Abstract
Background:
The pathophysiology of coronary slow flow (CSF) has not been clearly identified, although multiple abnormalities including arteritis, endothelial dysfunction, and atherothrombosis have been reported. Several studies have demonstrated that higher serum bilirubin inhibits the inflammation and proliferation of vascular smooth muscle cells; in addition, there is a relationship between serum bilirubin and cardiovascular disease. However, the relationship between bilirubin and CSF is still unknown. In our study, we compared serum bilirubin concentrations between CSF patients and controls.
Methods:
The study included 50 CSF patients (19 male, mean age 65.6 ± 13.7 years) and 30 controls (10 male, mean age 57.86 ± 11.6 years). Concurrent routine biochemical tests and leukocyte count, hemoglobin, hematocrit, and platelet count on whole blood count were performed in patients that underwent a coronary angiogram. These parameters were compared between groups.
Results:
No statistically significant difference was found between the two groups in terms of basic characteristics. Total, direct, and indirect serum bilirubin levels were significantly lower among CSF patients than controls (14.0 ± 12.0 versus 6.15 ± 6.8, 5.6 ± 3.4 versus 2.6 ± 1.7, and 8.4 ± 8.5 versus 3.6 ± 3.4 µmol/l; all p < 0.001, respectively).
Conclusions:
The study revealed a relationship between serum bilirubin and CSF.
Introduction
Coronary slow flow (CSF) is characterized by delayed opacification of coronary arteries in the absence of obstructive coronary artery disease (CAD) in coronary angiography [Doğan et al. 2013].
Several mechanisms have been proposed for the etiology of CSF, including microvascular and endothelial dysfunction, small-vessel disease, diffuse atherosclerosis, and inflammation. However, the etiology is still not clear. Previously it has been shown that there is a significant relationship between inflammatory markers and coronary flow rate [Cin et al. 2003; Kalay et al. 2011].
Bilirubin is an important and potent endogenous antioxidant and anti-inflammatory agent. Several studies have demonstrated a relationship between serum bilirubin levels and cardiovascular disease such as CAD [Minetti et al. 1998; Schwertner et al. 1994; Levinson, 1997].
To our knowledge, no previous study has examined the association between serum bilirubin concentration and CSF. In our study, we investigated the relationship between bilirubin concentration in CSF patients and control subjects.
Methods
Selection of patients
The study group included 50 patients (19 male, mean age 65.6 ± 13.7 years) with isolated CSF without stenotic lesions under visual assessment. The control group consisted of 30 age- and gender-matched subjects (10 male, mean age 49.16 ± 9.2 years) who proved to have normal coronary angiograms.
The indication for coronary angiography was either the presence of typical angina, or positive or equivocal results of noninvasive screening tests for myocardial ischemia in both groups.
Physical examination, medical history of patients, blood biochemistry, and transthoracic echocardiographic examination were evaluated in both groups to exclude systemic diseases. Patients with obstructive CAD (coronary stenotic lesions of >20%), chronic renal failure, chronic liver disorders, chronic lung disease, moderate or severe valvular disease, hypertension, diabetes mellitus, congenital heart disease, left ventricular systolic dysfunction on echocardiography (ejection fraction <50%), anemia, pregnancy, obstructive sleep apnea, hematological disorders, known malignancy, thyroid dysfunction, hypercholesterolemia, electrolyte imbalance, and drug history including anti-gout agents, anti-inflammatory agents (steroidal or nonsteroidal), anti-aggregant or anticoagulant agents, antihistaminic, and any medication that could potentially interfere with the measurement of eosinophil count were excluded from the study. In addition, patients with a recent history of acute infection or high body temperature (>38°C), an inflammatory or allergic disease were excluded from the study.
Patients with a systolic blood pressure ≥140 mmHg and/or a diastolic blood pressure ≥90 mmHg, and those taking antihypertensive drugs were accepted to be hypertensive. Diabetes was defined as a fasting blood glucose level greater than 6.7 mmol/l, or current use of a diet or medication to lower blood glucose. Current cigarette smoking was defined as more than 10 cigarettes/day at the time of diagnosis. All patients signed an informed consent form and the local ethics committee (Bursa Education and Research Hospital) approved the study.
Coronary angiography
Coronary angiograms were carried out using a femoral approach with the Judkins technique without the use of nitroglycerin, adenosine, or a calcium channel blocker. All patients in the study population underwent elective coronary artery angiography using the Siemens Axiom Artis DFC (Siemens Medical Solutions, Erlangen, Germany), following appropriate patient preparation. Coronary angiograms were evaluated with regard to smooth appearance, luminal wall irregularities, epicardial local or diffuse caliber reduction, and stenosis.
Coronary arteries were visualized in at least four views of the left coronary system using six French left coronary catheters, and two views of the right coronary artery using six French right coronary catheters at a rate of 15 fps in the same cardiac catheterization laboratory. Coronary blood flow was measured quantitatively using the thrombolysis in myocardial infarction frame count (TFC). The initial frame count is defined as the frame in which concentrated dye occupies the full width of the proximal coronary artery lumen, touching both borders of the lumen, and forward motion down the artery. The final frame is designated when the leading edge of the contrast column initially arrives at the distal end. The distal end was defined as the distal bifurcation for the left anterior descending (LAD) artery, the distal bifurcation of the segment with the longest total distance for the circumflex artery (CX), and the first branch of the posterolateral artery for the right coronary artery (RCA). The LAD coronary artery is usually longer than the other major coronary arteries; the TFC for this vessel is often higher. To obtain a corrected TFC for the LAD coronary artery, the TFC was divided by 1.7. The mean TFC for each patient and control subject was calculated by adding the TFC for LAD, CX, and RCA and then dividing the obtained value into three. Due to different durations required for normal visualization of coronary arteries, the corrected cutoff values were 36.3 ± 2.6 frames for LAD, 22.3 ± 4.1 frames for CX, and 20.5 ± 3.0 frames for RCA, as has been reported previously in the literature [Gibson et al. 1996]. All participants with a TFC greater than the two standard deviations of the previously published range for the particular vessel were considered to have CSF. Any values obtained above these thresholds in one of three coronary arteries (not all three) were considered to be CSF in our study. Coronary angiograms and TFC were analyzed by two experienced interventional cardiologists blinded to the clinical status and laboratory measurements of the subjects.
Laboratory tests
Biochemical parameters were analyzed spectrophotometrically on an Architect c16000 (Abbott Diagnostics, Lake Forest, IL, USA) autoanalyzer using enzymatic-colorimetric assay.
For whole blood count (hematocrit, hemoglobin, leukocytes, and platelets), the blood samples were collected in tubes with ethylenediaminetetraacetic acid and analyzed on a CELL-DYN 3700 device (Abbott Diagnostics) using impedance and optic scatter method.
Statistical analysis
SPSS 16.0 statistical program (SPSS Inc., Chicago, IL, USA) was used for statistical analysis. All values are given as mean ± standard deviation. Mean values of continuous variables were compared between groups using the Student’s t-test or Mann–Whitney test, according to whether normally distributed or not, as tested by the Kolmogorov–Smirnov test. A p value of less than 0.05 was considered significant.
Results
Evaluation of baseline clinical and demographic characteristics, demonstrated that there was no statistically significant difference between the two groups in terms of age, gender distribution, body mass index, or smoking status (Table 1).
Comparison of basic clinical and angiographic features of patients and controls.
NS, not significant; TFC, TIMI frame count; TIMI, Thrombolysis In Myocardial Infarction study group.
The TFC for all epicardial coronary arteries, and the mean TFC, were significantly higher in the CSF group compared with the control group. Mean TFC of all patients with CSF was higher than in the control group (Table 1).
Serum total bilirubin, direct bilirubin, and indirect bilirubin were lower in patients with CSF than controls (14.0 ± 12.0 versus 6.15 ± 6.8, 5.6 ± 3.4 versus 2.6 ± 1.7, and 8.4 ± 8.5 versus 3.6 ± 3.4 µmol/l; all p < 0.001, respectively). Other biochemical variables were not statistically significantly different between the two groups (Table 2). In addition, there were no statistically significant differences between the two groups with regard to leukocyte count, platelet count, hemoglobin, or hematocrit level (Table 2).
Comparison of biochemical and whole blood count features of patients and controls.
NS: not significant.
Discussion
In the present study, we have found that total serum bilirubin levels are significantly lower in CSF patient groups compared with controls. To the best of our knowledge, our study is the first report focusing on the relationship between bilirubin and CSF.
The pathophysiology of CSF has not been clearly identified yet, although multiple abnormalities including inflammation, oxidative stress, endothelial dysfunction, vasculitis, platelet function disorder, and atherothrombosis have been reported [Gökçe et al. 2005; Pekdemir et al. 2004; Yücel et al. 2013].
Previous studies have demonstrated that C-reactive protein (CRP), interleukin-6 levels, and neutrophil lymphocyte ratio (NLR) were higher in patients with CSF than in control participants. The increased levels of CRP and NLR may suggest that these markers could be used in clinical practice for the assessment of the inflammatory status of CSF [Barutçu et al. 2007; Li et al. 2007].
The relationship between low bilirubin levels and increased cardiovascular risk is well known.
Recently, a low serum bilirubin level has been proposed as a useful biomarker for predicting cardiovascular risk. Recent evidence suggests that bilirubin acts as a potent physiologic antioxidant and anti-inflammatory. Recently studies have shown that elevated serum bilirubin concentrations provide important protection against atherosclerotic diseases [Hopkins et al. 1996; Djouse et al. 2001; Mayer, 2000].
Several authors have suggested that bilirubin plays a potential role in inhibition of lipid oxidation [Schwertner, 1998; Stocker et al. 1987].
Previous studies have shown that plasma bilirubin concentration is correlated inversely with several risk factors for CAD such as smoking, diabetes, and obesity, and correlated directly with high-density lipoprotein cholesterol [Schwertner, 1998; Madhavan et al. 1997].
The inverse correlation between the presence of CAD, peripheral arterial disease, carotid intima-media thickness, and bilirubin has been reported in several studies. Subnormal levels of plasma bilirubin are associated with premature CAD and cardiovascular morbidity [Breimer et al. 1994; Ishizaka et al. 2001].
In a previous study, the 3-year incidence of CAD was significantly lower in patients with Gilbert syndrome [Vitek, 2002].
Elevated concentrations of plasma bilirubin were suggested to be able to prevent atherogenesis. A strong ability to scavenge peroxyl radicals and the antioxidant capacity of bilirubin functioning, even in a slightly increased concentration in circulation, have led to the concept that it may have a physiologic function to protect against disease processes involving oxygen and peroxyl radicals [Nakagami et al. 1993; Siow et al. 1999]. In a previous study, Gullu and colleagues showed that elevated concentrations of bilirubin might serve as a protective factor in the development of coronary flow reserve impairment, coronary microvascular dysfunction, and possibly in the development of coronary atherosclerosis. They concluded that bilirubin shows the beneficial effects independent of the known coronary risk factors [Gullu et al. 2005].
Induced hyperbilirubinemia was associated with a significant improvement of endothelial function in type 2 diabetes mellitus [Dekker et al. 2011]. Bilirubin also inhibits vascular cell adhesion molecule 1 and blocks vascular smooth muscular cell proliferation [Ollinger et al. 2005].
As far as we know, there is no study available in the literature regarding the association between CSF and serum bilirubin levels. Our study is important for this reason and we ascertained if there is an association between bilirubin and CSF.
When two groups were compared in our study, serum bilirubin levels of patients with CSF were significantly lower than the levels of the control groups.
In conclusion, it was found in our study that there might be an association between CSF and serum bilirubin. The measurement of bilirubin may also be used to indicate increased risk of CSF-related adverse cardiovascular events. The most important restriction of our study was the limited number of patients and no obstructive CAD group. Another limitation was that angiographic diagnosis of normal coronary arteries was based on axial contrast angiograms of the vessel lumen, which underestimates the presence of atherosclerotic plaques. Further studies are required to determine the relation between bilirubin and CSF.
We have shown for the first time that patients with CSF have lower bilirubin levels compared with controls.
Footnotes
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Conflict of interest statement
The authors declare no conflicts of interest in preparing this article.