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 MRI scans of patients were obtained using a 3 Tesla MRI device (Siemens MAGNETOM ® Verio, Erlangen, Germany) with a gradient power of 45 mT/m. A 6-channel body coil was placed on the front chest wall while the patient was lying in the supine position with ECG pads placed properly. Multiplanar scout images were obtained with the phase-sensitive inversion- recovery (PSIR) turbo FLASH sequence using a repeated breath-hold MRI-technique. Standart long-axis, 2-chamber, 4-chamber and short- axis images of heart were obtained by aligning the mitral valve and the apex. Imaging parameters were: repetition time (TR) = 800ms; echo time (TE) = 6.66ms; slice thickness = 8 mm; matrix = 128x256 and field of view (FOV) = 400 mm. T1, T2 weighted images accompanied by ‘inversion recovery’ pulse for the suppression of blood signals (dark blood) and the turbo spin echo sequence were obtained in order to evaluate the myocardial morphology (TR/TE/ thickness/ matrix/ FOV: 698/6.6/ 8 mm/ 128x256, 360 mm). Dynamic first-pass myocardial perfusion imaging with SR Turbo FLASH (TfI) pulse sequence was acquired after 0.025 mmol/kg Gd-DTPA (Magnevist; Bayer Healthcare, Wayne NJ, USA) was administered intravenously. In eight-minute resting intervals, cine short axis gradient echo sequences for functional imaging of the ventricles were obtained throughout cardiac cycle using the breath-hold technique (TR/TE/ thickness/ matrix/ FOV: 40,24/ TE/ 8 mm/128x256/ 360 mm). Short-axis and 4-chamber images were obtained with T1-weighted PSIR technique, approximately in the 8th minute after the contrast was applied (TR/TE/ thickness/ matrix/ FOV: 756/ TE: 1,15/ 6 mm/ 128x256/360 mm). Total imaging duration lasted 35 minutes on average. The cost of CMR and plasma NT-proBNP testing were covered by the Scientific Research Projects Unit of the Gazi University. Magnetic Resonance Image Analysis All CMR images were transferred to the work station for analysis (Siemens multimodality workplace, Leonardo, Siemens Healthcare). All evaluations were performed visually. CMR studies were retrospectively evaluated by a radiologist experienced for more than 15 years in cardiac imaging, who was blind to the results of echocardiography and coronary angiography examinations. When any perfusion defects or late enhancement were observed during these examinations, they were precisely recorded. Contrast enhancement in perfusion sequences was defined as accomplishing all of the 5 phases after obtaining the highest signal intensity in the left ventricle. CMR results were then compared with the patients’ echocardiography and coronary angiography results. Statistical Analysis The study data were analyzed by using the SPSS (SPSS Inc., Chicago, version 21.0) program. The variables were examined using visual (histograms, probability plots) and analytical methods (the Kolmogorov-Simirnov test) to determine whether or not they were normally distributed. Descriptive analyses were presented with the values and standard deviations for the normally distributed variables, and with the median (interquartile range), for the non-normally distributed variables. Categorical variables were presented using percentages. Independent samples t-test and the Mann-Whitney U test were used to compare the numerical variables. Pearson’s Chi-square analysis was used to compare the categorical data, but Fisher’s exact test was performed when two of the expected values were below 5 or one of the expected value was below 2. A difference with a p-value <0.05 was considered statistically significant. Results A total of 35 patients were included in the study. Patients were divided into 2 groups as the patient group and the control group. Nineteen patients were identified comprising the group with slow flow in LAD, and 16 patients with normal coronary flow were included in the control group (Figure 1). The patients in the control group were matched for their risk factors to the individuals in the patient group. The mean age of the patients was 50.3 ± 10.7, and 6 out of 35 patients (17%) were females. Eleven patients (31%) were diabetic, 9 patients (25%) were hypertensive, 5 patients (14%) were dyslipidemic, 18 patients (51%) were smokers and 8 patients (22%) had a positive family history (Table 1). The main complaint was chest pain in all study patients. ECG of all patients was sinus rhythm. Heart rates were between 64/min - 92/min. The average heart rate was 74/ min. In addition, there was no sign of ischemia, hypertrophy or arrhythmia in the ECG. Left ventricular ejection fraction and other echocardiography findings of the patients were normal. In addition, all patients’ treadmill tests were negative. High sensitivity troponin was measured before and after coronary angiography in all patients. All values were below the threshold and there was no increase in troponin values after angiography. The time interval between the CMR examinations and catheter coronary angiography of the patients was scheduled not to be longer than 21 days. When patients with slow flow were compared with the control group, no significant differences were found in NT- proBNP values (p=0.247). The positive CMR results were significantly more common in the patients with the slow flow (p=0.001) (Table 1). Scar tissue was found at varying levels in the cardiac apex of 7 patients (Figures 2 and 5) and at the inferior and inferolateral regions in 3 patients (Figures 3,4,6,7 and 8). No scar tissues were found in 9 patients (Figure 9). Demographic characteristics and TIMI grade flow were not different in the CMR positive group compared to the MRI negative group (Table 2). NT-proBNP levels were statistically significant in patients with slow flow and scar tissue in CMR (p=0.022) (Table 2). All subjects completed treadmill exercise testing using the Bruce protocol. All patients had exercise capacity over 7 mets. Treadmill tests were terminated on the patients’ own request. There was no significant ST depression (≥1 mm) or T negativity in any exercise test. Metabolic equivalent (MET) values were different in the control, slow flow, and MR positive groups (11.15 ± 1.43; 9.74 ± 2.05; 9.27 ± 2.15, respectively; p=0.027 for the control group vs. the slow flow group; p=0.013 for the group control vs. the MR positive group). There were no differences in MET values between 542