According to the guidelines and experts’ opinion, chronic kidney disease can be diagnosed
when estimated glomerular filtration rate (eGFR) is lower than 60 ml/min/1.73 m2 and
such a filtration rate lasts for more than 3 months. Impaired kidney function accelerates
the progress of atherosclerosis, significantly increases the risk of adverse cardiovascular
events and worsens prognosis in patients with cardiac diseases. This risk increases
in patients with slightly decreased renal function but increases drastically in patients
on regular dialysis [1–3].
According to epidemiological data, the rate of chronic kidney disease is growing steadily.
About 11% of the population in the United States and Australia have eGFR < 60 ml/min/1.73
m2. In Poland, 10–13% of the general population suffer from chronic kidney disease
[4–7].
Among the patients hospitalized due to coronary artery disease (CAD), 5–7% are diagnosed
with left main disease (LMD), the most severe form of CAD. Patients with LMD require
urgent revascularization, either a coronary artery bypass graft (CABG) operation or
percutaneous coronary intervention (PCI) [8]. Presence of chronic kidney disease in
these patients may increase the risk of complications and mortality connected with
cardiac operation. After coronary angiography and PCI contrast-induced acute kidney
injury (CI-AKI) is more frequently observed. It was also observed that in-hospital
and late mortality are higher in patients with CI-AKI [9, 10]. Cardiac operation in
the group with chronic kidney disease correlates with higher mortality and higher
risk of acute kidney injury which requires dialysis [11].
All popular surgical scores take into account serum concentration of creatinine as
a factor influencing operative risk. Nevertheless, the correlation between concentration
of creatinine and eGFR is not linear. Patients with impaired renal function may have
normal creatinine concentration in serum. Estimated glomerular filtration rate is
crucial in precise assessment of kidney function, especially in high cardiovascular
risk patients such as individuals with LMD treated with CABG [12].
The aim of the study was to assess the prevalence of chronic kidney disease evaluated
by eGFR in patients with LMD and its impact on 30-day prognosis after CABG.
During 2 years (2006–2008) 5000 patients underwent coronary angiography in the Department
of Invasive Cardiology in Bialystok, Poland. We investigated 257 consecutive patients
with significant LMD. Left main disease was recognized when the lumen of coronary
artery disease was < 50%. The majority of the group was treated invasively. One hundred
and seventy-two (67%) of the patients underwent CABG, 19 (7%) underwent PCI without
left main stem protection, 30 (12%) of the group had CABG previously. The remaining
36 (14%) persons were treated conservatively.
The study inclusion criteria were 1) confirmed left main coronary artery stenosis,
2) informed consent obtained from each patient. The study protocol conformed to the
ethical guidelines of the 1975 Declaration of Helsinki and was approved by the local
ethics committee. The exclusion criterion was life-limiting non-cardiac disease. No
upper age limit was used.
Coronary angiography was performed by injection of contrast medium (low osmolarity,
low viscosity) via 6 Fr catheters after 200 µg of intracoronary glyceryl trinitrate
(ICGTN), filmed at 12.5 frames/s. The procedure was done via the radial or femoral
route by the standard Judkins technique. Contrast flow through the epicardial vessel
was graded with the standard Thrombolysis In Myocardial Infarction trial (TIMI trial)
flow scale of 0 to 3. All angiograms were analysed by 2 observers blinded to clinical
and echocardiographic results.
Eventually we enrolled 163 patients with LMD treated with CABG and with known body
mass. We used the Cockcroft-Gault (C-G) formula to assess creatinine clearance [13]
and modified Modification of Diet in Renal Disease (MDRD) [14] and Chronic Kidney
Disease Epidemiology Collaboration (CKD-EPI) equations to calculate eGFR [15]. We
also evaluated creatinine clearance according to the Cockcroft-Gault formula using
calculated lean body mass.
The patients were divided into 2 groups according to eGFR estimated by the MDRD formula:
with eGFR < 60 ml/min/1.73 m2 and with eGFR ≥ 60 ml/min/1.73 m2.
Follow-up was done for 161 patients treated with CABG 30 days after the procedure.
We gathered information either from the patients or from their families by telephone
contact. Missing information was obtained from the Polish population registry (Ministry
of the Interior and Administration) in Bialystok, Poland.
Complications after CABG were assessed in 161 patients operated on in the Department
of Cardiac Surgery of the Medical University of Bialystok, Poland. Only 2 patients
underwent operations in other cardiac centres. We analysed perioperative mortality,
mortality after the procedure and the following complications: stroke, pneumonia or
pleuritis, atrial fibrillation, cardiac tamponade, reoperation due to bleeding or
low cardiac output, difficulties with healing of wounds after sternotomy and saphenectomy
and dehiscence of the sternum.
The prognosis was assessed by 5 scores of cardiac surgical risk: EuroSCORE (numerical
and logistic model), Parsonnet's score, Cleveland score and the Polish Score of Surgical
Risk [16–20].
The patients were treated with the following drugs: acetylsalicylic acid, β-blockers,
angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, statins,
unfractionated heparin or low molecular weight heparin.
The results were analysed using statistical methods from the GRETL (Gnu Regression,
Econometrics and Time-series Library) set and Statistica 10. Differences in means
of continuous variables were compared using Student's t test or the Mann-Whitney U
test. Additional analysis of correlations between non-categorical variables was performed
using Pearson or Spearman tests, where applicable. Multivariate logistic regression
was used to test associations between variables (age, sex, diabetes, body mass index
(BMI), acute coronary syndrome, ejection fraction, glycaemia, cholesterol fractions,
eGFR assessed by various methods and others) and outcomes. Data are expressed as means
and 95% confidence intervals (95% CI). Relative frequencies are used to present categorical
variables. These variables were assessed with the χ2 test. A p value of less than
0.05 was considered as statistically significant.
Values of eGFR/creatinine clearance were calculated according to three different formulae
and also according to the Cockcroft-Gault formula taking into account lean body mass.
The results are shown in Figure 1.
Figure 1
Distribution of eGFR/creatinine clearance values according to four different formulae
used for calculations (n = 163 patients)
There were 42 (26%) patients with eGFR < 60 ml/min/1.73 m2 and 141 (74%) persons with
eGFR ≥ 60 ml/min/1.73 m2 according to the MDRD equation. The patients with lower eGFR
were older. Women made up over half of the group (54.8%). Patients with eGFR < 60
ml/min/1.73 m2 had lower left ventricular ejection fraction. There were fewer smokers
in this group but more patients with diabetes. More patients with LMD and eGFR < 60
ml/min/1.73 m2 than in the other group were hospitalized due to acute coronary syndromes
(Table I). Higher surgical risk was assessed in the group with impaired kidney function
according to all cardiac surgical scores used by us (Table I).
Table I
Clinical, laboratory and angiographic characteristics of patients (n = 163)
Parameter
Patients with eGFR < 60 ml/min/1.73 m2
N = 42% or mean (95% CI)
Patients with eGFR ≥ 60 ml/min/1.73 m2
N = 121 % or mean (95% CI)
Value of p
Age [years]
71.64 (69.5–73.7)
63.69 (61.8–65.6)
< 0.001
Male sex
45.2
81.0
< 0.001
Body mass index (BMI) [kg/m2]
30.1 (28.6–31.7)
27.4 (26.7–28.0)
0.0015
Stable coronary artery disease
28.6
49.6
0.02
Acute coronary syndrome
71.4
50.4
0.02
Left ventricular ejection fraction (%)
47.98 (44.3–51.6)
52.5 (50.6–54.3)
0.025
Diabetes
50.0
16.5
< 0.001
History of hypertension
76.2
77.7
0.842
Hyperlipidaemia
54.8
70.2
0.067
Smoking
26.8
65.8
< 0.001
Family history of CAD
43.9
34.2
0.267
Previous myocardial infarction
52.4
38.0
0.104
Left main coronary artery disease (LMD) (%)
71.3 (65.9–76.7)
70.1 (67.5–72.8)
0.689
Location of stenosis:
Proximal segment
14.3
17.4
0.642
Middle segment
2.4
1.7
0.773
Distal segment
64.3
62.8
0.862
Whole length of main stem
19.0
18.2
0.908
Medium number of coronary arteries with significant stenosis
3.67 (3.46–3.87)
3.31 (3.15–3.48)
0.02
Number of coronary arteries with significant stenosis apart from LMS:
0
2.4
5.0
0.476
1
2.4
15.7
0.023
2
21.4
22.3
0.904
≥ 3
73.8
57.0
0.054
Parsonnet's scale
7.81 (6.55–9.06)
4.49 (3.85–5.12)
< 0.001
Cleveland scale
3.0 (2.18–3.82)
1.72 (1.34–2.10)
0.004
Polish Operation Risk Scale
8.86 (7.97–9.75)
5.57 (4.94–6.20)
< 0.001
EuroSCORE numeric
6.69 (5.70–7.68)
3.9 (3.38–4.42)
< 0.001
EuroSCORE logistic
9.65 (6.29–13.02)
4.09 (3.31–4.88)
0.001
Haemoglobin [mg/dl]
13.4 (12.9–13.8)
14.1 (13.9–14.3)
0.003
Erythrocytes [m/µl]
4.36 (4.23–4.49)
4.60 (4.52–4.68)
0.002
Haematocrit (%)
39.1 (37.9–40.3)
41.4 (40.8–42.1)
< 0.001
Leukocytes [thousands/µl]
7.72 (7.09–8.35)
7.94 (7.53–8.36)
0.559
Platelets [thousands/µl]
236 (211–262)
223 (210–235)
0.348
Fibrinogen [mg/dl]
421 (385–456)
385 (367–404)
0.064
Creatinine [mg/dl]
1.35 (1.28–1.43)
0.98 (0.95–1.00)
< 0.001
Total cholesterol [mg/dl]
168.8 (154.3–183.4)
171.7 (164.1–179.3)
0.691
LDL (low-density lipoprotein) cholesterol [mg/dl]
93.9 (80.9–106.9)
102.3 (96.0–108.5)
0.202
HDL (high-density lipoprotein) cholesterol [mg/dl]
45.2 (40.6–49.8)
44.1 (42.0–46.1)
0.622
Triglycerides [mg/dl]
148.6 (123.5–173.7)
125.9 (113.4–138.5)
0.07
Glycaemia on admission [mg%]
124.6 (105.5–143.7)
108.6 (103.5–113.7)
0.153
In the group with eGFR < 60 ml/min/1.73 m2 we found significantly lower haemoglobin
concentration (Table I). Kidney function also influenced the type of operations. The
patients with lower eGFR were more frequently operated on with off-pump cardiopulmonary
bypass (Table II). This group also needed a valve operation more often than the other
group.
Table II
Data on cardiac surgery (n = 161)
Parameter
Patients with eGFR < 60 ml/min/1.73 m2
N = 42% or mean (95% CI)
Patients with eGFR ≥ 60 ml/min/1.73 m2
N = 119% or mean (95% CI)
Value of p
Coronary artery bypass graft surgery (CABG)
90.5
69.7
0.007
Off-pump cardiopulmonary bypass (OPCAB)
9.5
30.3
0.007
Number of bypass grafts without jump grafts
2.71 (2.50–2.92)
2.57 (2.45–2.69)
0.244
Number of bypass grafts with jump grafts
3.52 (3.17–3.88)
3.19 (3.03–3.36)
0.086
Number of venous bypass grafts
2.0 (1.77–2.23)
1.76 (1.64–1.89)
0.062
Bypass graft LIMA-LAD
73.8
86.5
0.058
Bypass graft Ao-LAD
28.6
16.8
0.099
Bypass graft Ao-Cx/MB
93
83.2
0.118
Bypass graft to RCA
76.2
58
0.035
Arterial bypass graft Cx/MB
2.4
8.4
0.185
Arterial bypass graft to RCA
2.4
1.7
0.774
CABG and valve operation
14.3
4.2
0.026
Left ventricular operations
7.1
2.5
0.174
LIMA – left internal mammary artery, LAD – left anterior descending coronary artery,
Ao – aorta, Cx – circumflex coronary artery, MB – marginal branch, RCA – right coronary
artery.
The patients with eGFR < 60 ml/min/1.73 m2 had significantly more complications with
wound healing on 30-day follow-up (p = 0.004). There were no significant differences
in 7-day or 30-day mortality and complications such as reoperation due to bleeding
or low cardiac output (Table III).
Table III
Complications and mortality after CABG (n = 161)
Parameter
Patients with eGFR < 60 ml/min/1.73 m2
N = 42
Patients with eGFR ≥ 60 ml/min/1.73 m2
N = 119
Value of p
Mortality:
11.9
4.2
0.075
7-day mortality (0–7 days)
7.1
3.4
0.313
30-day mortality (8–30 days)
4.8
1.7
0.269
Complications with wound healing
35.7
15.1
0.004
Sternum dehiscence
16.7
6.7
0.055
Atrial fibrillation
0
3.4
0.314
Pneumonia and pleuritis
4.8
10.1
0.295
Reoperation due to bleeding
4.8
10.1
0.295
Reoperation due to low cardiac output
0
1.7
0.567
Cardiac tamponade
4.8
0
0.058
Stroke
0
1.7
0.567
On multivariate analysis, complications after bypass surgery were significantly more
frequent in women (OR = 0.34; 95% CI: 0.05–1.68; p = 0.035), patients with diabetes
(OR = 5.02; 95% CI: 0.47–2.75, p = 0.005), with high BMI (OR = 1.14; 95% CI: 0.03–0.22;
p = 0.007), low concentrations of HDL cholesterol (OR = 0.93; 95% CI: 0.12–0.018;
p = 0.009) and low eGFR (OR = 0.95; 95% CI: 0.07–0.005; p = 0.026).
In multivariate logistic regression, the following parameters correlated with death
on the 30-day follow-up: age (OR = 1.21; 95% CI: 0.008–0.38, p = 0.04), high glycaemia
on admission (OR = 1.02; 95% CI: 0.003–0.038; p = 0.018) and low left ventricular
ejection fraction (OR = 1.10; 95% CI: 0.03–0.16; p = 0.003).
Impairment of kidney function with eGFR < 60 ml/min/1.73 m2 is a well-established
risk factor of worse prognosis in patients treated with CABG and PCI.
Patients with LMD have poor prognosis. They usually need urgent revascularization.
The treatment of choice is CABG [21, 22]. As the procedure is either urgent or accelerated,
there is a need for quick assessment of cardiosurgical risk. Reliable risk evaluation
may increase the chances of survival.
In our study we investigated the degree of renal impairment in patients with LMD treated
with CABG. Kidney function was assessed using eGFR/creatinine clearance according
to three different formulae.
Distribution of eGFR evaluated by MDRD and CKD-EPI was very similar. We observed only
a 3% difference between the number of patients in stage II and III of chronic kidney
disease in favour of stage II according to the MDRD equation, and in favour of stage
III according to the CKD-EPI equation. Similar distribution of eGFR according to MDRD
was found by Cooper et al. [23] among patients treated with CABG. The distribution
was as follows: 26% of patients with eGFR < 60 ml/min/1.73 m2, 51% in stage II of
chronic kidney disease, 22% with eGFR ≥ 60 ml/min/1.73 m2 and 1% on dialysis.
We achieved slightly different percentage values in the distribution of creatinine
clearance according to the Cockcroft-Gault formula. Although the number of patients
in stage III of chronic kidney disease was comparable to the number of patients classified
according to MDRD and CKD-EPI, fewer patients were found in stage II. The highest
percentage (25%) of patients with eGFR > 90 ml/min/1.73 m2 was observed when calculations
were made using the Cockcroft-Gault formula.
Results achieved by the Cockcroft-Gault formula were overestimated due to excessive
body weight of the patients. That is why we did our calculations once more according
to the Cockcroft-Gault formula, using lean body mass. Then eGFR < 60 ml/min/1.73 m2
was found in 51% of the patients, including 6% in stage IV.
According to Szummer et al. [24], the largest difference between the Cockcroft-Gault
and MDRD estimations was seen when patients were divided according to gender, age,
and weight, as the C-G formula estimated a lower GFR in women, the elderly, and those
with low body weight. In the Szummer et al. study [24], C-G had a stronger association
with 1-year mortality than did the MDRD equation, especially once a receiver operating
characteristic analysis was performed.
Corsonello et al. [25] found that GFR adds to predictors of mortality in an elderly
population discharged from an acute care medical ward, and that the GFR < 30 ml/min/1.73
m2 cut-off marks the highest risk when computed by the C-G formula. This may be attributed
to the fact that the C-G formula, as it is based on the GFR, decreases noticeably
for extremely low weight, and to some extent accounts for the effects of malnutrition.
The fact that the C-G formula tends to give lower creatinine clearance estimations
in those with low body weight largely explains why it is also better at predicting
mortality.
Similar discrepancies in estimating kidney function using the Cockcroft-Gault equation
in comparison to MDRD and CKD-EPI formulae were observed Malyszko et al. [26].
In our further analysis we divided our study population with LMD treated with CABG
into 2 groups, those with eGFR < 60 ml/min/1.73 m2 (26%) and those with GFR ≥ 60 ml/min/1.73
m2 (74%), to assess the influence of kidney function on early prognosis.
Similar to the results from other publications, patients with eGFR < ml/min/1.73 m2
were older, had lower left ventricular ejection fraction and more often suffered from
diabetes [23, 27, 28].
In our study we observed higher 30-day mortality in the group with chronic kidney
disease with eGFR ≥ 60 ml/min/1.73 m2 (11.9% vs. 4.2%). Statistical significance was
not achieved, probably due to the small study group. Similarly, higher perioperative
and 30-day mortality in patients with eGFR below 60 ml/min undergoing CABG was reported
in other studied and cardiac surgery registries [23, 29, 30].
Serum creatinine concentration is considered as one of the main risk factors in cardiosurgical
scores (in EuroSCORE > 2.0 mg/dl, in Cleveland score > 1.8 mg/dl and in the Polish
Score of Surgical Risk > 1.2 mg/dl). Parsonnet's score incorporates regular dialysis
as a risk factor. Nevertheless, serum concentration of creatinine may not reflect
actual kidney function. That is why nowadays eGFR is crucial in precise assessment
of kidney filtration [23, 28, 31].
In October 2011 a new logistic model of EuroSCORE II was presented during European
Association for Cardio-Thoracis Surgery (EACTS) in Lisbon. A special calculator for
this score is available on-line. In EuroSCORE II chronic kidney disease is included
as a surgical risk factor, but the ranges of eGFR values are not concordant with National
Kidney Foundation recommendations. The Cockcroft-Gault formula was recommended as
a convenient equation to assess kidney function [32].
In our study we evaluated perioperative mortality risk according to five different
cardiac surgical scores. The risk in patients with chronic kidney disease was increased
according to all scores although serum creatinine concentration, not eGFR values,
was taken into account.
Chronic kidney disease is frequent in patients with LMD treated with CABG, and it
is associated with more frequent complications with wound healing in 30-day follow-up.
Although we observed higher 30-day mortality in the group with chronic kidney disease,
statistical significance was not achieved, probably due to the small study group.
Diagnosis of LMD in patients with lower eGFR is more often established during hospitalizations
due to acute coronary syndromes than in patients with stable angina. Patients with
chronic kidney disease are more frequently operated on with off-pump cardiopulmonary
bypass. However, despite the limitations, we shed new light on the importance of estimating
GFR as more precise than creatinine, and stressed its possible role as a new predictive
factor for complications in this particular population.
The novelty of this study is that it concerns ‘real life’ patients undergoing CABG.
In addition, we analysed perioperative mortality, mortality after the procedure and
the most common complications and assessed the prognosis using 5 different scores.
Moreover, we paid particular attention to kidney function expressed as either eGFR
by MDRD or CKD-EPI or creatinine clearance by the Cockcroft-Gault formula with correction
for lean body mass. We stressed the role of estimating kidney function and using various
scores for prognosis in predicting outcomes in this very vulnerable population of
patients studied.
Our study is a retrospective analysis. We included consecutive patients with few exclusion
criteria, resulting in a heterogeneous population. Our group consisted of both patients
with LMD and stable angina and patients with LMD and acute coronary syndromes. We
studied only Caucasians; therefore we could generalize our data to the European population.