Acute kidney injury after coronary artery bypass grafting and long-term risk of myocardial infarction and death

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Abstract

Background

Acute kidney injury (AKI) after coronary artery bypass grafting (CABG) is associated with early mortality. Its impact on the risk of myocardial infarction (MI) over time and long-term mortality has not been well described.

Methods

We performed a nationwide population-based cohort study in 27,929 patients who underwent a first isolated CABG between 2000 and 2008 in Sweden. Acute kidney injury was divided into three categories based on the absolute increase in postoperative serum creatinine (sCr) concentration compared with the preoperative baseline: stage 1, sCr increase of 0.3 to 0.5 mg/dL; stage 2, sCr increase of > 0.5 to 1.0 mg/dL and stage 3, sCr increase of ≥ 1.0 mg/dL.

Results

The overall incidence of postoperative AKI was 13%, 6.3% met the criterion for stage 1, 4.3% for stage 2 and 2.3% for stage 3. During a mean follow-up of 5.0 years, there were 2119 (7.6%) MIs and 4679 (17%) deaths.

Multivariable adjusted hazard ratios with 95% confidence intervals for MI were 1.35 (1.15 to 1.57), 1.80 (1.53 to 2.13) and 1.63 (1.29 to 2.07), in AKI stages 1, 2 and 3, respectively. The corresponding hazard ratios for all-cause mortality were 1.30 (1.17 to 1.44), 1.65 (1.48 to 1.83) and 2.68 (2.37 to 3.03), respectively.

Conclusions

Our results show that AKI after CABG is associated with an increased long-term risk of MI and death.

Introduction

Coronary artery disease is a global health problem. It is commonly treated by coronary artery bypass grafting (CABG) or percutaneous coronary intervention. Acute kidney injury (AKI) affects 5 to 30% of patients after CABG depending on the classification used and the study population [1]. Recently, several studies have shown that even a small increase in the serum creatinine (sCr) concentration is an independent and important risk factor for postoperative morbidity and mortality in patients undergoing CABG in both short [1], [2], [3] and long terms [4], [5]. A recent study also shows an association between AKI after CABG and long-term risk of heart failure [6].

About 3 to 7% of patients undergoing CABG will suffer a myocardial infarction (MI) within 1 year of surgery [7], [8], [9]. In a previous study on the risk of MI associated with chronic kidney disease (CKD) it was found that 6% of patients with normal renal function had an MI within 5 years [10]. With declining estimated glomerular filtration rate (eGFR) the risk of MI steadily increased. Among patients with eGFR < 30 mL/min/1.73 m [2], 19% experienced an MI within 5 years of CABG [10]. It is well known that patients with CKD have an increased risk of adverse cardiac events [10], [11], but to date, in our knowledge, there have been no studies that have examined whether AKI after CABG is associated with an increased risk of MI in the long term. The aim of this study was to investigate the association between AKI and MI in patients who underwent a primary isolated non-emergent CABG in Sweden between 2000 and 2008.

Section snippets

Study population

All patients undergoing CABG between 2000 and 2008 in Sweden were eligible for this study. The following patients were excluded: those with prior cardiac surgery; CABG performed with one or more additional procedures; MI within 7 days of CABG and missing pre- and/or postoperative creatinine values. Patients who underwent surgery within 24 h of the decision to operate, and patients with preoperative eGFR less than 15 mL/min/1.73 m2 were also excluded. The exclusion criteria and number of patients

Results

A total of 27,927 patients with a mean age of 67 years were included; 21% were women. Thirteen percent of the patients developed AKI, 6.3% stage 1, 4.3% stage 2 and 2.3% stage 3. Before CABG 20% had chronic kidney disease with eGFR < 60 mL/min/1.73 m2, but only 1% had an eGFR between 15 and 30 mL/min/1.73 m2. Patients with AKI were older and more likely to have: a reduced eGFR; a history of MI, stroke, heart failure, or diabetes mellitus; or a low ejection fraction (Table 1).

During a mean follow-up

Discussion

We found that AKI after CABG is associated with elevated risks of MI and death in both short- and long-term perspectives. The majority of studies that have measured survival after CABG-induced AKI have focused on the short term and there are just a few studies on the impact of AKI on long-term survival [4], [18]. The incidence of AKI was found to be 37% in a cohort of 2970 patients without a history of CKD undergoing any cardio-thoracic surgical procedure and discharged alive from hospital by

Conclusion

AKI after CABG is associated with an increased risk of MI and death. This is true even for small increases in sCr after surgery. Patients with AKI after CABG may benefit from more careful monitoring and initiation of secondary preventive measures.

Acknowledgments

We are grateful to the steering committee of SWEDEHEART for making their data available for the purpose of this study.

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