurogi et al. [16] reported that persistent renal dysfunction, but not transient renal dysfunction, was independently associated with both long-term mortality and worse clinical outcomes. In the recent large-scale substudy [17] from the MATRIX-Access (Minimizing Adverse Haemorrhagic Events by Transradial Access Site and Systemic Implementation of Angiox) trial, with a study population of 8,201 patients who underwent catheter procedure for acute coronary syndrome (ACS), Landi et al. reported that in-hospital persistent but not transient AKI was independently associated with 1-year MACEs and mortality. The present study demonstrated that persistent renal dysfunction, but not transient renal dysfunction, was independently associated with poor long-term clinical outcomes. These studies, including the present one, consistently suggest that persistent renal dysfunction is associated with worse clinical outcomes. However, the effect of transient renal dysfunction on long-term clinical outcomes differs among studies. Nevertheless, the reversibility of renal dysfunction after AKI development has significant implications for the long-term follow-up of patients who undergo PCI.
Although several risk scores are available as predictors of CIN after cardiac catheterization procedures [18], little is known about the predictors of persistent renal dysfunction. Some studies [19] have investigated the predictors of persistent renal dysfunction and reported that the Mehran risk score [12, 20] and contrast volume/baseline eGFR ratio [16] are useful for predicting persistent renal dysfunction. A recent study [21] reported that the preprocedural N-terminal pro-B-type natriuretic peptide (NT-proBNP) level is useful for predicting persistent renal dysfunction. NT-proBNP reflects impaired cardiac output and increased inflammation [22], which plays an important role in the development of persistent renal dysfunction. The present study demonstrated that age > 75 years, EF < 40%, and higher maximum CK-MB levels were strongly associated with the development of persistent renal dysfunction. Once AMI develops, cardiac function rapidly declines and cardiac damage is sustained. Subsequently, renal hypoperfusion following impaired cardiac output and systemic inflammatory response due to ischemic injury and myocardial necrosis may play important roles in the development of persistent renal dysfunction. Therefore, the assessment of cardiac function and the extent of myocardial necrosis after the onset of AMI might be useful for predicting the development of persistent renal dysfunction. Early clinical follow-up, careful management, and close monitoring of renal function may improve long-term clinical outcomes in patients at high risk of developing persistent renal dysfunction after AKI.
Limitations
This study had several limitations. First, this was a single-center, retrospective observational study. Second, pharmacological treatments ( diuretics, ACE, ARB, and ARNI) and the procedure and examination using contrast media (staged PCI and contrast-enhanced computed tomography) after PCI, which might have influenced the worsening of renal function, were not included in the analysis. Third, we included only three variables to investigate the independent predictors of persistent AKI in the multivariate logistic regression analysis because of the small number of patients with persistent AKI. Fourth, the sample size was small and the present findings were considered exploratory in nature. Therefore, a large-scale prospective cohort study is required to verify our results.
To conclude, in patients who underwent emergency PCI for AMI, persistent AKI was independently associated with worse clinical outcomes, and advanced age, low cardiac function, and greater myocardial necrosis were predictors of persistent AKI.