The relation between endothelial dependent flow mediated dilation of the brachial artery and coronary collateral development – a cross sectional study

All patients who underwent coronary angiography at our institution, and were found to have at least one major coronary occlusion, or a stenosis of ≥ 95% with Thrombolysis In Myocardial Infarction (TIMI) grade ≤ 1 anterograde flow were screened for eligibility. Patients with diagnosis of acute coronary syndrome within the past 15 days, and patients who have undergone coronary angiography using right radial approach were excluded. Patients with a history of coronary bypass surgery were also excluded if (1) the operation has been done within the past 30 days, and (2) the distal aspect of the qualifying severely stenosed or occluded artery is supplied by the patent bypass graft.

All patients gave written informed consent and local ethics committee approved the study protocol.

Coronary angiography was routinely performed by the Judkins method without the use of nitroglycerin. Percentage diameter stenosis was measured by using computerized quantitative angiography in a biplane mode (Philips DCI, Eindhoven, Netherlands). Two experienced interventional cardiologists (A.O.O and C.T.K) who were blinded to patient characteristics reviewed the angiograms and graded the coronary collaterals according to Rentrop classification [14]. In subjects with >1 collateral supplying the distal aspect of the diseased artery, the higher collateral grade was used. In subjects with >1 qualifying severely diseased vessel, the vessel with the higher collateral grade was chosen for analysis.

Information about smoking, and alcohol consumption was collected through interview directly from the patients. Medical records were reviewed for reports of previous myocardial infarction, coronary artery bypass grafting, and percutaneous coronary intervention. Body mass index was calculated as weight (kg) divided by height (m²). Hypertension was defined as systolic blood pressure ≥ 140 mm Hg, diastolic blood pressure ≥ 90 mm Hg, or use of antihypertensive medication in the previous two weeks. Diabetes was defined as fasting blood glucose ≥ 126 mg/dL, nonfasting blood glucose ≥ 200 mg/dL, or use of antidiabetic medication in the previous two weeks. Diagnosis of acute coronary syndrome (ACS) was made according to the guidelines established by the American College of Cardiology and the American Heart Association [15]. Non-ACS patients had stable angina and/or positive stress tests.

Left ventricular ejection fraction was calculated by contrast venticulography using a standard area-length formula [16] (n = 65) or estimated by echocardiography when ventriculography was not performed (n = 106). Significant stenosis was defined as quantitatively measured diameter stenosis of >70% in any of the major coronary arteries.

Endothelium dependent and independent flow-mediated dilation were performed by using a 13.0 MHz linear array transducer (Vivid 7, Wipro GE Healtcare, GE Medical Systems Inc, Chicago, U.S.A) on the day after coronary angiography. After 12 h fasting (including caffeine, nicotine and alcohol), vascular measurements were performed in a quiet, temperature controlled (22–24°C) room early in the morning (8 am-10 am). Vasoactive medications were not stopped before FMD, but the morning doses were skipped on the examination day of FMD. After 15 min resting period in the supine position, the transducer was placed 4–5 cm above the elbow in the longitudinal section for the scanning of right brachial artery, then the basal diameter of brachial artery (from anterior intima to posterior intima) and flow velocity were measured. Afterwards, sphygmomamometer cuff was placed on the upper arm, and inflated at 250 mmHg for 4–5 min, and deflated abruptly. The flow velocity was recorded within 15 seconds, and postocclusion artery diameters were taken at 60–120 seconds. After a 10 minutes resting interval, 5 mg sublingual isosorbide dinitrate was administered, and brachial artery was scanned within the next 5 minutes. Brachial artery images were taken by two experienced observers (N.U and S.T) who were blinded to the collateral status of the patients. Diameter measurements were taken at the end of the diastole (timed by peak of R wave on electrocardiogram), which were calculated at least three times, and the average of these measurements were determined. Endothelium dependent and independent vasodilations were defined as the percent change in diameter compared with baseline (maximum diameter-baseline diameter/baseline diameterx100). Two sample cases of impaired, and preserved endothelium dependent FMD measurements have been demonstrated in Figures 1 and 2. Intra- and inter-observer variability of FMD measurements were determined from 40 randomly selected brachial artery images (Kappa values were 0.93 for intra- and 0.82 for inter-observer agreements; p < 0.001 for both of them).

Data are expressed as mean ± standard deviation for continuous variables, and number and percentage of subjects for categorical ones. Chi-square test with Yates correction was used to assess the significance of difference between categorical variables. When the values in the cells were not enough for chi-square test, Fischer's exact test was used. Continuous variables were compared by Student t-test or the Mann-Whitney rank sum test. Multivariable logistic regression analysis was used to adjust for the characteristics that were significant correlates of collateral development in the univariate analysis (with p < 0.1) plus terms for age and gender due to their well-established association with coronary heart disease. Odds ratios (OR) with two-tailed p-values and 95% confidence intervals (CI) were calculated as a measure of the association of the clinical, and therapy-related characteristics with collateral development. Statistical analyses were performed using SPSS software package (SPSS Inc., Chicago, Illinois, USA) version 16.0 for Windows and p < 0.05 was considered statistically significant.