Abstract
Background
Some prior studies have suggested that the time to cardiac surgery after cardiac catheterization is inversely related to post-operative acute kidney injury (AKI). However, these studies because of small number of patients were unable to adequately account for patient case-mix and included those undergoing either elective or urgent surgery.
Methods and Results
We examined data on 2441 consecutive patients undergoing elective coronary artery bypass surgery (CABG) after cardiac catheterization. The association of post-CABG AKI (defined as increase in post-CABG serum creatinine ≥ 50% above baseline and/or the need for new dialysis) and time between cardiac catheterization and CABG was evaluated using multivariable logistic regression modeling. AKI occurred in 17.1% of CABG patients. The risk of AKI was highest in patients in whom CABG was performed ≤ 1 day of cardiac catheterization (adjusted mean rates [95% CI] 24.0% [18.0%, 30.9%], 18.4% [14.8%, 22.5%], 17.3% [13.3%, 21.9%], 16.4% [12.6%, 20.8%], and 15.8% [13.7%, 18.0%] for days ≤ 1, 2, 3, 4 and ≥ 5, respectively; p = 0.019 for test of trend). Post-CABG AKI was associated with increased risk of long-term death (HR 1.268, 95% CI 1.093–1.471).
Conclusions
The risk of post-CABG AKI was inversely and modestly related to the time between cardiac catheterization and CABG with highest incidence in those operated ≤ 1 day of cardiac catheterization despite their lower risk profile. Whether delaying elective CABG > 24 hours of exposure to contrast agents (when feasible) has the potential for decreasing post-CABG AKI remains to be evaluated in future studies.
Keywords: Coronary artery bypass surgery, acute kidney injury, risk, outcomes
INTRODUCTION
Acute Kidney Injury (AKI) after coronary artery bypass graft surgery (CABG) remains an important adverse event and has been shown to be associated with higher short-term morbidity and mortality and greater resource utilization [1–6]. Many studies have evaluated the risk factors for AKI and need for dialysis after cardiac surgery and have allowed identification of those at risk for this adverse event after this procedure [1,2,5,7]. Cardiac surgery ≤ 1 day of cardiac catheterization has been shown to be associated with increased risk of post-procedural AKI by some [8–11] but not by other studies [12]. However, these studies because of small number of patients were unable to adequately account for patient case-mix and/or included those undergoing elective as well as urgent CABG. Additionally, none of these studies provided any insights into whether outcomes of patients with AKI varied in relation to this time interval.
Accordingly, the goal of this investigation was to investigate the association of the incidence of post-CABG AKI with the time interval between diagnostic angiography and subsequent CABG. We hypothesized that shorter time interval between diagnostic angiography and cardiac surgery will be associated with increased incidence of AKI following CABG and that the strength of the association between post-CABG AKI and short- and long-term mortality may vary according to the time intervals between cardiac catheterization and CABG.
METHODS
Patient population
Using the Duke Cardiovascular Disease Databank [13–15] we identified patients who underwent elective CABG at Duke University Medical Center between January 1, 1995 and June 30, 2008. We excluded patients with prior dialysis, those undergoing urgent, emergent or salvage CABG, those undergoing other cardiac surgery besides CABG, those in whom the time interval between cardiac catheterization and CABG was > 30 days (as contrast use during preceding cardiac catheterization was unlikely to have a deleterious effect on the kidneys at this point), and those who were referred to Duke for CABG but had cardiac catheterization at other institutions. A total of 2441 patients met the study criteria and formed the basis of this analysis.
Cardiac catheterization and CABG were performed in standard manner and day of elective surgery was decided by cardiac surgeons. Routine pre-cardiac catheterization protocol at our institution include the use of intravenous normal saline, avoidance of nephrotoxic drugs, limiting of volume of contrast used and the non-ionic contrast and use of N-acetyl cysteine for patients with serum creatinine ≤ 1.5 mg/dl.
Definitions and follow-up
Acute renal failure was defined asan increase in post-CABG peak creatinine ≥ 50% above baseline, or need for new dialysis [16]. Hypertension, diabetes mellitus, dyslipidemia, peripheral vascular disease, and presenting heart failure were ascertained from that reported as present or absent on the data collection form. After their index CABG, patients were followed at 6 months, 1 year, and annually thereafter for mortality status and other adverse events by telephone contact, mailed questionnaire, and National Death Index search. Mortality (defined as all cause death) was ascertained from the time of index hospitalization. Information from clinic visits and re-hospitalizations was also evaluated to ascertain follow-up and endpoint determination. The methods used by the Cardiovascular Databank have been described previously [13–15]. Considering all time intervals and all patients, follow-up was 98.4% complete.
Statistical analyses
A total of 2441 patients formed the basis of this study. We stratified these patients based on their time interval between cardiac catheterization and CABG into those with ≤ 1 day, 2 days, 3 days, 4 days and ≥ 5 days between the two procedures. Summary statistics are presented as frequencies and percentages or as median values (with 25th and 75th percentile). Comparisons between the patients having AKI when operated ≤ 1 day and those operated > 1 day after their cardiac catheterization were made using χ2 test for categorical variables and Wilcoxon two-sample test for continuous variables. Unadjusted rates of AKI were compared across time interval categories usingthe Mantel chi-square trend test. The multivariable association between time interval from catheterization to CABG and risk of AKI was assessed using a non-parsimonious logistic regression model with adjustment for the following characteristics: age, male sex, race, body mass index, diabetes, hypertension, chronic lung disease, cerebrovascular disease, peripheral vascular disease, history of congestive heart failure, history of CABG, history of percutaneous coronary intervention, history of myocardial infarction, cardiogenic shock, number of diseased vessels, left main disease, left ventricular ejection fraction, total contrast volume, non-ionic contrast use, internal mammary artery use, year of surgery, cross-clamp time, pre-CABG serum creatinine and hemoglobin. These model covariates were selected based on clinical judgment and literature and were retained in the model regardless of statistical significance. Continuous variables were modeled asrestricted cubic splineswith 4 data-driven knot locationsto account for possible non-linear regression relationships. Days from catheterizationto CABG was modeled both as an ordinal variable (linear across the categories) and as a set of category (0/1) indicator variables using 0–1 days as the reference group. In addition to reporting odds ratios with 95% confidence intervals, risk-adjusted AKI rates were calculatedby the method of indirect standardization and displayed for each of the 5 time interval categories. For each category, the risk-adjusted AKI rate was calculated by dividing the category-specific observed AKI rate by the category-specific average predicted probability of AKI and then multiplying this ratio by the overall aggregate AKI rate in the study sample. Predicted probabilities for the adjusted AKI rate calculation were based on a separate logistic regression model that included all of the covariates listed above with the exception of days from catheterization to CABG. Confidence intervals for the adjusted AKI rate were calculated based on the binomial distribution by treating the average predicted rate in each category asconstant. As a subsequent sensitivity analysis, we re-estimated the multivariable model after including after including two interaction terms (age × prior CABG and age × baseline creatinine) which were identified from previous risk models [17].
Finally, the association between occurrence of perioperative AKI and long term all-cause mortality was assessed using Cox proportional hazards modelwith adjustment for the following covariates [18]: age, ejection fraction, chronic lung disease, diabetes, history of congestive heart failure, peripheral vascular disease, cerebrovascular disease, body mass index, dyslipidemia, left main disease, use of internal mammary artery graft, pre-procedure creatinine level and time interval between cardiac catheterization and CABG. This model was then re-estimated after including the interaction of the time interval from cardiac catheterization to CABG × AKI in order to assess whether the association of post-operative AKI was constant across the time intervals of interest. P values of < 0.05 were considered significant. The software SAS version 8.2 (SAS Institute, Cary, North Carolina) was utilized for all analyses.
RESULTS
Patients and baseline clinical and angiographic characteristics
Of the 2441 patients undergoing CABG who were eligible for this study, AKI occurred in 417 subjects (17.1%). Median follow up for the entire group was 9.2 years (IQR 5.3, 11.9 years). Table 1 shows the distributions of baseline clinical and angiographic features of patients withpost-CABG AKI stratified by the time interval between cardiac catheterization and CABG. Compared with patients who had CABG performed > 1 day, those having CABG performed ≤ 1 day, were younger, more frequently male and had fewer comorbidities including diabetes mellitus, peripheral vascular disease, prior CABG, chronic obstructive airway disease, and presenting heart failure. The volume of contrast used was similar whereas the use of non-ioniccontrast was lower in the early CABG cohort. Baseline serum creatinine was lower and hemoglobin was higher in the early CABG group compared with those who had CABG > 1 day after cardiac catheterization. Angiographic features such as presence of 2 or more vessel coronary artery disease, left ventricular ejection fraction and surgical features such as number of bypass graft use, on-pump surgery and the circulatory and cross-clamp time were similar in the different categories whereas the use of IMA conduit was higher in the early CABG group.
Table 1.
Baseline clinical and angiographic features.
| Characteristic | Overall | Day 0–1 | Day 2 | Day 3 | Day 4 | Day ≥ 5 |
|---|---|---|---|---|---|---|
| Number of patients | 2441 (100%) | 206 (8.4%) | 450 (18.4%) | 372 (15.2%) | 366 (15.0) | 1047 (43.0%) |
| Age, (years)‡ | 66 (57, 73) | 64 (56, 72) | 66 (59, 73) | 64 (56, 72) | 66 (58, 73) | 66 (57, 73) |
| Female sex† | 721 (29.5%) | 48 (23.3%) | 126 (28.0%) | 130 (35.0%) | 109 (29.8) | 308 (29.4) |
| White race | 2002 (82.3%) | 171 (83.8%) | 378 (84.2%) | 307 (82.5%) | 302 (82.5%) | 844 (81.1%) |
| Body mass index, (kg/m2) | 27.4 (24, 31) | 27.2 (25, 30) | 27.4 (24, 31) | 27.8 (24, 31) | 26.8 (24, 30) | 27.5 (24, 31) |
| Hypertension | 1816 (74.4%) | 149 (72.3%) | 341 (75.8%) | 269 (72.3%) | 261 (71.3%) | 796 (76.0%) |
| Diabetes mellitus† | 815 (33.4%) | 54 (26.2%) | 148 (32.9%) | 115 (30.9%) | 115 (31.4%) | 383 (36.6%) |
| Current/past smoker | 1617 (66.2%) | 140 (68.0%) | 295 (65.6%) | 245 (65.9%) | 250 (68.3%) | 687 (65.6%) |
| Dyslipidemia** | 1686 (69.1%) | 140 (68.0%) | 309 (68.7%) | 260 (69.9%) | 246 (67.2%) | 731 (69.8%) |
| Prior myocardial infarction | 1179 (48.3%) | 90 (43.4%) | 238 (47.1%) | 203 (54.6%) | 190 (51.9%) | 484 (46.2%) |
| Chronic lung disease | 298 (12.2%) | 17 (8.3%) | 57 (12.7%) | 34 (9.1%) | 49 (13.4%) | 141 (13.5%) |
| Prior PCI | 473 (19.4%) | 38 (18.5%) | 91 (20.2%) | 71 (19.1%) | 66 (18.3%) | 207 (19.8%) |
| Prior CABG† | 149 (6.1%) | 6 (2.9%) | 14 (3.1%) | 21 (5.7%) | 18 (4.9%) | 90 (8.6%) |
| Prior congestive heart failure† | 809 (33.1%) | 55 (26.7%) | 122 (27.1%) | 91 (24.5%) | 96 (26.2%) | 445 (42.5%) |
| Cerebrovascular disease | 365 (15.0%) | 27 (13.1%) | 66 (14.7%) | 54 (14.5%) | 48 (13.1%) | 170 (16.2%) |
| Peripheral arterial disease† | 424 (17.4%) | 23 (11.2%) | 69 (15.3%) | 53 (14.3%) | 69 (18.9%) | 210 (20.1%) |
| Presenting characteristics | ||||||
| NYHA class ≥ 3 | 506 (20.7%) | 35 (17.0%) | 73 (16.2%) | 50 (13.4%) | 56 (15.3%) | 292 (27.9%) |
| Cardiogenic shock | 41 (1.7%) | 3 (1.5%) | 13 (2.9%) | 6 (1.6%) | 2 (0.6%) | 17 (1.6%) |
| Angiographic features | ||||||
| LVEF (%)‡ | 54 (43, 65) | 55 (45, 64) | 55 (44, 65) | 55 (44, 65) | 54 (44, 66) | 52 (40, 64) |
| Diseased coronary arteries ≥ 2 | 2230 (91.4%) | 189 (91.7%) | 425 (94.4%) | 346 (93.0%) | 334 (91.3%) | 936 (89.4%) |
| Left main disease (> 50%) | 730 (29.9%) | 71 (34.5%) | 137 (30.4%) | 111 (29.8%) | 122 (33.3%) | 289 (27.6%) |
| Non-ionic contrast† | 2052 (84.1%) | 156 (75.7%) | 371 (82.4%) | 320 (86.0%) | 314 (85.8%) | 891 (85.1%) |
| Laboratory data | ||||||
| Hemoglobin, (gm/dL)†‡ | 13 (12, 14) | 13 (12, 14) | 13 (12, 14) | 13 (11, 14) | 13 (12, 14) | 13 (12, 14) |
| Preoperative serumcreatinine mean (SD), (mg/dL)† | 1.18 (0.52) | 1.08 (0.25) | 1.14 (0.44) | 1.13 (0.41) | 1.14 (0.47) | 1.25 (0.63) |
| Surgical data | ||||||
| On-pump surgery | 2364 (96.9%) | 203 (98.5%) | 438 (97.3%) | 366 (97.8%) | 358 (97.8%) | 999 (95.2%) |
| IMA use† | 2199 (90.1%) | 196 (95.2) | 427 (94.9) | 336 (90.3) | 334 (91.3) | 906 (86.5) |
| Number of grafts ≥ 2 | 2227 (91.3%) | 191 (92.7%) | 427 (94.9%) | 345 (92.7%) | 339 (92.6%) | 925 (88.3%) |
| Cross-clamp time‡ | 59 (42, 80) | 57 (42, 80) | 53 (39, 74) | 57 (41, 74) | 59 (44, 77) | 63 (43, 87) |
| Perfusion time‡ | 13 (12, 14) | 13 (12, 14) | 104 (85, 135) | 108 (86, 137) | 113 (89, 139) | 117 (92, 150) |
For significant difference (p < 0.05) in AKI day 0–1 versus AKI on other days.
Variables presented as median (25th, 75th).
Abbreviations: AKI = acute kidney injury; CABG = coronary artery bypass grafting;IMA = internal mammary artery; LVEF = left ventricular ejection fraction; NYHA = New York Heart Association; PCI = percutaneous coronary interventions; SD = standard deviation.
Relationship of the Time Interval between Cardiac Catheterization and CABG with post-CABG AKI
The observed rate of AKI was highest when CABG was performed early (unadjusted p value for trend = 0.38). Multivariable logistic regression analyses suggested that the risk of post-CABG AKI was inversely (albeit modestly) associated with the interval between cardiac catheterization and CABG (adjusted OR per each time interval 0.90, 95% CI 0.83–0.98, p = 0.019). The inverse association of time interval between cardiac catheterization and post-CABG AKI persisted even after adding interaction terms for age × prior CABG and age × baseline serum creatinine (OR 0.91, 95% CI 0.83–0.99, p = 0.0253). Figure 1 showsthe observed and adjusted rates (95% CI) whereas Table 2 demonstrates unadjusted and adjusted odds ratios (95% CI) of AKI for patients with different time intervals between cardiac catheterization and CABG. The highest adjusted mean rate (adjusted OR) of post-CABG AKI occurred when the interval was ≤ 1 day.
Figure 1.
Observed (squares) and adjusted rates (diamonds) and 95% confidence intervals of Acute Kidney Injury (AKI) following Coronary Artery Bypass Graft Surgery (CABG). Obs = Observed and Adj = Adjusted.
Table 2.
Unadjusted and adjusted Odds ratio and 95% Confidence Intervals (CIs) for AKI in patients undergoing elective CABG and adjusted Hazard Ratios (HRs) and 95% CIs for long-term mortality in patients with AKI.
| Days from Cardiac Catheterization to CABG | 0–1 | 2 | 3 | 4 | ≥ 5 |
|---|---|---|---|---|---|
| Unadjusted Post-CABG AKI Odds Ratios (referent days ≥ 5) | 1.34 (0.93–1.93) | 1.00 (0.75–1.34) | 0.87 (0.63–1.20) | 0.86 (0.62–1.20) | 1.00 |
| Adjusted Post-CABG AKI Odds Ratios (referent days ≥ 5) | 1.74 (1.13–2.68) | 1.26 (0.91–1.74) | 1.11 (0.77–1.59) | 1.15 (0.80–1.63) | 1.00 |
| Adjusted Post-CABG mortality in patients with AKI (Ref no AKI) HR (95% CI) | 1.27 (1.09, 1.47) | 1.37 (0.92, 2.04) | 1.11 (0.80, 1.53) | 1.13 (0.75, 1.69) | 1.56 (1.10, 2.20) |
:AKI = Acute Kidney Injury; CABG = Coronary artery bypass graft surgery; CI = confidence interval; HR = Hazard ratio.
In-hospital events and long-term mortality [median follow-up 9.2 years (IQR 5.3, 11.9 years)] are shown in Tables 2 and 3. Post-CABG AKI was associated with an increased risk of long-term mortality compared with patients without any AKI (HR 1.27, 95% CI 1.09–1.47; p = 0.0017). In contrast, for the overall study population; the time interval between cardiac catheterization and CABG was not significantly associated with an increased risk of long-term mortality (HR 0.99, 95% CI 0.94–1.04, p = 0.70). For other in-hospital adverse events, there was no apparent increasing or decreasing relationship with the time interval between cardiac catheterization and CABG (Table 3).
Table 3.
In-hospital outcomes and 30-day mortality.
| Event | Overall | Day 0–1 | Day 2 | Day 3 | Day 4 | Day ≥ 5 |
|---|---|---|---|---|---|---|
| Number of patients | 2441 (100%) | 206 (8.4%) | 450 (18.4%) | 372 (15.2%) | 366 (15.0) | 1047 (43.0%) |
| 30-day death | 62 (2.54%) | 4 (1.94%) | 11 (2.44%) | 10 (2.69%) | 5 (1.37%) | 32 (3.06%) |
| Permanent stroke | 36 (1.47%) | 5 (2.43%) | 1 (0.22%) | 7 (1.88%) | 5 (1.37%) | 18 (1.72%) |
| Perioperative MI | 3 (0.12%) | 1 (0.49%) | 1 (0.22%) | 1 (0.27%) | 0 | 0 |
| Prolonged ventilation | 142 (5.82%) | 12 (5.83%) | 29 (6.44%) | 20 (5.38%) | 22 (6.01%) | 59 (5.64%) |
| Pneumonia | 43 (1.76%) | 7 (3.40%) | 6 (1.33%) | 6 (1.61%) | 5 (1.37%) | 19 (1.81%) |
| Any blood product use | 1096 (44.9%) | 91 (44.2%) | 202 (44.9%) | 166 (44.6%) | 153 (41.8%) | 484 (46.2%) |
| Postoperative IABP use | 14 (0.57%) | 1 (0.49%) | 3 (0.67%) | 4 (1.08%) | 2 (0.55%) | 4 (0.38%) |
| Deep sternal wound infection | 24 (0.98%) | 4 (1.94%) | 4 (0.89%) | 1 (0.27%) | 6 (1.64%) | 9 (0.86%) |
| Septicemia | 5 (0.20%) | 1 (0.49%) | 1 (0.22%) | 0 | 2 (0.55%) | 1 (0.10%) |
| Postoperative length of stay, median (25th, 75th), days‡ | 5 (4, 7) | 5 (4, 7) | 5 (4, 6) | 5 (4, 7) | 5 (4, 7) | 5 (4, 8) |
For difference in AKI day 0–1 versus AKI on other days.
Variables presented as median (25th, 75th),. IABP, intra-aortic balloon pump, MI = myocardial infarction.
DISCUSSION
Our study findings
This investigation demonstrates that among patients undergoing elective CABG, the risk of post-procedural AKI was inversely and modestly associated with time between cardiac catheterization and subsequent CABG. After adjusting for numerous covariates, including volume and type of contrast, risk was highest among patients undergoing CABG ≤ 1 day of cardiac catheterization and declined over 5 days. Furthermore, our data suggested that while post-CABG AKI was independently associated with higher long-term mortality, the time interval between cardiac catheterization and subsequent CABG was not associated with long-term death.
Comparison with prior studies
Some prior studies have focused on evaluating the influence of the time interval between cardiac catheterization and CABG (Table 4). Brown et al [12] examined the safety of performing elective valve surgery on the day of cardiac catheterization limited to pressure measurements and only coronary angiography (no left ventriculogram or aortogram). They showed that post-procedural AKI occurred in a small minority (1.8%) with only 2 patients (0.9%) needing renal replacement therapy. They surmised that valve surgery on same day as cardiac catheterization in selected patients was safe and was associated with no significant influence on renal function. Del Duca et al [8] studied patients undergoing elective or urgent cardiac surgery and showed that CABG performed ≤ 5 days of cardiac catheterization was associated with increased risk of AKI compared with those operated later (OR 1.82, 95% CI 1.17–2.84). Patients operated ≤ 1 day of cardiac catheterization had the highest risk (OR 1.70, 95% CI 0.91–3.20 [referent = patients operated > 5 days after cardiac catheterization]). Ranucci et al [9] and Medalion et al [10] demonstrated similar heightened risk when cardiac surgery was performed ≤ 1 day compared with those operated after 1 day [(OR 3.1, 95% CI 1.1–8.8) and (OR 3.7, 95% CI 1.4–8.3), respectively]. Finally, Hennessey et al [11] replicated similar results among patients undergoing valve surgery showing high risk of AKI when the operation was performed ≤ 1 day of cardiac catheterization.
Table 4.
Studies evaluating the relationship of AKI with the time interval between cardiac catheterization and CABG.
| Study (N) | Patient population | Status of procedure | Exclusion criteria | Definition of AKI | AKI (dialysis) incidence | Comparison group in Logistic model |
|---|---|---|---|---|---|---|
| Brown et al (226 patients) [12] | Valve surgery | Elective | serumcreatinine > 1.8 mg/dl, urgent, emergent, salvage | serum creatinine > 2x baseline and total > 2 mg/dl | 1.8% (0.9%) | None |
| Del Duca et al (649 patients) [8] | CABG, valve and other cardiac surgeries | Elective or urgent | Preoperative dialysis, cardiac transplantation, ventricular assist devices, aortic dissection, emergent/salvage surgery | serum creatinine ≥ 25% above baseline | 24% (4.2%) | ≥ 5 vs. > 5 days (OR 1.82, 95% CI 1.17–2.84) |
| Ranucci et al (423 patients) [9] | CABG, valve and other cardiac surgeries | Elective or urgent | Emergent/salvage surgery, preoperative dialysis, congenital heart disease, off pump surgery | serum creatinine > 2x baseline and total > 2 mg/dl | 5.7% (0.5%) | ≤ 1 vs. > 1 day (OR 3.1, 95% CI 1.1–8.8) |
| Medalion B et al (395 patients) [11] | First time CABG | Elective or urgent | Emergent/salvage surgery, preoperative dialysis, off pump surgery | ≥ 25% decrease of creatinine clearance from baseline | 13.6% | ≤ 1 vs. > 1 day (OR 3.7, 95% CI 1.4–8.3) |
| Hennessey et al (1287 patients) (61 with and 136 without AKI matched for comparisons) [12] | Valve surgery | Elective or urgent | Non-valvular cardiac surgery, emergent/salvage surgery | serum creatinine > 2x baseline and total > 2 mg/dl | 6.6% (3.3%) | ≤ 1 versus > 3 days (OR 5.3, 95% CI 1.4–19.0) |
| Mehta et al (present study) (2441 patients) | CABG | Elective | Non-CABG or urgent/emergent/salvage surgeries, preoperative dialysis. | serum creatinine ≥ 50% above baseline | 17.1% (0.9%) | Continuous variable ≤ 1 to ≥ 5 days (OR 0.92, 95% CI 0.85–0.99). |
AKI = Acute Kidney Injury; CABG = coronary artery bypass graft surgery, CI = confidence interval; OR = odds ratio
Our study results are consistent with those of above studies and suggested similar association between post CABG AKI and early cardiac surgery after cardiac catheterization (particularly ≤ 1 day). However, unlike most of the above studies that included relatively smaller number of patients undergoing elective or urgent cardiac surgery, we studied a relatively larger cohort undergoing only elective CABG. Patients undergoing urgent operation are more likely to be sicker with hemodynamic instability and more comorbid conditions that generally mandate immediate operations, biasing those operated earlier to demonstrate higher incidence of AKI. Additionally, we demonstrated that there was a declining trend up to 5 days rather than just an increased risk on ≤ 1 day after cardiac catheterization.
Clinical Implications
Despite the differences in patient population, inclusion and exclusion criteria and the definition of AKI used in previous and our studies, they provide a consistent unifying message-early cardiac surgery (particularly ≤ 1 day) may be associated with ahigher incidence of post-procedural AKI. Thus, postponing cardiac surgery for 24 to 48 hours (when feasible) especially in elective cases may have the potential for minimizing the additive adverse effect of contrast and cardiopulmonary bypass, a hypothesis that remains to be proven in future study. These data should not be viewed as being prohibitive for proceeding with early cardiac surgery in patients in whom delaying surgery may have the potential for greater harm. A clinical decision should be made in those needing early surgery based on the perceived risk of immediate surgery on renal function versus that for ischemic events and its consequences while waiting longer. If early surgery is indeed warranted, all efforts should be directed at minimizing the deleterious effects of contrast and cardiopulmonary bypass on renal tubules. Prevention and treatment of prolonged periods of hypotension, shorter cardiopulmonary bypass time, maintenance of adequate hematocrit and oxygenation during cardiopulmonary bypass and avoidance of nephrotoxic drugs in the perioperative period may help to minimize the risk of AKI in these individuals. Strategies to prevent contrast induced nephropathy [19] should be routinely adapted during angiography and continued in post-operative period with the hope that this may help reduce post-operative AKI in those needing early cardiac surgery following cardiac catheterization.
Limitations
Our study has some limitations. This is a retrospective observational study. Thus, our findings should be regarded as hypothesis generating and inference regarding causality should be made with caution. As with any retrospective study, we could only adjust for variables collected in our database. Thus, days from cardiac catheterization to CABG may be a marker of unmeasured confounding variables rather than being an independent correlate of post-CABG AKI and the influence of any unmeasured confounders on the risk of AKI cannot be ascertained. Furthermore, the number of events in patients undergoing elective CABG was still small for making any definitive conclusions regarding the association of AKI, time interval between cardiac catheterization and CABG with outcomes. Majority of our patients underwent CABG on-pump and our findings should not be extrapolated to those undergoing off-pump CABG, a strategy also commonly employed simultaneously with percutaneous coronary interventions in those undergoing hybrid coronary revascularization/cardiac surgery. Whether or not off-pump compared with on-pump CABG in those undergoing early surgery after cardiac catheterization would helpreduce the incidence of post-CABG AKI remains to be proven in future investigation. We did not collect information regarding strategies used to prevent and/or improve post-CABG AKI that may have influenced patient outcomes. Our results are best applicable to patients undergoing elective isolated CABG.
Conclusions
The current study showed that the risk of post-CABG AKI was inversely, but modestly; related to the time interval between cardiac catheterization and CABG. The highest incidence of post-CABG AKI occurred when CABG was performed ≤ 1 day of cardiac catheterization and then declined over 5 days. This high incidence occurred despite the lower risk profile of patients operated earlier. Whether delaying elective CABG > 24 hours of exposure to contrast agents (when feasible) has the potential for decreasing post-CABG AKI remains to be proven. In addition, whether strategies used to prevent and/or improve post-cardiac catheterization and post-CABG AKI would have the potential forreducing the incidence of AKI among those operated early and would help improve patient outcomes also remain to be studied in future.
Acknowledgments
Funding source: Dr. Patel is funded by NIH grant K23 DK075929.
Footnotes
Conflict of Interest Disclosures: None for all authors.
Disclosure Information: Disclosures none for current paper for all authors. A complete listing of financial disclosure information is available for Dr. Mehta at https://dcri.org/about-us/conflict-of-interest/Mehta-COI.pdf and for Dr. Califf at: https://dcri.org/about-us/conflict-of-interest/Califf-COI_2009.pdf
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