ABC | Volume 114, Nº3, March 2020

Original Article Candemir et al. Slow Flow and Magnetic Resonance Imaging Arq Bras Cardiol. 2020; 114(3):540-551 presence of fibrosis in the myocardial tissue according to the findings of late gadolinium enhancement in CMR. This study aimed at investigating the presence of myocardial fibrosis in patients with slow flow in the left anterior descending coronary artery by using the late gadolinium enhancement technique in CMR. In addition, it aimed at evaluating the relationship between myocardial fibrosis and NT-proBNP levels. Materials and Methods Study Population Among the patients who were admitted to our department between January 2015 - August 2016 and who underwent coronary angiography for chest pain, 19 patients with the coronary slow flow phenomenon in LAD were included in this prospective cohort study. The control group included sixteen patients whose epicardial arteries were entirely normal with a normal coronary flow. This study was approved by the ethics committee of the Gazi University Hospital and was conducted in accordance with the principles of the Helsinki declaration. Exclusion Criteria The following patients were excluded from the study: patients with coronary artery ectasia or atherosclerotic lesions in left main and left anterior descending coronary arteries; patients who underwent percutaneous coronary intervention; patients scheduled to undergo coronary artery intervention; patients with >50% stenosis in any coronary artery; patients with a prior history of MI; patients with <50% left ventricular systolic function; patients with claustrophobia, heart failure or valve dysfunction, ventricular extrasystoles or atrioventricular conduction abnormalities, and branch block or atrial fibrillation; patients with positive treadmill test; patients with restrictive, hypertrophic or dilated cardiomyopathies; patients with known systemic disease (hyperthyroidism, hypothyroidism, malignancy, autoimmune disease, infection or any of the pulmonary, hepatic, renal, hematologic disorders); patients with a history of myocarditis, whose GFRs are <80 ml / min and patients who refused to participate in the study. Patient Data The study patients were measured for height, weight, and body mass index (BMI). Patients’ age, gender, cardiovascular risk factors (hypertension, diabetes, dyslipidemia, smoking and family history), demographic characteristics and comorbid diseases were recorded. Electrocardiography (ECG) was obtained for all patients and all of them demonstrated a sinus rhythm. All study patients were examined on the right lateral decubitus position with a Vivid 7-Pro Ultrasound system (Vingmed Electronic, GE, Horten, Norway), equipped with a 2.5 MHz probe, through simultaneous one-lead ECG recording. M-mode and Doppler measurements were performed in accordance with the recommendations of the American Echocardiography Association. 12 Exercise test was performed at an average of 3 days before angiography in all patients (GE medical system, Milwaukee, USA), according to the standard Bruce protocol test, with standard ECG, blood pressure and heart rate measurements performed at prespecified time points, as per relevant guidelines. 13 Blood samples for the quantification of NT-proBNP were collected through the angiography sheath immediately before its removal. After the collection, they were centrifuged for 10 min at 4500 rpm and stored at -20 ºC until the time when the isolated serum was analyzed. On the day of the analysis, after the samples reached room temperature, an electrochemiluminescence immunoassay was performed with the Roche Cobas e 411 analyzer (Roche Diagnostics GmbH, Mannheim, Germany). The results were presented in picograms per ml (pg/ml). The coefficent of variation value for the NT-proBNP was found below 5% via this method. Coronary Angiography and Timi Frame Count Coronary angiography was performed using the standard Judkins technique with a femoral approach and at 30 frames per second, using Toshiba Infinix cardiac angiography (Toshiba Corporation, Tochigi, Japan). Iopromide (Ultravist-370; Bayer Pharma AG, Berlin, Germany) was used as contrast agent during coronary angiography. An average of 6 to 8 ml of contrast agent was injected manually for each exposure. Coronary arteries were visualized through left and right oblique views with appropiate cranial or caudal angles. The speed of flow at LAD was assessed in right or left anterior oblique views often with caudal angle. The images were evaluated by two clinical specialists who were blind to the clinical findings of the patients. Quantitative evaluation of coronary flow was performed in accordance with the TIMI-4 study, by counting cine frames, starting from the time of contrast agent administration, until it reached to a certain distal point. 14 The methodology of frame count was standardized for each epicardial vessel. TIMI frame counting started with the first frame in which the dye completely filled in the artery. The complete filling of the artery was determined by meeting the following three criteria: (1) A column of almost or fully concentrated dye should extend across the entire width of the origin of the artery; (2) The dye should touch both borders of the origin of the artery; and (3) there should be an antegrade motion of the dye. The last frame counted was the one in which the dye first enterered the end-point branch of the target artery. A complete opacification was not required at the distal segment. LAD and TIMI frame counts were 1.7 times longer than the mean of the RCA and CX counts. Therefore, the longer LAD frame counts were corrected by dividing by 1.7 to derive the corrected TIMI frame count (CTFC). In our study, coronary flow for LAD was accepted to be normal when the TIMI frame count was <23 and it was accepted as slow when the TIMI frame count was ≥ 23. 15,16 Magnetic Resonance Imaging Technique CMR was performed after a median of 8 days (range 0-21 days) after coronary angiography. Standard sequences of cardiac MR perfusion studies were used in all patients. The left antecubital vein was used for intravenous contrast injection. 541